Nicholas J Strausfeld

Interests

Teaching

Teaching courses in neurobiology, emphasizing the value of cross-taxonomic comparisons, the avoidance of narrow-minded "model-systems" research, and the crucial integration of evolutionary considerations with respect to every facet of the neurosciences.

Research

Brain organization in invertebrates - brain evolution - identification of arthropod-vertebrate brain homologies - neuropalaeontology - vision research - animal behavior.

Courses

Scholarly Contributions

Books

• Strausfeld, N. (2012). Arthropod Brains. Evolution, Functional Elegance, and Historical Significance. Harvard University Press.

Chapters

• Strausfeld, N. J. (2017). The Insect Visual System: Correspondence with Vertebrates and with Olfactory Processing. In Handbook of Brain Microscircuits (Eds. G.M. Shpherd, S. Grillner) pp. 293-308.. doi:10.1093/med/9780190636111.003.0024
• Wolff, G. H., & Strausfeld, N. J. (2015). The Insect Brain: A COMMENTATED PRIMER. In In: Structure and Evolution of Invertebrate Nervous Systems, 1st ed.; Schmidt-Rhaesa, A., Harzsch, S., Purschke, G., Eds.; Oxford University Press: Oxford, UK, 2016; pp. .(pp 597–639). Oxford University Press. doi:10.1093/ACPROF:OSO/9780199682201.003.0047
• Strausfeld, N. J., & Wolff, G. H. (2016). The Insect Brain: A Commentated Primer. In Structure and Evolution of Invertebrate Nervous Systems(pp 597-639). Oxford: Oxford University Press.

Journals/Publications

• Strausfeld, N. J., Hou, X., Sayre, M. E., & Hirth, F. (2022). The lower Cambrian lobopodian Cardiodictyon resolves the origin of euarthropod brains. Science, 378(6622), 905-909. doi:10.1126/science.abn6264
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  For more than a century, the origin and evolution of the arthropod head and brain have eluded a unifying rationale reconciling divergent morphologies and phylogenetic relationships. Here, clarification is provided by the fossilized nervous system of the lower Cambrian lobopodian Cardiodictyon catenulum , which reveals an unsegmented head and brain comprising three cephalic domains, distinct from the metameric ventral nervous system serving its appendicular trunk. Each domain aligns with one of three components of the foregut and with a pair of head appendages. Morphological correspondences with stem group arthropods and alignments of homologous gene expression patterns with those of extant panarthropods demonstrate that cephalic domains of C. catenulum predate the evolution of the euarthropod head yet correspond to neuromeres defining brains of living chelicerates and mandibulates.
• Strausfeld, N. J., Steinbrenner, A. D., Snell, E. H., Royer, C. A., Murphy, C. A., Morris, J. T., Kim, H., Jolles, A. E., Caetano-anolles, G., & Bogdan, P. (2022). Biological Networks across Scales-The Theoretical and Empirical Foundations for Time-Varying Complex Networks that Connect Structure and Function across Levels of Biological Organization.. Integrative and comparative biology, 61(6), 1991-2010. doi:10.1093/icb/icab069
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  Many biological systems across scales of size and complexity exhibit a time-varying complex network structure that emerges and self-organizes as a result of interactions with the environment. Network interactions optimize some intrinsic cost functions that are unknown and involve for example energy efficiency, robustness, resilience, and frailty. A wide range of networks exist in biology, from gene regulatory networks important for organismal development, protein interaction networks that govern physiology and metabolism, and neural networks that store and convey information to networks of microbes that form microbiomes within hosts, animal contact networks that underlie social systems, and networks of populations on the landscape connected by migration. Increasing availability of extensive (big) data is amplifying our ability to quantify biological networks. Similarly, theoretical methods that describe network structure and dynamics are being developed. Beyond static networks representing snapshots of biological systems, collections of longitudinal data series can help either at defining and characterizing network dynamics over time or analyzing the dynamics constrained to networked architectures. Moreover, due to interactions with the environment and other biological systems, a biological network may not be fully observable. Also, subnetworks may emerge and disappear as a result of the need for the biological system to cope with for example invaders or new information flows. The confluence of these developments renders tractable the question of how the structure of biological networks predicts and controls network dynamics. In particular, there may be structural features that result in homeostatic networks with specific higher-order statistics (e.g., multifractal spectrum), which maintain stability over time through robustness and/or resilience to perturbation. Alternative, plastic networks may respond to perturbation by (adaptive to catastrophic) shifts in structure. Here, we explore the opportunity for discovering universal laws connecting the structure of biological networks with their function, positioning them on the spectrum of time-evolving network structure, that is, dynamics of networks, from highly stable to exquisitely sensitive to perturbation. If such general laws exist, they could transform our ability to predict the response of biological systems to perturbations-an increasingly urgent priority in the face of anthropogenic changes to the environment that affect life across the gamut of organizational scales.
• Strausfeld, N. J., & Strausfeld, N. J. (2021). Mushroom bodies and reniform bodies coexisting in crabs cannot both be homologs of the insect mushroom body.. The Journal of comparative neurology, 529(12), 3265-3271. doi:10.1002/cne.25152
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  In one species of shore crab (Brachyura, Varunidae), a center that supports long-term visual habituation and that matches the reniform body's morphology has been claimed as a homolog of the insect mushroom body despite lacking traits that define it as such. The discovery in a related species of shore crab of a mushroom body possessing those defining traits renders that interpretation unsound. Two phenotypically distinct, coexisting centers cannot both be homologs of the insect mushroom body. The present commentary outlines the history of research leading to misidentification of the reniform body as a mushroom body. One conclusion is that if both centers support learning and memory, this would be viewed as a novel and fascinating attribute of the pancrustacean brain.
• Strausfeld, N. J., & Strausfeld, N. J. (2021). The lobula plate is exclusive to insects.. Arthropod structure & development, 61, 101031. doi:10.1016/j.asd.2021.101031
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  Just one superorder of insects is known to possess a neuronal network that mediates extremely rapid reactions in flight in response to changes in optic flow. Research on the identity and functional organization of this network has over the course of almost half a century focused exclusively on the order Diptera, a member of the approximately 300-million-year-old clade Holometabola defined by its mode of development. However, it has been broadly claimed that the pivotal neuropil containing the network, the lobula plate, originated in the Cambrian before the divergence of Hexapoda and Crustacea from a mandibulate ancestor. This essay defines the traits that designate the lobula plate and argues against a homologue in Crustacea. It proposes that the origin of the lobula plate is relatively recent and may relate to the origin of flight.
• Strausfeld, N. J., Steinbrenner, A. D., Snell, E. H., Royer, C. A., Murphy, C. A., Morris, J. T., Kim, H., Jolles, A. E., Caetano-anolles, G., & Bogdan, P. (2021). Biological networks across scales.. Integrative and comparative biology. doi:10.1093/icb/icab069
  More info

  Many biological systems across scales of size and complexity exhibit a time-varying complex network structure that emerges and self-organizes as a result of interactions with the environment. Network interactions optimize some intrinsic cost functions that are unknown and involve for example energy efficiency, robustness, resilience, and frailty. A wide range of networks exist in biology, from gene regulatory networks important for organismal development, protein interaction networks that govern physiology and metabolism, and neural networks that store and convey information to networks of microbes that form microbiomes within hosts, animal contact networks that underlie social systems, and networks of populations on the landscape connected by migration. Increasing availability of extensive (big) data is amplifying our ability to quantify biological networks. Similarly, theoretical methods that describe network structure and dynamics are being developed. Beyond static networks representing snapshots of biological systems, collections of longitudinal data series can help either at defining and characterizing network dynamics over time or analyzing the dynamics constrained to networked architectures. Moreover, due to interactions with the environment and other biological systems, a biological network may not be fully observable. Also, subnetworks may emerge and disappear as a result of the need for the biological system to cope with for example invaders or new information flows. The confluence of these developments renders tractable the question of how the structure of biological networks predicts and controls network dynamics. In particular, there may be structural features that result in homeostatic networks with specific higher-order statistics (e.g., multifractal spectrum), which maintain stability over time through robustness and/or resilience to perturbation. Alternative, plastic networks may respond to perturbation by (adaptive to catastrophic) shifts in structure. Here, we explore the opportunity for discovering universal laws connecting the structure of biological networks with their function, positioning them on the spectrum of time-evolving network structure, i.e. dynamics of networks, from highly stable to exquisitely sensitive to perturbation. If such general laws exist, they could transform our ability to predict the response of biological systems to perturbations-an increasingly urgent priority in the face of anthropogenic changes to the environment that affect life across the gamut of organizational scales.
• Strausfeld, N. J., Strausfeld, N. J., Olea-rowe, B., & Olea-rowe, B. (2021). Convergent evolution of optic lobe neuropil in Pancrustacea.. Arthropod structure & development, 61, 101040. doi:10.1016/j.asd.2021.101040
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  A prevailing opinion since 1926 has been that optic lobe organization in malacostracan crustaceans and insects reflects a corresponding organization in their common ancestor. Support for this refers to malacostracans and insects both possessing three, in some instances four, nested retinotopic neuropils beneath their compound eyes. Historically, the rationale for claiming homology of malacostracan and insect optic lobes referred to those commonalities, and to comparable arrangements of neurons. However, recent molecular phylogenetics has firmly established that Malacostraca belong to Multicrustacea, whereas Hexapoda and its related taxa Cephalocarida, Branchiopoda, and Remipedia belong to the phyletically distinct clade Allotriocarida. Insects are more closely related to remipedes than are either to malacostracans. Reconciling neuroanatomy with molecular phylogenies has been complicated by studies showing that the midbrains of remipedes share many attributes with the midbrains of malacostracans. Here we review the organization of the optic lobes in Malacostraca and Insecta to inquire which of their characters correspond genealogically across Pancrustacea and which characters do not. We demonstrate that neuroanatomical characters pertaining to the third optic lobe neuropil, called the lobula complex, may indicate convergent evolution. Distinctions of the malacostracan and insect lobula complexes are sufficient to align neuroanatomical descriptions of the pancrustacean optic lobes within the constraints of molecular-based phylogenies.
• Strausfeld, N. J., Strausfeld, N. J., Sayre, M. E., & Sayre, M. E. (2021). Shore crabs reveal novel evolutionary attributes of the mushroom body.. eLife, 10, 1-38. doi:10.7554/elife.65167
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  Neural organization of mushroom bodies is largely consistent across insects, whereas the ancestral ground pattern diverges broadly across crustacean lineages resulting in successive loss of columns and the acquisition of domed centers retaining ancestral Hebbian-like networks and aminergic connections. We demonstrate here a major departure from this evolutionary trend in Brachyura, the most recent malacostracan lineage. In the shore crab Hemigrapsus nudus, instead of occupying the rostral surface of the lateral protocerebrum, mushroom body calyces are buried deep within it with their columns extending outwards to an expansive system of gyri on the brain's surface. The organization amongst mushroom body neurons reaches extreme elaboration throughout its constituent neuropils. The calyces, columns, and especially the gyri show DC0 immunoreactivity, an indicator of extensive circuits involved in learning and memory.
• Zhao, Y., Zhao, F., Strausfeld, N. J., Martinez, P., Lan, T., & He, Y. (2021). Leanchoiliidae reveals the ancestral organization of the stem euarthropod brain.. Current biology : CB, 31(19), 4397-4404.e2. doi:10.1016/j.cub.2021.07.048
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  Fossils provide insights into how organs may have diversified over geological time.1 However, diversification already accomplished early in evolution can obscure ancestral events leading to it. For example, already by the mid-Cambrian period, euarthropods had condensed brains typifying modern mandibulate lineages.2 However, the demonstration that extant euarthropods and chordates share orthologous developmental control genes defining the segmental fore-, mid-, and hindbrain suggests that those character states were present even before the onset of the Cambrian.3 Fossilized nervous systems of stem Euarthropoda might, therefore, be expected to reveal ancestral segmental organization, from which divergent arrangements emerged. Here, we demonstrate unsurpassed preservation of cerebral tissue in Kaili leanchoiliids revealing near-identical arrangements of bilaterally symmetric ganglia identified as the proto-, deuto-, and tritocerebra disposed behind an asegmental frontal domain, the prosocerebrum, from which paired nerves extend to labral ganglia flanking the stomodeum. This organization corresponds to labral connections hallmarking extant euarthropod clades4 and to predicted transformations of presegmental ganglia serving raptorial preocular appendages of Radiodonta.5 Trace nervous system in the gilled lobopodian Kerygmachela kierkegaardi6 suggests an even deeper prosocerebral ancestry. An asegmental prosocerebrum resolves its location relative to the midline asegmental sclerite of the radiodontan head, which persists in stem Euarthropoda.7 Here, data from two Kaili Leanchoilia, with additional reference to Alalcomenaeus,8,9 demonstrate that Cambrian stem Euarthropoda confirm genomic and developmental studies10-15 claiming that the most frontal domain of the euarthropod brain is a unique evolutionary module distinct from, and ancestral to, the fore-, mid-, and hindbrain.
• Zhao, Y., Zhao, F., Strausfeld, N. J., Martinez, P., Lan, T., & He, Y. (2021). Leanchoiliidae reveals the ancestral organization of the stem euarthropod brain.. Current biology : CB. doi:10.1016/j.cub.2021.07.048
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  Fossils provide insights into how organs may have diversified over geological time.1 However, diversification already accomplished early in evolution can obscure ancestral events leading to it. For example, already by the mid-Cambrian period, euarthropods had condensed brains typifying modern mandibulate lineages.2 However, the demonstration that extant euarthropods and chordates share orthologous developmental control genes defining the segmental fore-, mid-, and hindbrain suggests that those character states were present even before the onset of the Cambrian.3 Fossilized nervous systems of stem Euarthropoda might, therefore, be expected to reveal ancestral segmental organization, from which divergent arrangements emerged. Here, we demonstrate unsurpassed preservation of cerebral tissue in Kaili leanchoiliids revealing near-identical arrangements of bilaterally symmetric ganglia identified as the proto-, deuto-, and tritocerebra disposed behind an asegmental frontal domain, the prosocerebrum, from which paired nerves extend to labral ganglia flanking the stomodeum. This organization corresponds to labral connections hallmarking extant euarthropod clades4 and to predicted transformations of presegmental ganglia serving raptorial preocular appendages of Radiodonta.5 Trace nervous system in the gilled lobopodian Kerygmachela kierkegaardi6 suggests an even deeper prosocerebral ancestry. An asegmental prosocerebrum resolves its location relative to the midline asegmental sclerite of the radiodontan head, which persists in stem Euarthropoda.7 Here, data from two Kaili Leanchoilia, with additional reference to Alalcomenaeus,8,9 demonstrate that Cambrian stem Euarthropoda confirm genomic and developmental studies10-15 claiming that the most frontal domain of the euarthropod brain is a unique evolutionary module distinct from, and ancestral to, the fore-, mid-, and hindbrain.
• Li, G., Forero, M. G., Wentzell, J. S., Durmus, I., Wolf, R., Anthoney, N. C., Parker, M., Jiang, R., Hasenauer, J., Strausfeld, N. J., Heisenberg, M., & Hidalgo, A. (2020). A Toll-receptor map underlies structural brain plasticity.. eLife, 9, 1-32. doi:10.7554/elife.52743
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  Experience alters brain structure, but the underlying mechanism remained unknown. Structural plasticity reveals that brain function is encoded in generative changes to cells that compete with destructive processes driving neurodegeneration. At an adult critical period, experience increases fiber number and brain size in Drosophila. Here, we asked if Toll receptors are involved. Tolls demarcate a map of brain anatomical domains. Focusing on Toll-2, loss of function caused apoptosis, neurite atrophy and impaired behaviour. Toll-2 gain of function and neuronal activity at the critical period increased cell number. Toll-2 induced cycling of adult progenitor cells via a novel pathway, that antagonized MyD88-dependent quiescence, and engaged Weckle and Yorkie downstream. Constant knock-down of multiple Tolls synergistically reduced brain size. Conditional over-expression of Toll-2 and wek at the adult critical period increased brain size. Through their topographic distribution, Toll receptors regulate neuronal number and brain size, modulating structural plasticity in the adult brain.
• Strausfeld, N. J. (2020). Nomen est omen, cognitive dissonance, and homology of memory centers in crustaceans and insects.. The Journal of comparative neurology, 528(15), 2595-2601. doi:10.1002/cne.24919
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  In 1882, the Italian embryologist Giuseppe Bellonci introduced a nomenclature for structures in the stomatopod crustacean Squilla mantis that he claimed correspond to insect mushroom bodies, today recognized as cardinal centers that in insects mediate associative memory. The use of Bellonci's terminology has, through a series of misunderstandings and entrenched opinions, led to contesting views regarding whether centers in crustacean and insect brains that occupy corresponding locations and receive comparable multisensory inputs are homologous or homoplasic. The following describes the fate of terms used to denote sensory association neuropils in crustacean species and relates how those terms were deployed in the 1920s and 1930s by the Swedish neuroanatomist Bertil Hanström to claim homology in insects and crustaceans. Yet the same terminology has been repurposed by subsequent researchers to promote the very opposite view: that mushroom bodies are a derived trait of hexapods and that equivalent centers in crustaceans evolved independently.
• Strausfeld, N. J., & Sayre, M. E. (2020). Mushroom bodies in Reptantia reflect a major transition in crustacean brain evolution.. The Journal of comparative neurology, 528(2), 261-282. doi:10.1002/cne.24752
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  Brain centers possessing a suite of neuroanatomical characters that define mushroom bodies of dicondylic insects have been identified in mantis shrimps, which are basal malacostracan crustaceans. Recent studies of the caridean shrimp Lebbeus groenlandicus further demonstrate the existence of mushroom bodies in Malacostraca. Nevertheless, received opinion promulgates the hypothesis that domed centers called hemiellipsoid bodies typifying reptantian crustaceans, such as lobsters and crayfish, represent the malacostracan cerebral ground pattern. Here, we provide evidence from the marine hermit crab Pagurus hirsutiusculus that refutes this view. P. hirsutiusculus, which is a member of the infraorder Anomura, reveals a chimeric morphology that incorporates features of a domed hemiellipsoid body and a columnar mushroom body. These attributes indicate that a mushroom body morphology is the ancestral ground pattern, from which the domed hemiellipsoid body derives and that the "standard" reptantian hemiellipsoid bodies that typify Astacidea and Achelata are extreme examples of divergence from this ground pattern. This interpretation is underpinned by comparing the lateral protocerebrum of Pagurus with that of the crayfish Procambarus clarkii and Orconectes immunis, members of the reptantian infraorder Astacidea.
• Strausfeld, N. J., Strausfeld, N. J., Ludlow, Z. N., Ludlow, Z. N., Kottler, B., Kottler, B., Hirth, F., Hirth, F., Hartmann, B., Hartmann, B., Goker, M., Goker, M., Dearlove, J., Dearlove, J., Callaerts, P., Callaerts, P., Broeck, L. V., Broeck, L. V., Bridi, J. C., & Bridi, J. C. (2020). Ancestral regulatory mechanisms specify conserved midbrain circuitry in arthropods and vertebrates.. Proceedings of the National Academy of Sciences of the United States of America, 117(32), 19544-19555. doi:10.1073/pnas.1918797117
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  Corresponding attributes of neural development and function suggest arthropod and vertebrate brains may have an evolutionarily conserved organization. However, the underlying mechanisms have remained elusive. Here, we identify a gene regulatory and character identity network defining the deutocerebral-tritocerebral boundary (DTB) in Drosophila This network comprises genes homologous to those directing midbrain-hindbrain boundary (MHB) formation in vertebrates and their closest chordate relatives. Genetic tracing reveals that the embryonic DTB gives rise to adult midbrain circuits that in flies control auditory and vestibular information processing and motor coordination, as do MHB-derived circuits in vertebrates. DTB-specific gene expression and function are directed by cis-regulatory elements of developmental control genes that include homologs of mammalian Zinc finger of the cerebellum and Purkinje cell protein 4 Drosophila DTB-specific cis-regulatory elements correspond to regulatory sequences of human ENGRAILED-2, PAX-2, and DACHSHUND-1 that direct MHB-specific expression in the embryonic mouse brain. We show that cis-regulatory elements and the gene networks they regulate direct the formation and function of midbrain circuits for balance and motor coordination in insects and mammals. Regulatory mechanisms mediating the genetic specification of cephalic neural circuits in arthropods correspond to those in chordates, thereby implying their origin before the divergence of deuterostomes and ecdysozoans.
• Strausfeld, N. J., Wolff, G. H., & Sayre, M. E. (2020). Mushroom body evolution demonstrates homology and divergence across Pancrustacea.. eLife, 9. doi:10.7554/elife.52411
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  Descriptions of crustacean brains have focused mainly on three highly derived lineages of malacostracans: the reptantian infraorders represented by spiny lobsters, lobsters, and crayfish. Those descriptions advocate the view that dome- or cap-like neuropils, referred to as 'hemiellipsoid bodies,' are the ground pattern organization of centers that are comparable to insect mushroom bodies in processing olfactory information. Here we challenge the doctrine that hemiellipsoid bodies are a derived trait of crustaceans, whereas mushroom bodies are a derived trait of hexapods. We demonstrate that mushroom bodies typify lineages that arose before Reptantia and exist in Reptantia thereby indicating that the mushroom body, not the hemiellipsoid body, provides the ground pattern for both crustaceans and hexapods. We show that evolved variations of the mushroom body ground pattern are, in some lineages, defined by extreme diminution or loss and, in others, by the incorporation of mushroom body circuits into lobeless centers. Such transformations are ascribed to modifications of the columnar organization of mushroom body lobes that, as shown in Drosophila and other hexapods, contain networks essential for learning and memory.
• Thoen, H. H., Wolff, G. H., Marshall, J., Sayre, M. E., & Strausfeld, N. J. (2020). The reniform body: An integrative lateral protocerebral neuropil complex of Eumalacostraca identified in Stomatopoda and Brachyura.. The Journal of comparative neurology, 528(7), 1079-1094. doi:10.1002/cne.24788
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  Mantis shrimps (Stomatopoda) possess in common with other crustaceans, and with Hexapoda, specific neuroanatomical attributes of the protocerebrum, the most anterior part of the arthropod brain. These attributes include assemblages of interconnected centers called the central body complex and in the lateral protocerebra, situated in the eyestalks, paired mushroom bodies. The phenotypic homologues of these centers across Panarthropoda support the view that ancestral integrative circuits crucial to action selection and memory have persisted since the early Cambrian or late Ediacaran. However, the discovery of another prominent integrative neuropil in the stomatopod lateral protocerebrum raises the question whether it is unique to Stomatopoda or at least most developed in this lineage, which may have originated in the upper Ordovician or early Devonian. Here, we describe the neuroanatomical structure of this center, called the reniform body. Using confocal microscopy and classical silver staining, we demonstrate that the reniform body receives inputs from multiple sources, including the optic lobe's lobula. Although the mushroom body also receives projections from the lobula, it is entirely distinct from the reniform body, albeit connected to it by discrete tracts. We discuss the implications of their coexistence in Stomatopoda, the occurrence of the reniform body in another eumalacostracan lineage and what this may mean for our understanding of brain functionality in Pancrustacea.
• Sayre, M. E., & Strausfeld, N. J. (2019). Mushroom bodies in crustaceans: Insect-like organization in the caridid shrimp Lebbeus groenlandicus.. The Journal of comparative neurology, 527(14), 2371-2387. doi:10.1002/cne.24678
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  Paired centers in the forebrain of insects, called the mushroom bodies, have become the most investigated brain region of any invertebrate due to novel genetic strategies that relate unique morphological attributes of these centers to their functional roles in learning and memory. Mushroom bodies possessing all the morphological attributes of those in dicondylic insects have been identified in mantis shrimps, basal hoplocarid crustaceans that are sister to Eumalacostraca, the most species-rich group of Crustacea. However, unless other examples of mushroom bodies can be identified in Eumalacostraca, the possibility is that mushroom body-like centers may have undergone convergent evolution in Hoplocarida and are unique to this crustacean lineage. Here, we provide evidence that speaks against convergent evolution, describing in detail the paired mushroom bodies in the lateral protocerebrum of a decapod crustacean, Lebbeus groenlandicus, a species belonging to the infraorder Caridea, an ancient lineage of Eumalacostraca.
• Lessios, N., Rutowski, R. L., Cohen, J. H., Sayre, M. E., & Strausfeld, N. J. (2018). Multiple spectral channels in branchiopods. I. Vision in dim light and neural correlates.. The Journal of experimental biology, 221(Pt 10). doi:10.1242/jeb.165860
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  Animals that have true color vision possess several spectral classes of photoreceptors. Pancrustaceans (Hexapoda+Crustacea) that integrate spectral information about their reconstructed visual world do so from photoreceptor terminals supplying their second optic neuropils, with subsequent participation of the third (lobula) and deeper centers (optic foci). Here, we describe experiments and correlative neural arrangements underlying convergent visual pathways in two species of branchiopod crustaceans that have to cope with a broad range of spectral ambience and illuminance in ephemeral pools, yet possess just two optic neuropils, the lamina and the optic tectum. Electroretinographic recordings and multimodel inference based on modeled spectral absorptance were used to identify the most likely number of spectral photoreceptor classes in their compound eyes. Recordings from the retina provide support for four color channels. Neuroanatomical observations resolve arrangements in their laminas that suggest signal summation at low light intensities, incorporating chromatic channels. Neuroanatomical observations demonstrate that spatial summation in the lamina of the two species are mediated by quite different mechanisms, both of which allow signals from several ommatidia to be pooled at single lamina monopolar cells. We propose that such summation provides sufficient signal for vision at intensities equivalent to those experienced by insects in terrestrial habitats under dim starlight. Our findings suggest that despite the absence of optic lobe neuropils necessary for spectral discrimination utilized by true color vision, four spectral photoreceptor classes have been maintained in Branchiopoda for vision at very low light intensities at variable ambient wavelengths that typify conditions in ephemeral freshwater habitats.
• Thoen, H. H., Sayre, M. E., Marshall, J., & Strausfeld, N. J. (2018). Representation of the stomatopod's retinal midband in the optic lobes: Putative neural substrates for integrating chromatic, achromatic and polarization information.. The Journal of comparative neurology, 526(7), 1148-1165. doi:10.1002/cne.24398
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  Stomatopods have an elaborate visual system served by a retina that is unique to this class of pancrustaceans. Its upper and lower eye hemispheres encode luminance and linear polarization while an equatorial band of photoreceptors termed the midband detects color, circularly polarized light and linear polarization in the ultraviolet. In common with many malacostracan crustaceans, stomatopods have stalked eyes, but they can move these independently within three degrees of rotational freedom. Both eyes separately use saccadic and scanning movements but they can also move in a coordinated fashion to track selected targets or maintain a forward eyestalk posture during swimming. Visual information is initially processed in the first two optic neuropils, the lamina and the medulla, where the eye's midband is represented by enlarged regions within each neuropil that contain populations of neurons, the axons of which are segregated from the neuropil regions subtending the hemispheres. Neuronal channels representing the midband extend from the medulla to the lobula where populations of putative inhibitory glutamic acid decarboxylase-positive neurons and tyrosine hydroxylase-positive neurons intrinsic to the lobula have specific associations with the midband. Here we investigate the organization of the midband representation in the medulla and the lobula in the context of their overall architecture. We discuss the implications of observed arrangements, in which midband inputs to the lobula send out collaterals that extend across the retinotopic mosaic pertaining to the hemispheres. This organization suggests an integrative design that diverges from the eumalacostracan ground pattern and, for the stomatopod, enables color and polarization information to be integrated with luminance information that presumably encodes shape and motion.
• Steinbrecht, A., & Strausfeld, N. (2017). Editorial. Arthropod structure & development, 46(1), 1.
• Strausfeld, N. J., Wolff, G. H., Marshall, N. J., & Thoen, H. H. (2017). Insect-Like Organization of the Stomatopod Central Complex: Functional and Phylogenetic Implications. Frontiers in Behavioral Neuroscience. doi:10.3389/fnbeh.2017.00012
• Thoen, H. H., Marshall, J., Wolff, G. H., & Strausfeld, N. J. (2017). Insect-Like Organization of the Stomatopod Central Complex: Functional and Phylogenetic Implications. Frontiers in behavioral neuroscience, 11, 12.
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  One approach to investigating functional attributes of the central complex is to relate its various elaborations to pancrustacean phylogeny, to taxon-specific behavioral repertoires and ecological settings. Here we review morphological similarities between the central complex of stomatopod crustaceans and the central complex of dicondylic insects. We discuss whether their central complexes possess comparable functional properties, despite the phyletic distance separating these taxa, with mantis shrimp (Stomatopoda) belonging to the basal branch of Eumalacostraca. Stomatopods possess the most elaborate visual receptor system in nature and display a fascinating behavioral repertoire, including refined appendicular dexterity such as independently moving eyestalks. They are also unparalleled in their ability to maneuver during both swimming and substrate locomotion. Like other pancrustaceans, stomatopods possess a set of midline neuropils, called the central complex, which in dicondylic insects have been shown to mediate the selection of motor actions for a range of behaviors. As in dicondylic insects, the stomatopod central complex comprises a modular protocerebral bridge (PB) supplying decussating axons to a scalloped fan-shaped body (FB) and its accompanying ellipsoid body (EB), which is linked to a set of paired noduli and other recognized satellite regions. We consider the functional implications of these attributes in the context of stomatopod behaviors, particularly of their eyestalks that can move independently or conjointly depending on the visual scene.
• Thoen, H. H., Strausfeld, N. J., & Marshall, J. (2017). Neural organization of afferent pathways from the stomatopod compound eye.. The Journal of comparative neurology, 525(14), 3010-3030. doi:10.1002/cne.24256
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  Crustaceans and insects share many similarities of brain organization suggesting that their common ancestor possessed some components of those shared features. Stomatopods (mantis shrimps) are basal eumalacostracan crustaceans famous for their elaborate visual system, the most complex of which possesses 12 types of color photoreceptors and the ability to detect both linearly and circularly polarized light. Here, using a palette of histological methods we describe neurons and their neuropils most immediately associated with the stomatopod retina. We first provide a general overview of the major neuropil structures in the eyestalks lateral protocerebrum, with respect to the optical pathways originating from the six rows of specialized ommatidia in the stomatopod's eye, termed the midband. We then focus on the structure and neuronal types of the lamina, the first optic neuropil in the stomatopod visual system. Using Golgi impregnations to resolve single neurons we identify cells in different parts of the lamina corresponding to the three different regions of the stomatopod eye (midband and the upper and lower eye halves). While the optic cartridges relating to the spectral and polarization sensitive midband ommatidia show some specializations not found in the lamina serving the upper and lower eye halves, the general morphology of the midband lamina reflects cell types elsewhere in the lamina and cell types described for other species of Eumalacostraca.
• Thoen, H. H., Strausfeld, N. J., & Marshall, J. (2017). Pathways underlying colour and polarisation processing in stomatopods. Integrative and Comparative Biology, 57.
• Wolff, G. H., Thoen, H. H., Marshall, J., Sayre, M. E., & Strausfeld, N. J. (2017). An insect-like mushroom body in a crustacean brain.. eLife, 6. doi:10.7554/elife.29889
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  Mushroom bodies are the iconic learning and memory centers of insects. No previously described crustacean possesses a mushroom body as defined by strict morphological criteria although crustacean centers called hemiellipsoid bodies, which serve functions in sensory integration, have been viewed as evolutionarily convergent with mushroom bodies. Here, using key identifiers to characterize neural arrangements, we demonstrate insect-like mushroom bodies in stomatopod crustaceans (mantis shrimps). More than any other crustacean taxon, mantis shrimps display sophisticated behaviors relating to predation, spatial memory, and visual recognition comparable to those of insects. However, neuroanatomy-based cladistics suggesting close phylogenetic proximity of insects and stomatopod crustaceans conflicts with genomic evidence showing hexapods closely related to simple crustaceans called remipedes. We discuss whether corresponding anatomical phenotypes described here reflect the cerebral morphology of a common ancestor of Pancrustacea or an extraordinary example of convergent evolution.
• Strausfeld, N. J. (2016). Waptia revisited: Intimations of behaviors. Arthropod Structure & Development. doi:10.1016/j.asd.2015.09.001
• Strausfeld, N. J., & Hirth, F. (2016). Introduction to ‘Homology and convergence in nervous system evolution’. Philosophical Transactions of the Royal Society B, 371(1685), 20150034. doi:10.1098/rstb.2015.0034
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  The origin of brains and central nervous systems (CNSs) is thought to have occurred before the Palaeozoic era 540 Ma. Yet in the absence of tangible evidence, there has been continued debate whether today's brains and nervous systems derive from one ancestral origin or whether similarities among them are due to convergent evolution. With the advent of molecular developmental genetics and genomics, it has become clear that homology is a concept that applies not only to morphologies, but also to genes, developmental processes, as well as to behaviours. Comparative studies in phyla ranging from annelids and arthropods to mammals are providing evidence that corresponding developmental genetic mechanisms act not only in dorso–ventral and anterior–posterior axis specification but also in segmentation, neurogenesis, axogenesis and eye/photoreceptor cell formation that appear to be conserved throughout the animal kingdom. These data are supported by recent studies which identified Mid-Cambrian fossils with preserved soft body parts that present segmental arrangements in brains typical of modern arthropods, and similarly organized brain centres and circuits across phyla that may reflect genealogical correspondence and control similar behavioural manifestations. Moreover, congruence between genetic and geological fossil records support the notion that by the ‘Cambrian explosion’ arthropods and chordates shared similarities in brain and nervous system organization. However, these similarities are strikingly absent in several sister- and outgroups of arthropods and chordates which raises several questions, foremost among them: what kind of natural laws and mechanisms underlie the convergent evolution of such similarities? And, vice versa: what are the selection pressures and genetic mechanisms underlying the possible loss or reduction of brains and CNSs in multiple lineages during the course of evolution? These questions were addressed at a Royal Society meeting to discuss homology and convergence in nervous system evolution. By integrating knowledge ranging from evolutionary theory and palaeontology to comparative developmental genetics and phylogenomics, the meeting covered disparities in nervous system origins as well as correspondences of neural circuit organization and behaviours, all of which allow evidence-based debates for and against the proposition that the nervous systems and brains of animals might derive from a common ancestor.
• Strausfeld, N. J., & Wolff, G. H. (2016). Genealogical correspondence of a forebrain centre implies an executive brain in the protostome–deuterostome bilaterian ancestor. Philosophical Transactions of the Royal Society B: Biological Sciences, 371(1685), 20150055. doi:10.1098/rstb.2015.0055
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  Orthologous genes involved in the formation of proteins associated with memory acquisition are similarly expressed in forebrain centres that exhibit similar cognitive properties. These proteins include cAMP-dependent protein kinase A catalytic subunit (PKA-Cα) and phosphorylated Ca 2+ /calmodulin-dependent protein kinase II (pCaMKII), both required for long-term memory formation which is enriched in rodent hippocampus and insect mushroom bodies, both implicated in allocentric memory and both possessing corresponding neuronal architectures. Antibodies against these proteins resolve forebrain centres, or their equivalents, having the same ground pattern of neuronal organization in species across five phyla. The ground pattern is defined by olfactory or chemosensory afferents supplying systems of parallel fibres of intrinsic neurons intersected by orthogonal domains of afferent and efferent arborizations with local interneurons providing feedback loops. The totality of shared characters implies a deep origin in the protostome–deuterostome bilaterian ancestor of elements of a learning and memory circuit. Proxies for such an ancestral taxon are simple extant bilaterians, particularly acoels that express PKA-Cα and pCaMKII in discrete anterior domains that can be properly referred to as brains.
• Strausfeld, N. J., Hejnol, A., Wolff, G. H., & Martín-Durán, J. M. (2016). The larval nervous system of the penis wormPriapulus caudatus(Ecdysozoa). Philosophical Transactions of the Royal Society B. doi:https://doi.org/10.1098/rstb.2015.0050
• Strausfeld, N. J., Hou, X., Cong, P., Liu, Y., Land, M. F., Fortey, R. A., Edgecombe, G. D., & Ma, X. (2016). Arthropod eyes: The early Cambrian fossil record and divergent evolution of visual systems. Arthropod Structure & Development. doi:10.1016/j.asd.2015.07.005
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  Four types of eyes serve the visual neuropils of extant arthropods: compound retinas composed of adjacent facets; a visual surface populated by spaced eyelets; a smooth transparent cuticle providing inwardly directed lens cylinders; and single-lens eyes. The first type is a characteristic of pancrustaceans, the eyes of which comprise lenses arranged as hexagonal or rectilinear arrays, each lens crowning 8-9 photoreceptor neurons. Except for Scutigeromorpha, the second type typifies Myriapoda whose relatively large eyelets surmount numerous photoreceptive rhabdoms stacked together as tiers. Scutigeromorph eyes are facetted, each lens crowning some dozen photoreceptor neurons of a modified apposition-type eye. Extant chelicerate eyes are single-lensed except in xiphosurans, whose lateral eyes comprise a cuticle with a smooth outer surface and an inner one providing regular arrays of lens cylinders. This account discusses whether these disparate eye types speak for or against divergence from one ancestral eye type. Previous considerations of eye evolution, focusing on the eyes of trilobites and on facet proliferation in xiphosurans and myriapods, have proposed that the mode of development of eyes in those taxa is distinct from that of pancrustaceans and is the plesiomorphic condition from which facetted eyes have evolved. But the recent discovery of enormous regularly facetted compound eyes belonging to early Cambrian radiodontans suggests that high-resolution facetted eyes with superior optics may be the ground pattern organization for arthropods, predating the evolution of arthrodization and jointed post-protocerebral appendages. Here we provide evidence that compound eye organization in stem-group euarthropods of the Cambrian can be understood in terms of eye morphologies diverging from this ancestral radiodontan-type ground pattern. We show that in certain Cambrian groups apposition eyes relate to fixed or mobile eyestalks, whereas other groups reveal concomitant evolution of sessile eyes equipped with optics typical of extant xiphosurans. Observations of fossil material, including that of trilobites and eurypterids, support the proposition that the ancestral compound eye was the apposition type. Cambrian arthropods include possible precursors of mandibulate eyes. The latter are the modified compound eyes, now sessile, and their underlying optic lobes exemplified by scutigeromorph chilopods, and the mobile stalked compound eyes and more elaborate optic lobes typifying Pancrustacea. Radical divergence from an ancestral apposition type is demonstrated by the evolution of chelicerate eyes, from doublet sessile-eyed stem-group taxa to special apposition eyes of xiphosurans, the compound eyes of eurypterids, and single-lens eyes of arachnids. Different eye types are discussed with respect to possible modes of life of the extinct species that possessed them, comparing these to extant counterparts and the types of visual centers the eyes might have served.
• Strausfeld, N. J., Ma, X., & Edgecombe, G. D. (2016). Fossils and the Evolution of the Arthropod Brain.. Current biology : CB, 26(20), R989-R1000. doi:10.1016/j.cub.2016.09.012
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  The discovery of fossilized brains and ventral nerve cords in lower and mid-Cambrian arthropods has led to crucial insights about the evolution of their central nervous system, the segmental identity of head appendages and the early evolution of eyes and their underlying visual systems. Fundamental ground patterns of lower Cambrian arthropod brains and nervous systems correspond to the ground patterns of brains and nervous systems belonging to three of four major extant panarthropod lineages. These findings demonstrate the evolutionary stability of early neural arrangements over an immense time span. Here, we put these fossil discoveries in the context of evidence from cladistics, as well as developmental and comparative neuroanatomy, which together suggest that despite many evolved modifications of neuropil centers within arthropod brains and ganglia, highly conserved arrangements have been retained. Recent phylogenies of the arthropods, based on fossil and molecular evidence, and estimates of divergence dates, suggest that neural ground patterns characterizing onychophorans, chelicerates and mandibulates are likely to have diverged between the terminal Ediacaran and earliest Cambrian, heralding the exuberant diversification of body forms that account for the Cambrian Explosion.
• Edgecombe, G. D., Ma, X., & Strausfeld, N. J. (2015). Unlocking the early fossil record of the arthropod central nervous system. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 370(1684).
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  Extant panarthropods (euarthropods, onychophorans and tardigrades) are hallmarked by stunning morphological and taxonomic diversity, but their central nervous systems (CNS) are relatively conserved. The timing of divergences of the ground pattern CNS organization of the major panarthropod clades has been poorly constrained because of a scarcity of data from their early fossil record. Although the CNS has been documented in three-dimensional detail in insects from Cenozoic ambers, it is widely assumed that these tissues are too prone to decay to withstand other styles of fossilization or geologically older preservation. However, Cambrian Burgess Shale-type compressions have emerged as sources of fossilized brains and nerve cords. CNS in these Cambrian fossils are preserved as carbon films or as iron oxides/hydroxides after pyrite in association with carbon. Experiments with carcasses compacted in fine-grained sediment depict preservation of neural tissue for a more prolonged temporal window than anticipated by decay experiments in other media. CNS and compound eye characters in exceptionally preserved Cambrian fossils predict divergences of the mandibulate and chelicerate ground patterns by Cambrian Stage 3 (ca 518 Ma), a dating that is compatible with molecular estimates for these splits.
• Fiore, V. G., Dolan, R. J., Strausfeld, N. J., & Hirth, F. (2015). Evolutionarily conserved mechanisms for the selection and maintenance of behavioural activity. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 370(1684).
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  Survival and reproduction entail the selection of adaptive behavioural repertoires. This selection manifests as phylogenetically acquired activities that depend on evolved nervous system circuitries. Lorenz and Tinbergen already postulated that heritable behaviours and their reliable performance are specified by genetically determined programs. Here we compare the functional anatomy of the insect central complex and vertebrate basal ganglia to illustrate their role in mediating selection and maintenance of adaptive behaviours. Comparative analyses reveal that central complex and basal ganglia circuitries share comparable lineage relationships within clusters of functionally integrated neurons. These clusters are specified by genetic mechanisms that link birth time and order to their neuronal identities and functions. Their subsequent connections and associated functions are characterized by similar mechanisms that implement dimensionality reduction and transition through attractor states, whereby spatially organized parallel-projecting loops integrate and convey sensorimotor representations that select and maintain behavioural activity. In both taxa, these neural systems are modulated by dopamine signalling that also mediates memory-like processes. The multiplicity of similarities between central complex and basal ganglia suggests evolutionarily conserved computational mechanisms for action selection. We speculate that these may have originated from ancestral ground pattern circuitries present in the brain of the last common ancestor of insects and vertebrates.
• Ma, X., Edgecombe, G. D., Hou, X., Goral, T., & Strausfeld, N. J. (2015). Preservational Pathways of Corresponding Brains of a Cambrian Euarthropod. Current biology : CB, 25(22), 2969-75.
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  The record of arthropod body fossils is traceable back to the "Cambrian explosion," marked by the appearance of most major animal phyla. Exceptional preservation provides crucial evidence for panarthropod early radiation. However, due to limited representation in the fossil record of internal anatomy, particularly the CNS, studies usually rely on exoskeletal and appendicular morphology. Recent studies [1-3] show that despite extreme morphological disparities, euarthropod CNS evolution appears to have been remarkably conservative. This conclusion is supported by descriptions from Cambrian panarthropods of neural structures that contribute to understanding early evolution of nervous systems and resolving controversies about segmental homologies [4-12]. However, the rarity of fossilized CNSs, even when exoskeletons and appendages show high levels of integrity, brought into question data reproducibility because all but one of the aforementioned studies were based on single specimens [13]. Foremost among objections is the lack of taphonomic explanation for exceptional preservation of a tissue that some see as too prone to decay to be fossilized. Here we describe newly discovered specimens of the Chengjiang euarthropod Fuxianhuia protensa with fossilized brains revealing matching profiles, allowing rigorous testing of the reproducibility of cerebral structures. Their geochemical analyses provide crucial insights of taphonomic pathways for brain preservation, ranging from uniform carbon compressions to complete pyritization, revealing that neural tissue was initially preserved as carbonaceous film and subsequently pyritized. This mode of preservation is consistent with the taphonomic pathways of gross anatomy, indicating that no special mode is required for fossilization of labile neural tissue.
• Steinbrecht, A., & Strausfeld, N. (2015). Editorial. Arthropod structure & development, 45(1), 1.
• Strausfeld, N. J. (2015). Palaeontology: Clearing the Heads of Cambrian Arthropods. Current Biology. doi:10.1016/j.cub.2015.05.026
• Strausfeld, N. J. (2015). Palaeontology: Clearing the Heads of Cambrian Arthropods. Current biology : CB, 25(14), R616-8.
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  Understanding the identity of segments and the evolution of their appendages is a prime concern of arthropod evolution studies. This has been challenging for long extinct stem-groups. Now, Cambrian fossils offer insights that will help further evolutionary considerations.
• Strausfeld, N. J., & Hirth, F. (2015). Introduction to ‘Origin and evolution of the nervous system’. Philosophical Transactions of the Royal Society B: Biological Sciences, 370(1684), 20150033. doi:10.1098/rstb.2015.0033
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  In 1665, Robert Hooke demonstrated in Micrographia the power of the microscope and comparative observations, one of which revealed similarities between the arthropod and vertebrate eyes. Utilizing comparative observations, Saint-Hilaire in 1822 was the first to propose that the ventral nervous system of arthropods corresponds to the dorsal nervous system of vertebrates. Since then, studies on the origin and evolution of the nervous system have become inseparable from studies about Metazoan origins and the origins of organ systems. The advent of genome sequence data and, in turn, phylogenomics and phylogenetics have refined cladistics and expanded our understanding of Metazoan phylogeny. However, the origin and evolution of the nervous system is still obscure and many questions and problems remain. A recurrent problem is whether and to what extent sequence data provide reliable guidance for comparisons across phyla. Are genetic data congruent with the geological fossil records? How can we reconcile evolved character loss with phylogenomic records? And how informative are genetic data in relation to the specification of nervous system morphologies? These provide some of the background and context for a Royal Society meeting to discuss new data and concepts that might achieve insights into the origin and evolution of brains and nervous systems.
• Strausfeld, N. J., & Hirth, F. (2015). Introduction to 'Origin and evolution of the nervous system'. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 370(1684).
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  In 1665, Robert Hooke demonstrated in Micrographia the power of the microscope and comparative observations, one of which revealed similarities between the arthropod and vertebrate eyes. Utilizing comparative observations, Saint-Hilaire in 1822 was the first to propose that the ventral nervous system of arthropods corresponds to the dorsal nervous system of vertebrates. Since then, studies on the origin and evolution of the nervous system have become inseparable from studies about Metazoan origins and the origins of organ systems. The advent of genome sequence data and, in turn, phylogenomics and phylogenetics have refined cladistics and expanded our understanding of Metazoan phylogeny. However, the origin and evolution of the nervous system is still obscure and many questions and problems remain. A recurrent problem is whether and to what extent sequence data provide reliable guidance for comparisons across phyla. Are genetic data congruent with the geological fossil records? How can we reconcile evolved character loss with phylogenomic records? And how informative are genetic data in relation to the specification of nervous system morphologies? These provide some of the background and context for a Royal Society meeting to discuss new data and concepts that might achieve insights into the origin and evolution of brains and nervous systems.
• Strausfeld, N. J., & Wolff, G. H. (2015). Genealogical Correspondence of Mushroom Bodies across Invertebrate Phyla. Current Biology. doi:10.1016/j.cub.2014.10.049
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  Except in species that have undergone evolved loss, paired lobed centers referred to as "mushroom bodies" occur across invertebrate phyla. Unresolved is the question of whether these centers, which support learning and memory in insects, correspond genealogically or whether their neuronal organization suggests convergent evolution. Here, anatomical and immunohistological observations demonstrate that across phyla, mushroom body-like centers share a neuroanatomical ground pattern and proteins required for memory formation. Paired lobed or dome-like neuropils characterize the first brain segment (protocerebrum) of mandibulate and chelicerate arthropods and the nonganglionic brains of polychaete annelids, polyclad planarians, and nemerteans. Structural and cladistic analyses resolve an ancestral ground pattern common to all investigated taxa: chemosensory afferents supplying thousands of intrinsic neurons, the parallel processes of which establish orthogonal networks with feedback loops, modulatory inputs, and efferents. Shared ground patterns and their selective labeling with antisera against proteins required for normal mushroom body function in Drosophila are indicative of genealogical correspondence and thus an ancestral presence predating arthropod and lophotrochozoan origins. Implications of this are considered in the context of mushroom body function and early ecologies of ancestral bilaterians.
• Strausfeld, N. J., Goral, T., Hou, X., Edgecombe, G. D., & Ma, X. (2015). Preservational Pathways of Corresponding Brains of a Cambrian Euarthropod. Current Biology. doi:10.1016/j.cub.2015.09.063
• Strausfeld, N. J., Hansson, B. S., Wolff, G. H., Rybak, J., Harzsch, S., Koczan, S., & Tuchina, O. (2015). Central projections of antennular chemosensory and mechanosensory afferents in the brain of the terrestrial hermit crab (Coenobita clypeatus; Coenobitidae, Anomura). Frontiers in Neuroanatomy. doi:10.3389/fnana.2015.00094
• Strausfeld, N. J., Hirth, F., Dolan, R. J., & Fiore, V. G. (2015). Evolutionarily conserved mechanisms for the selection and maintenance of behavioural activity. Philosophical Transactions of the Royal Society B, 370(1684), 20150053. doi:10.1098/rstb.2015.0053
• Strausfeld, N. J., Ma, X., & Edgecombe, G. D. (2015). Unlocking the early fossil record of the arthropod central nervous system. Philosophical Transactions of the Royal Society B, 370(1684), 20150038. doi:10.1098/rstb.2015.0038
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  Extant panarthropods (euarthropods, onychophorans and tardigrades) are hallmarked by stunning morphological and taxonomic diversity, but their central nervous systems (CNS) are relatively conserved. The timing of divergences of the ground pattern CNS organization of the major panarthropod clades has been poorly constrained because of a scarcity of data from their early fossil record. Although the CNS has been documented in three-dimensional detail in insects from Cenozoic ambers, it is widely assumed that these tissues are too prone to decay to withstand other styles of fossilization or geologically older preservation. However, Cambrian Burgess Shale-type compressions have emerged as sources of fossilized brains and nerve cords. CNS in these Cambrian fossils are preserved as carbon films or as iron oxides/hydroxides after pyrite in association with carbon. Experiments with carcasses compacted in fine-grained sediment depict preservation of neural tissue for a more prolonged temporal window than anticipated by decay experiments in other media. CNS and compound eye characters in exceptionally preserved Cambrian fossils predict divergences of the mandibulate and chelicerate ground patterns by Cambrian Stage 3 (ca 518 Ma), a dating that is compatible with molecular estimates for these splits.
• Tuchina, O., Koczan, S., Harzsch, S., Rybak, J., Wolff, G., Strausfeld, N. J., & Hansson, B. S. (2015). Central projections of antennular chemosensory and mechanosensory afferents in the brain of the terrestrial hermit crab (Coenobita clypeatus; Coenobitidae, Anomura). Frontiers in neuroanatomy, 9, 94.
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  The Coenobitidae (Decapoda, Anomura, Paguroidea) is a taxon of hermit crabs that includes two genera with a fully terrestrial life style as adults. Previous studies have shown that Coenobitidae have evolved a sense of spatial odor localization that is behaviorally highly relevant. Here, we examined the central olfactory pathway of these animals by analyzing central projections of the antennular nerve of Coenobita clypeatus, combining backfilling of the nerve with dextran-coupled dye, Golgi impregnations and three-dimensional reconstruction of the primary olfactory center, the antennular lobe. The principal pattern of putative olfactory sensory afferents in C. clypeatus is in many aspects similar to what have been established for aquatic decapod crustaceans, such as the spiny lobster Panulirus argus. However, there are also obvious differences that may, or may not represent adaptations related to a terrestrial lifestyle. In C. clypeatus, the antennular lobe dominates the deutocerebrum, having more than one thousand allantoid-shaped subunits. We observed two distinct patterns of sensory neuron innervation: putative olfactory afferents from the aesthetascs either supply the cap/subcap region of the subunits or they extend through its full depth. Our data also demonstrate that any one sensory axon can supply input to several subunits. Putative chemosensory (non-aesthetasc) and mechanosensory axons represent a different pathway and innervate the lateral and median antennular neuropils. Hence, we suggest that the chemosensory input in C. clypeatus might be represented via a dual pathway: aesthetascs target the antennular lobe, and bimodal sensilla target the lateral antennular neuropil and median antennular neuropil. The present data is compared to related findings in other decapod crustaceans.
• Wolff, G. H., & Strausfeld, N. J. (2015). Genealogical correspondence of mushroom bodies across invertebrate phyla. Current biology : CB, 25(1), 38-44.
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  Except in species that have undergone evolved loss, paired lobed centers referred to as "mushroom bodies" occur across invertebrate phyla. Unresolved is the question of whether these centers, which support learning and memory in insects, correspond genealogically or whether their neuronal organization suggests convergent evolution. Here, anatomical and immunohistological observations demonstrate that across phyla, mushroom body-like centers share a neuroanatomical ground pattern and proteins required for memory formation. Paired lobed or dome-like neuropils characterize the first brain segment (protocerebrum) of mandibulate and chelicerate arthropods and the nonganglionic brains of polychaete annelids, polyclad planarians, and nemerteans. Structural and cladistic analyses resolve an ancestral ground pattern common to all investigated taxa: chemosensory afferents supplying thousands of intrinsic neurons, the parallel processes of which establish orthogonal networks with feedback loops, modulatory inputs, and efferents. Shared ground patterns and their selective labeling with antisera against proteins required for normal mushroom body function in Drosophila are indicative of genealogical correspondence and thus an ancestral presence predating arthropod and lophotrochozoan origins. Implications of this are considered in the context of mushroom body function and early ecologies of ancestral bilaterians.
• Cong, P., Ma, X., Hou, X., Edgecombe, G. D., & Strausfeld, N. J. (2014). Brain structure resolves the segmental affinity of anomalocaridid appendages. Nature, 513(7519), 538-42.
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  Despite being among the most celebrated taxa from Cambrian biotas, anomalocaridids (order Radiodonta) have provoked intense debate about their affinities within the moulting-animal clade that includes Arthropoda. Current alternatives identify anomalocaridids as either stem-group euarthropods, crown-group euarthropods near the ancestry of chelicerates, or a segmented ecdysozoan lineage with convergent similarity to arthropods in appendage construction. Determining unambiguous affinities has been impeded by uncertainties about the segmental affiliation of anomalocaridid frontal appendages. These structures are variably homologized with jointed appendages of the second (deutocerebral) head segment, including antennae and 'great appendages' of Cambrian arthropods, or with the paired antenniform frontal appendages of living Onychophora and some Cambrian lobopodians. Here we describe Lyrarapax unguispinus, a new anomalocaridid from the early Cambrian Chengjiang biota, southwest China, nearly complete specimens of which preserve traces of muscles, digestive tract and brain. The traces of brain provide the first direct evidence for the segmental composition of the anomalocaridid head and its appendicular organization. Carbon-rich areas in the head resolve paired pre-protocerebral ganglia at the origin of paired frontal appendages. The ganglia connect to areas indicative of a bilateral pre-oral brain that receives projections from the eyestalk neuropils and compound retina. The dorsal, segmented brain of L. unguispinus reinforces an alliance between anomalocaridids and arthropods rather than cycloneuralians. Correspondences in brain organization between anomalocaridids and Onychophora resolve pre-protocerebral ganglia, associated with pre-ocular frontal appendages, as characters of the last common ancestor of euarthropods and onychophorans. A position of Radiodonta on the euarthropod stem-lineage implies the transformation of frontal appendages to another structure in crown-group euarthropods, with gene expression and neuroanatomy providing strong evidence that the paired, pre-oral labrum is the remnant of paired frontal appendages.
• Cong, P., Ma, X., Hou, X., Edgecombe, G. D., & Strausfeld, N. J. (2014). Cong et al. reply. Nature, 516(7530), E3-4.
• Cong, P., Ma, X., Hou, X., Edgecombe, G., & Strausfeld, N. (2014). Brain structure resolves the segmental affinity of anomalocaridid appendages. Nature.
• Ito, K., Shinomiya, K., Ito, M., Armstrong, J. D., Boyan, G., Hartenstein, V., Harzsch, S., Heisenberg, M., Homberg, U., Jenett, A., Keshishian, H., Restifo, L. L., Rössler, W., Simpson, J. H., Strausfeld, N. J., Strauss, R., Vosshall, L. B., & , I. B. (2014). A systematic nomenclature for the insect brain. Neuron, 81(4), 755-65.
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  Despite the importance of the insect nervous system for functional and developmental neuroscience, descriptions of insect brains have suffered from a lack of uniform nomenclature. Ambiguous definitions of brain regions and fiber bundles have contributed to the variation of names used to describe the same structure. The lack of clearly determined neuropil boundaries has made it difficult to document precise locations of neuronal projections for connectomics study. To address such issues, a consortium of neurobiologists studying arthropod brains, the Insect Brain Name Working Group, has established the present hierarchical nomenclature system, using the brain of Drosophila melanogaster as the reference framework, while taking the brains of other taxa into careful consideration for maximum consistency and expandability. The following summarizes the consortium's nomenclature system and highlights examples of existing ambiguities and remedies for them. This nomenclature is intended to serve as a standard of reference for the study of the brain of Drosophila and other insects.
• Ma, X., Cong, P., Hou, X., Edgecombe, G. D., & Strausfeld, N. J. (2014). An exceptionally preserved arthropod cardiovascular system from the early Cambrian. Nature communications, 5, 3560.
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  The assumption that amongst internal organs of early arthropods only the digestive system withstands fossilization is challenged by the identification of brain and ganglia in early Cambrian fuxianhuiids and megacheirans from southwest China. Here we document in the 520-million-year-old Chengjiang arthropod Fuxianhuia protensa an exceptionally preserved bilaterally symmetrical organ system corresponding to the vascular system of extant arthropods. Preserved primarily as carbon, this system includes a broad dorsal vessel extending through the thorax to the brain where anastomosing branches overlap brain segments and supply the eyes and antennae. The dorsal vessel provides segmentally paired branches to lateral vessels, an arthropod ground pattern character, and extends into the anterior part of the abdomen. The addition of its vascular system to documented digestive and nervous systems resolves the internal organization of F. protensa as the most completely understood of any Cambrian arthropod, emphasizing complexity that had evolved by the early Cambrian.
• Martín-Durán, J. M., Wolff, G. H., Strausfeld, N. J., & Hejnol, A. (2016). The larval nervous system of the penis worm Priapulus caudatus (Ecdysozoa). Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 371(1685).
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  The origin and extreme diversification of the animal nervous system is a central question in biology. While most of the attention has traditionally been paid to those lineages with highly elaborated nervous systems (e.g. arthropods, vertebrates, annelids), only the study of the vast animal diversity can deliver a comprehensive view of the evolutionary history of this organ system. In this regard, the phylogenetic position and apparently conservative molecular, morphological and embryological features of priapulid worms (Priapulida) place this animal lineage as a key to understanding the evolution of the Ecdysozoa (i.e. arthropods and nematodes). In this study, we characterize the nervous system of the hatching larva and first lorica larva of the priapulid worm Priapulus caudatus by immunolabelling against acetylated and tyrosinated tubulin, pCaMKII, serotonin and FMRFamide. Our results show that a circumoral brain and an unpaired ventral nerve with a caudal ganglion characterize the central nervous system of hatching embryos. After the first moult, the larva attains some adult features: a neck ganglion, an introvert plexus, and conspicuous secondary longitudinal neurites. Our study delivers a neuroanatomical framework for future embryological studies in priapulid worms, and helps illuminate the course of nervous system evolution in the Ecdysozoa.
• Mu, L., Bacon, J. P., Ito, K., & Strausfeld, N. J. (2014). Responses of Drosophila giant descending neurons to visual and mechanical stimuli. The Journal of experimental biology, 217(Pt 12), 2121-9.
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  In Drosophila, the paired giant descending neurons (GDNs), also known as giant fibers, and the paired giant antennal mechanosensory descending neurons (GAMDNs), are supplied by visual and mechanosensory inputs. Both neurons have the largest cell bodies in the brain and both supply slender axons to the neck connective. The GDN axon thereafter widens to become the largest axon in the thoracic ganglia, supplying information to leg extensor and wing depressor muscles. The GAMDN axon remains slender, interacting with other descending neuron axons medially. GDN and GAMDN dendrites are partitioned to receive inputs from antennal mechanosensory afferents and inputs from the optic lobes. Although GDN anatomy has been well studied in Musca domestica, less is known about the Drosophila homolog, including electrophysiological responses to sensory stimuli. Here we provide detailed anatomical comparisons of the GDN and the GAMDN, characterizing their sensory inputs. The GDN showed responses to light-on and light-off stimuli, expanding stimuli that result in luminance decrease, mechanical stimulation of the antennae, and combined mechanical and visual stimulation. We show that ensembles of lobula columnar neurons (type Col A) and mechanosensory antennal afferents are likely responsible for these responses. The reluctance of the GDN to spike in response to stimulation confirms observations of the Musca GDN. That this reluctance may be a unique property of the GDN is suggested by comparisons with the GAMDN, in which action potentials are readily elicited by mechanical and visual stimuli. The results are discussed in the context of descending pathways involved in multimodal integration and escape responses.
• Steinbrecht, A., & Strausfeld, N. (2014). A letter from the Editors. Arthropod Structure and Development, 43(1), 1-.
• Strausfeld, N. (2014). Nick Strausfeld. Current biology : CB, 24(24), R1147-8.
• Strausfeld, N. J. (2014). “What” and “where” in sensory space: parallels between olfactory and visual perception. Flavour, 3(1), 1-1. doi:10.1186/2044-7248-3-s1-k8
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  The representation of odorants detected by ligand-specific olfactory receptor neurons targeting discrete anatomical units called olfactory glomeruli has been well document for two animal groups: vertebrates and insects. Odortypic maps have likewise been confirmed in specific second and third order brain centers in these taxa. However, there are two abiding problems that confront researchers studying olfactory processing and odor representation. The first pertains to marine crustaceans, in which any olfactory receptor neuron responds to a broad range of stimulants and supplies an olfactory lobe that is very differently organized from those of the sister group Insecta. The second relates, generally, to the question of how an odor source is located by an animal in its odor space: which circuits enable the coding of “where” as distinct from “what.” Research on insects, suggests that two additional modalities are required to determine an odor source. Yet in insects, as in crustaceans, there are blind taxa living in still environments that efficiently locate odor cues. Comparative anatomical studies on arachnids and flightless insects also suggest that invoking casting behaviors within upstream wind currents may not be sufficient to account for odor source detection. To fully appreciate the challenge offered by odorlocating systems we need to turn to visual processing where recent research has demonstrated that high order visual primitives are encoded in specific glomerular islets that together comprise the optic glomerular complex (OpGC). As in the antennal lobes of an insect, glomeruli of the OpGC are interconnected by elaborate arrangements of local interneurons. The outputs from the OpGC variously extend to premotor descending pathways, to the mushroom bodies, and to central brain areas. Neurons in visual neuropils that supply optic glomeruli are retinotopically organized; yet, because the axons of any one type of these neurons converge at a particular glomerulus, information about where the stimulus occurred in visual space is not represented. The OpGC therefore shares with antennal lobe’s olfactory glomerular complex a representation of stimulus properties but not a representation of where those properties occur in sensory space. The visual system does, however, contain a simple parallel system of neurons distinct from the OpGC that encodes “where,” not of any particular feature but of a salient feature. In my overview talk I will compare organization of olfactory representation across Arthopoda emphasizing similarities with the visual system, and consider how sensory representations may have evolved from a common ground pattern. I will ask whether a search image for a substrate, in which there is odortopic representation – as opposed to odortypic representation – might develop from the study of how other modalities are encoded in glomerular centers. Research supported by the AFRL (FA86511010001).
• Strausfeld, N. J. (2016). Waptia revisited: Intimations of behaviors. Arthropod structure & development.
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  The middle Cambrian taxon Waptia fieldensis offers insights into early evolution of sensory arrangements that may have supported a range of actions such as exploratory behavior, burrowing, scavenging, swimming, and escape, amongst others. Less elaborate than many modern pancrustaceans, specific features of Waptia that suggest a possible association with the pancrustacean evolutionary trajectory, include mandibulate mouthparts, a single pair of antennae, reflective triplets on the head comparable to ocelli, and traces of brain and optic lobes that conform to the pancrustacean ground pattern. This account revisits an earlier description of Waptia to further interpret the distribution of its overall morphology and receptor arrangements in the context of plausible behavioral repertoires.
• Strausfeld, N. J., & Hirth, F. (2016). Introduction to 'Homology and convergence in nervous system evolution'. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 371(1685).
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  The origin of brains and central nervous systems (CNSs) is thought to have occurred before the Palaeozoic era 540 Ma. Yet in the absence of tangible evidence, there has been continued debate whether today's brains and nervous systems derive from one ancestral origin or whether similarities among them are due to convergent evolution. With the advent of molecular developmental genetics and genomics, it has become clear that homology is a concept that applies not only to morphologies, but also to genes, developmental processes, as well as to behaviours. Comparative studies in phyla ranging from annelids and arthropods to mammals are providing evidence that corresponding developmental genetic mechanisms act not only in dorso-ventral and anterior-posterior axis specification but also in segmentation, neurogenesis, axogenesis and eye/photoreceptor cell formation that appear to be conserved throughout the animal kingdom. These data are supported by recent studies which identified Mid-Cambrian fossils with preserved soft body parts that present segmental arrangements in brains typical of modern arthropods, and similarly organized brain centres and circuits across phyla that may reflect genealogical correspondence and control similar behavioural manifestations. Moreover, congruence between genetic and geological fossil records support the notion that by the 'Cambrian explosion' arthropods and chordates shared similarities in brain and nervous system organization. However, these similarities are strikingly absent in several sister- and outgroups of arthropods and chordates which raises several questions, foremost among them: what kind of natural laws and mechanisms underlie the convergent evolution of such similarities? And, vice versa: what are the selection pressures and genetic mechanisms underlying the possible loss or reduction of brains and CNSs in multiple lineages during the course of evolution? These questions were addressed at a Royal Society meeting to discuss homology and convergence in nervous system evolution. By integrating knowledge ranging from evolutionary theory and palaeontology to comparative developmental genetics and phylogenomics, the meeting covered disparities in nervous system origins as well as correspondences of neural circuit organization and behaviours, all of which allow evidence-based debates for and against the proposition that the nervous systems and brains of animals might derive from a common ancestor.
• Strausfeld, N. J., Edgecombe, G. D., Hou, X., Cong, P., & Ma, X. (2014). An exceptionally preserved arthropod cardiovascular system from the early Cambrian. Nature Communications. doi:10.1038/ncomms4560
• Strausfeld, N. J., Edgecombe, G. D., Hou, X., Ma, X., & Cong, P. (2014). Brain structure resolves the segmental affinity of anomalocaridid appendages. Nature. doi:10.1038/nature13486
• Strausfeld, N. J., Edgecombe, G. D., Hou, X., Ma, X., & Cong, P. (2014). Cong et al. reply. Nature. doi:10.1038/nature13861
• Strausfeld, N. J., Ma, X., Edgecombe, G. D., Fortey, R. A., Land, M. F., Liu, Y., Cong, P., & Hou, X. (2016). Arthropod eyes: The early Cambrian fossil record and divergent evolution of visual systems. Arthropod structure & development.
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  Four types of eyes serve the visual neuropils of extant arthropods: compound retinas composed of adjacent facets; a visual surface populated by spaced eyelets; a smooth transparent cuticle providing inwardly directed lens cylinders; and single-lens eyes. The first type is a characteristic of pancrustaceans, the eyes of which comprise lenses arranged as hexagonal or rectilinear arrays, each lens crowning 8-9 photoreceptor neurons. Except for Scutigeromorpha, the second type typifies Myriapoda whose relatively large eyelets surmount numerous photoreceptive rhabdoms stacked together as tiers. Scutigeromorph eyes are facetted, each lens crowning some dozen photoreceptor neurons of a modified apposition-type eye. Extant chelicerate eyes are single-lensed except in xiphosurans, whose lateral eyes comprise a cuticle with a smooth outer surface and an inner one providing regular arrays of lens cylinders. This account discusses whether these disparate eye types speak for or against divergence from one ancestral eye type. Previous considerations of eye evolution, focusing on the eyes of trilobites and on facet proliferation in xiphosurans and myriapods, have proposed that the mode of development of eyes in those taxa is distinct from that of pancrustaceans and is the plesiomorphic condition from which facetted eyes have evolved. But the recent discovery of enormous regularly facetted compound eyes belonging to early Cambrian radiodontans suggests that high-resolution facetted eyes with superior optics may be the ground pattern organization for arthropods, predating the evolution of arthrodization and jointed post-protocerebral appendages. Here we provide evidence that compound eye organization in stem-group euarthropods of the Cambrian can be understood in terms of eye morphologies diverging from this ancestral radiodontan-type ground pattern. We show that in certain Cambrian groups apposition eyes relate to fixed or mobile eyestalks, whereas other groups reveal concomitant evolution of sessile eyes equipped with optics typical of extant xiphosurans. Observations of fossil material, including that of trilobites and eurypterids, support the proposition that the ancestral compound eye was the apposition type. Cambrian arthropods include possible precursors of mandibulate eyes. The latter are the modified compound eyes, now sessile, and their underlying optic lobes exemplified by scutigeromorph chilopods, and the mobile stalked compound eyes and more elaborate optic lobes typifying Pancrustacea. Radical divergence from an ancestral apposition type is demonstrated by the evolution of chelicerate eyes, from doublet sessile-eyed stem-group taxa to special apposition eyes of xiphosurans, the compound eyes of eurypterids, and single-lens eyes of arachnids. Different eye types are discussed with respect to possible modes of life of the extinct species that possessed them, comparing these to extant counterparts and the types of visual centers the eyes might have served.
• Strausfeld, N. J., Mu, L., Bacon, J. P., & Ito, K. (2014). Responses ofDrosophilagiant descending neurons to visual and mechanical stimuli. Journal of Experimental Biology. doi:10.1242/jeb.099135
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  Abstract In Drosophila, the paired Giant Descending Neurons (GDN), also known as Giant Fibers (GFs), and the paired Giant Antennal Mechanosensory Descending Neurons (GAMDN), are supplied by visual and mechanosensory inputs. Both neurons have the largest cell bodies in the brain and both supply slender axons to the neck connective. The GDN axon thereafter widens to become the largest axon in the thoracic ganglia, supplying information to leg extensor and wing depressor muscles. The GAMDN axon remains slender, interacting with other DN axons medially. GDN and GAMDN dendrites are partitioned to receive inputs from antennal mechanosensory afferents and inputs from the optic lobes. Although GDN anatomy has been well studied in Musca domestica, less is known about Drosophila homologue, including electrophysiological responses to sensory stimuli. Here we provide detailed anatomical comparisons of the GDN and the GAMDN, characterizing their sensory inputs. The GDN showed responses to light-ON and light-OFF stimuli, expanding stimuli that result in luminance decrease, mechanical stimulation of the antennae, and combined mechanical and visual stimulation. We show that ensembles of lobula columnar neurons (type Col A) and mechanosensory antennal afferents are likely responsible for these responses. The reluctance of the GDN to spike in response to stimulation confirms observations of the Musca GDN. That this reluctance may be a unique property of the GDN is suggested by comparisons with the GAMDN, in which action potentials are readily elicited by mechanical and visual stimuli. The results are discussed in the context of descending pathways involved in multimodal integration and escape responses.
• Strausfeld, N. J., Vosshall, L. B., Strauss, R., Simpson, J. A., Rössler, W., Restifo, L. L., Keshishian, H., Jenett, A., Homberg, U., Heisenberg, M., Harzsch, S., Hartenstein, V., Boyan, G., Armstrong, J. T., Ito, M., Shinomiya, K., & Ito, K. (2014). A Systematic Nomenclature for the Insect Brain. Neuron. doi:10.1016/j.neuron.2013.12.017
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  Despite the importance of the insect nervous system for functional and developmental neuroscience, descriptions of insect brains have suffered from a lack of uniform nomenclature. Ambiguous definitions of brain regions and fiber bundles have contributed to the variation of names used to describe the same structure. The lack of clearly determined neuropil boundaries has made it difficult to document precise locations of neuronal projections for connectomics study. To address such issues, a consortium of neurobiologists studying arthropod brains, the Insect Brain Name Working Group, has established the present hierarchical nomenclature system, using the brain of Drosophila melanogaster as the reference framework, while taking the brains of other taxa into careful consideration for maximum consistency and expandability. The following summarizes the consortium's nomenclature system and highlights examples of existing ambiguities and remedies for them. This nomenclature is intended to serve as a standard of reference for the study of the brain of Drosophila and other insects.
• Wolff, G. H., & Strausfeld, N. J. (2016). Genealogical correspondence of a forebrain centre implies an executive brain in the protostome-deuterostome bilaterian ancestor. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 371(1685).
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  Orthologous genes involved in the formation of proteins associated with memory acquisition are similarly expressed in forebrain centres that exhibit similar cognitive properties. These proteins include cAMP-dependent protein kinase A catalytic subunit (PKA-Cα) and phosphorylated Ca(2+)/calmodulin-dependent protein kinase II (pCaMKII), both required for long-term memory formation which is enriched in rodent hippocampus and insect mushroom bodies, both implicated in allocentric memory and both possessing corresponding neuronal architectures. Antibodies against these proteins resolve forebrain centres, or their equivalents, having the same ground pattern of neuronal organization in species across five phyla. The ground pattern is defined by olfactory or chemosensory afferents supplying systems of parallel fibres of intrinsic neurons intersected by orthogonal domains of afferent and efferent arborizations with local interneurons providing feedback loops. The totality of shared characters implies a deep origin in the protostome-deuterostome bilaterian ancestor of elements of a learning and memory circuit. Proxies for such an ancestral taxon are simple extant bilaterians, particularly acoels that express PKA-Cα and pCaMKII in discrete anterior domains that can be properly referred to as brains.
• Lin, C., & Strausfeld, N. J. (2013). A precocious adult visual center in the larva defines the unique optic lobe of the split-eyed whirligig beetle Dineutus sublineatus. Frontiers in Zoology, 10(1).
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  PMID: 23421712;PMCID: PMC3607853;Abstract: Introduction: Whirligig beetles (Coleoptera: Gyrinidae) are aquatic insects living on the water surface. They are equipped with four compound eyes, an upper pair viewing above the water surface and a lower submerged pair viewing beneath the water surface, but little is known about how their visual brain centers (optic lobes) are organized to serve such unusual eyes. We show here, for the first time, the peculiar optic lobe organization of the larval and adult whirligig beetle Dineutus sublineatus.Results: The divided compound eyes of adult whirligig beetles supply optic lobes that are split into two halves, an upper half and lower half, comprising an upper and lower lamina, an upper and lower medulla and a bilobed partially split lobula. However, the lobula plate, a neuropil that in flies is known to be involved in mediating stabilized flight, exists only in conjunction with the lower lobe of the lobula. We show that, as in another group of predatory beetle larvae, in the whirligig beetle the aquatic larva precociously develops a lobula plate equipped with wide-field neurons. It is supplied by three larval laminas serving the three dorsal larval stemmata, which are adjacent to the developing upper compound eye.Conclusions: In adult whirligig beetles, dual optic neuropils serve the upper aerial eyes and the lower subaquatic eyes. The exception is the lobula plate. A lobula plate develops precociously in the larva where it is supplied by inputs from three larval stemmata that have a frontal-upper field of view, in which contrasting objects such as prey items trigger a body lunge and mandibular grasp. This precocious lobula plate is lost during pupal metamorphosis, whereas another lobula plate develops normally during metamorphosis and in the adult is associated with the lower eye. The different roles of the upper and lower lobula plates in supporting, respectively, larval predation and adult optokinetic balance are discussed. Precocious development of the upper lobula plate represents convergent evolution of an ambush hunting lifestyle, as exemplified by the terrestrial larvae of tiger beetles (Cicindelinae), in which activation of neurons in their precocious lobula plates, each serving two large larval stemmata, releases reflex body extension and mandibular grasp. © 2013 Lin and Strausfeld; licensee BioMed Central Ltd.
• Lin, C., & Strausfeld, N. J. (2013). A precocious adult visual center in the larva defines the unique optic lobe of the split-eyed whirligig beetle Dineutus sublineatus. Frontiers in zoology, 10(1), 7.
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  Whirligig beetles (Coleoptera: Gyrinidae) are aquatic insects living on the water surface. They are equipped with four compound eyes, an upper pair viewing above the water surface and a lower submerged pair viewing beneath the water surface, but little is known about how their visual brain centers (optic lobes) are organized to serve such unusual eyes. We show here, for the first time, the peculiar optic lobe organization of the larval and adult whirligig beetle Dineutus sublineatus.
• Strausfeld, N. J., & Hirth, F. (2013). Deep Homology of Arthropod Central Complex and Vertebrate Basal Ganglia. Science. doi:10.1126/science.1231828
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  Of Flies and Men Similarities of brain structure, function, and behavior are usually ascribed to convergent evolution. In their review, Strausfeld and Hirth (p. 157 ) identify multiple commonalities shared by vertebrate basal ganglia and a system of forebrain centers in arthropods called the central complex. The authors conclude that circuits essential to behavioral choice originated very early across phyla.
• Strausfeld, N. J., & Hirth, F. (2013). Deep homology of arthropod central complex and vertebrate basal ganglia. Science (New York, N.Y.), 340(6129), 157-61.
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  The arthropod central complex and vertebrate basal ganglia derive from embryonic basal forebrain lineages that are specified by an evolutionarily conserved genetic program leading to interconnected neuropils and nuclei that populate the midline of the forebrain-midbrain boundary region. In the substructures of both the central complex and basal ganglia, network connectivity and neuronal activity mediate control mechanisms in which inhibitory (GABAergic) and modulatory (dopaminergic) circuits facilitate the regulation and release of adaptive behaviors. Both basal ganglia and central complex dysfunction result in behavioral defects including motor abnormalities, impaired memory formation, attention deficits, affective disorders, and sleep disturbances. The observed multitude of similarities suggests deep homology of arthropod central complex and vertebrate basal ganglia circuitries underlying the selection and maintenance of behavioral actions.
• Strausfeld, N. J., & Hirth, F. (2013). Homology versus Convergence in Resolving Transphyletic Correspondences of Brain Organization. Brain Behavior and Evolution. doi:10.1159/000356102
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  Due to the largely absent fossil record, phylogenetic comparisons of brain structures rely on the analysis of nervous systems in extant taxa, many of which appear to have distinctive and dissimilar neural arrangements. The use of a multitude of comparative criteria, including developmental genetics, phylogenomics and neural circuit architecture, has recently resolved a highly conserved structural and functional ground pattern organization in the arthropod central complex and vertebrate basal ganglia. The minuteness of resemblance is exemplified by orthologous action selection circuits that are formed by homologous gene networks and which can lead to similar pathologies and behavioral disorders. It has been argued, however, that these similarities of brain centers can only be due to convergent evolution. What is still missing is a plausible scenario to explain how convergence could result in such a multitude of similarities and minuteness of resemblances, including gene expression, functional attributes and pathologies. In contrast, homology by common descent is the more parsimonious explanation. Moreover, the divergent elaboration of arthropod central complex and vertebrate basal ganglia does not obscure their shared ground pattern organization and thus genealogical correspondence.
• Strausfeld, N. J., & Hirth, F. (2013). Homology versus convergence in resolving transphyletic correspondences of brain organization. Brain, behavior and evolution, 82(4), 215-9.
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  Due to the largely absent fossil record, phylogenetic comparisons of brain structures rely on the analysis of nervous systems in extant taxa, many of which appear to have distinctive and dissimilar neural arrangements. The use of a multitude of comparative criteria, including developmental genetics, phylogenomics and neural circuit architecture, has recently resolved a highly conserved structural and functional ground pattern organization in the arthropod central complex and vertebrate basal ganglia. The minuteness of resemblance is exemplified by orthologous action selection circuits that are formed by homologous gene networks and which can lead to similar pathologies and behavioral disorders. It has been argued, however, that these similarities of brain centers can only be due to convergent evolution. What is still missing is a plausible scenario to explain how convergence could result in such a multitude of similarities and minuteness of resemblances, including gene expression, functional attributes and pathologies. In contrast, homology by common descent is the more parsimonious explanation. Moreover, the divergent elaboration of arthropod central complex and vertebrate basal ganglia does not obscure their shared ground pattern organization and thus genealogical correspondence.
• Strausfeld, N. J., & Lin, C. (2013). A precocious adult visual center in the larva defines the unique optic lobe of the split-eyed whirligig beetle Dineutus sublineatus. Frontiers in Zoology. doi:10.1186/1742-9994-10-7
• Strausfeld, N. J., Edgecombe, G. D., Ma, X., Hou, X., & Tanaka, G. (2013). Chelicerate neural ground pattern in a Cambrian great appendage arthropod. Nature. doi:10.1038/nature12520
• Tanaka, G., Hou, X., Ma, X., Edgecombe, G. D., & Strausfeld, N. J. (2013). Chelicerate neural ground pattern in a Cambrian great appendage arthropod. Nature, 502(7471), 364-7.
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  Preservation of neural tissue in early Cambrian arthropods has recently been demonstrated, to a degree that segmental structures of the head can be associated with individual brain neuromeres. This association provides novel data for addressing long-standing controversies about the segmental identities of specialized head appendages in fossil taxa. Here we document neuroanatomy in the head and trunk of a 'great appendage' arthropod, Alalcomenaeus sp., from the Chengjiang biota, southwest China, providing the most complete neuroanatomical profile known from a Cambrian animal. Micro-computed tomography reveals a configuration of one optic neuropil separate from a protocerebrum contiguous with four head ganglia, succeeded by eight contiguous ganglia in an eleven-segment trunk. Arrangements of optic neuropils, the brain and ganglia correspond most closely to the nervous system of Chelicerata of all extant arthropods, supporting the assignment of 'great appendage' arthropods to the chelicerate total group. The position of the deutocerebral neuromere aligns with the insertion of the great appendage, indicating its deutocerebral innervation and corroborating a homology between the 'great appendage' and chelicera indicated by morphological similarities. Alalcomenaeus and Fuxianhuia protensa demonstrate that the two main configurations of the brain observed in modern arthropods, those of Chelicerata and Mandibulata, respectively, had evolved by the early Cambrian.
• Andrew, D. R., Brown, S. M., & Strausfeld, N. J. (2012). The minute brain of the copepod tigriopus californicus supports a complex ancestral ground pattern of the tetraconate cerebral nervous systems. Journal of Comparative Neurology, 520(15), 3446-3470.
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  PMID: 22431149;Abstract: Copepods are a diverse and ecologically crucial group of minute crustaceans that are relatively neglected in terms of studies on nervous system organization. Recently, morphological neural characters have helped clarify evolutionary relationships within Arthropoda, particularly among Tetraconata (i.e., crustaceans and hexapods), and indicate that copepods occupy an important phylogenetic position relating to both Malacostraca and Hexapoda. This taxon therefore provides the opportunity to evaluate those neural characters common to these two clades likely to be results of shared ancestry (homology) versus convergence (homoplasy). Here we present an anatomical characterization of the brain and central nervous system of the well-studied harpacticoid copepod species Tigriopus californicus. We show that this species is endowed with a complex brain possessing a central complex comprising a protocerebral bridge and central body. Deutocerebral glomeruli are supplied by the antennular nerves, and a lateral protocerebral olfactory neuropil corresponds to the malacostracan hemiellipsoid body. Glomeruli contain synaptic specializations comparable to the presynaptic "T-bars" typical of dipterous insects, including Drosophila melanogaster. Serotonin-like immunoreactivity pervades the brain and ventral nervous system, with distinctive deutocerebral distributions. The present observations suggest that a suite of morphological characters typifying the Tigriopus brain reflect a ground pattern organization of an ancestral Tetraconata, which possessed an elaborate and structurally differentiated nervous system. © 2012 Wiley Periodicals, Inc.
• Brown, S., Strausfeld, N. J., Hansson, B. S., Harzsch, S., & Wolff, G. H. (2012). Neuronal organization of the hemiellipsoid body of the land hermit crab, Coenobita clypeatus: Correspondence with the mushroom body ground pattern. Journal of comparative neurology. doi:10.1002/cne.23059
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  Malacostracan crustaceans and dicondylic insects possess large second-order olfactory neuropils called, respectively, hemiellipsoid bodies and mushroom bodies. Because these centers look very different in the two groups of arthropods, it has been debated whether these second-order sensory neuropils are homologous or whether they have evolved independently. Here we describe the results of neuroanatomical observations and experiments that resolve the neuronal organization of the hemiellipsoid body in the terrestrial Caribbean hermit crab, Coenobita clypeatus, and compare this organization with the mushroom body of an insect, the cockroach Periplaneta americana. Comparisons of the morphology, ultrastructure, and immunoreactivity of the hemiellipsoid body of C. clypeatus and the mushroom body of the cockroach P. americana reveal in both a layered motif provided by rectilinear arrangements of extrinsic and intrinsic neurons as well as a microglomerular organization. Furthermore, antibodies raised against DC0, the major catalytic subunit of protein kinase A, specifically label both the crustacean hemiellipsoid bodies and insect mushroom bodies. In crustaceans lacking eyestalks, where the entire brain is contained within the head, this antibody selectively labels hemiellipsoid bodies, the superior part of which approximates a mushroom body's calyx in having large numbers of microglomeruli. We propose that these multiple correspondences indicate homology of the crustacean hemiellipsoid body and insect mushroom body and discuss the implications of this with respect to the phylogenetic history of arthropods. We conclude that crustaceans, insects, and other groups of arthropods share an ancestral neuronal ground pattern that is specific to their second-order olfactory centers.
• Lin, C., & Strausfeld, N. J. (2012). Visual inputs to the mushroom body calyces of the whirligig beetle Dineutus sublineatus: Modality switching in an insect. Journal of Comparative Neurology, 520(12), 2562-2574.
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  PMID: 22684942;Abstract: The mushroom bodies are prominent lobed centers in the forebrain, or protocerebrum, of most insects. Previous studies on mushroom bodies have focused on higher olfactory processing, including olfactory-based learning and memory. Anatomical studies provide strong support that in terrestrial insects with mushroom bodies, the primary input region, or calyces, are predominantly supplied by olfactory projection neurons from the antennal lobe glomeruli. In aquatic species that generally lack antennal lobes, the calyces are vestigial or absent. Here we report an exception to this in the whirligig beetle Dineutus sublineatus (Coleoptera: Gyrinidae). This aquatic species lives on water and is equipped with two separate pairs of compound eyes, one pair viewing above and one viewing below the water surface. As in other aquatic insects, the whirligig beetle lacks antennal lobes, but unlike other aquatic insects its mushroom bodies possess robust calyces. Golgi impregnations and fluorescent tracer injections revealed that the calyces are exclusively supplied by visual neurons from the medulla of the dorsal eye optic lobes. No other sensory inputs reach the calyces, thereby showing a complete switch of calyx modality from olfaction to vision. Potential functions of the mushroom bodies of D. sublineatus are discussed in the context of the behavioral ecology of whirligig beetles. © 2012 Wiley Periodicals, Inc.
• Ma, X., Hou, X., Edgecombe, G. D., & Strausfeld, N. J. (2012). Complex brain and optic lobes in an early Cambrian arthropod. Nature, 490(7419), 258-261.
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  PMID: 23060195;Abstract: The nervous system provides a fundamental source of data for understanding the evolutionary relationships between major arthropod groups. Fossil arthropods rarely preserve neural tissue. As a result, inferring sensory and motor attributes of Cambrian taxa has been limited to interpreting external features, such as compound eyes or sensilla decorating appendages, and early-diverging arthropods have scarcely been analysed in the context of nervous system evolution. Here we report exceptional preservation of the brain and optic lobes of a stem-group arthropod from 520 million years ago (Myr ago), Fuxianhuia protensa, exhibiting the most compelling neuroanatomy known from the Cambrian. The protocerebrum of Fuxianhuia is supplied by optic lobes evidencing traces of three nested optic centres serving forward-viewing eyes. Nerves from uniramous antennae define the deutocerebrum, and a stout pair of more caudal nerves indicates a contiguous tritocerebral component. Fuxianhuia shares a tripartite pre-stomodeal brain and nested optic neuropils with extant Malacostraca and Insecta, demonstrating that these characters were present in some of the earliest derived arthropods. The brain of Fuxianhuia impacts molecular analyses that advocate either a branchiopod-like ancestor of Hexapoda or remipedes and possibly cephalocarids as sister groups of Hexapoda. Resolving arguments about whether the simple brain of a branchiopod approximates an ancestral insect brain or whether it is the result of secondary simplification has until now been hindered by lack of fossil evidence. The complex brain of Fuxianhuia accords with cladistic analyses on the basis of neural characters, suggesting that Branchiopoda derive from a malacostracan-like ancestor but underwent evolutionary reduction and character reversal of brain centres that are common to hexapods and malacostracans. The early origin of sophisticated brains provides a probable driver for versatile visual behaviours, a view that accords with compound eyes from the early Cambrian that were, in size and resolution, equal to those of modern insects and malacostracans. © 2012 Macmillan Publishers Limited. All rights reserved.
• Mu, L., Ito, K., Bacon, J. P., & Strausfeld, N. J. (2012). Optic glomeruli and their inputs in Drosophila share an organizational ground pattern with the antennal lobes. Journal of Neuroscience, 32(18), 6061-6071.
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  PMID: 22553013;PMCID: PMC3358351;Abstract: Studying the insect visual system provides important data on the basic neural mechanisms underlying visual processing. As in vertebrates, the first step in visual processing in insects is through a series of retinotopic neurons. Recent studies on flies have found that these converge onto assemblies of columnar neurons in the lobula, the axons of which segregate to project to discrete optic glomeruli in the lateral protocerebrum. This arrangement is much like the fly's olfactory system, in which afferents target uniquely identifiable olfactory glomeruli. Here, whole-cell patch recordings show that even though visual primitives are unreliably encoded by single lobula output neurons because of high synaptic noise, they are reliably encoded by the ensemble of outputs. At a glomerulus, local inter neurons reliably code visual primitives, as do projection neurons conveying information centrally from the glomerulus. These observations demonstrate that in Drosophila, as in other dipterans, optic glomeruli are involved in further reconstructing the fly's visual world. Optic glomeruli and antennal lobe glomeruli share the same ancestral anatomical and functional ground pattern, enabling reliable responses to be extracted from converging sensory inputs. © 2012 the authors.
• Phillips-Portillo, J., & Strausfeld, N. J. (2012). Representation of the brain's superior protocerebrum of the flesh fly, Neobellieria bullata, in the central body. Journal of Comparative Neurology, 520(14), 3070-3087.
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  PMID: 22434505;Abstract: The central complex of the insect brain is a system of midline neuropils involved in transforming sensory information into behavioral outputs. Genetic studies focusing on nerve cells supplying the central complex from the protocerebrum propose that such neurons play key roles in circuits involved in learning the distinction of visual cues during operant conditioning. To better identify the possible sites of such circuits we used Bodian and anti-synapsin staining to resolve divisions of the superior protocerebrum into discrete neuropils. Here we show that in the fly Neobellieria bullata, the superior protocerebrum is composed of at least five clearly defined regions that correspond to those identified in Drosophila melanogaster. Intracellular dye fills and Golgi impregnations resolve "tangential neurons" that have intricate systems of branches in two of these regions. The branches are elaborate, decorated with specializations indicative of pre- and postsynaptic sites. The tangentially arranged terminals of these neurons extend across characteristic levels of the central complex's fan-shaped body. In this and another blowfly species, we identify an asymmetric pair of neuropils situated deep in the fan-shaped body, called the asymmetric bodies because of their likely homology with similar elements in Drosophila. One of the pair of bodies receives collaterals from symmetric arrangements of tangential neuron terminals. Cobalt injections reveal that the superior protocerebrum is richly supplied with local interneurons that are likely participants in microcircuitry associated with the distal processes of tangential neurons. Understanding the morphologies and arrangements of these and other neurons is essential for correctly interpreting functional attributes of the central complex. © 2012 Wiley Periodicals, Inc.
• Steinbrecht, A., & Strausfeld, N. (2012). Letter from the Editors. Arthropod Structure and Development, 41(1), 1-.
• Strausfeld, N. J. (2012). Arthropod brains: evolution, functional elegance, and historical significance. Choice Reviews Online, 1-830. doi:10.5860/choice.49-5677
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• Strausfeld, N. J., & Lin, C. (2012). Visual inputs to the mushroom body calyces of the whirligig beetle Dineutus sublineatus: Modality switching in an insect. Journal of comparative neurology. doi:10.1002/cne.23158
• Strausfeld, N. J., & Phillips-Portillo, J. (2012). Representation of the brain's superior protocerebrum of the flesh fly, Neobellieria bullata, in the central body. Journal of comparative neurology. doi:10.1002/cne.23094
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  The central complex of the insect brain is a system of midline neuropils involved in transforming sensory information into behavioral outputs. Genetic studies focusing on nerve cells supplying the central complex from the protocerebrum propose that such neurons play key roles in circuits involved in learning the distinction of visual cues during operant conditioning. To better identify the possible sites of such circuits we used Bodian and anti-synapsin staining to resolve divisions of the superior protocerebrum into discrete neuropils. Here we show that in the fly Neobellieria bullata, the superior protocerebrum is composed of at least five clearly defined regions that correspond to those identified in Drosophila melanogaster. Intracellular dye fills and Golgi impregnations resolve "tangential neurons" that have intricate systems of branches in two of these regions. The branches are elaborate, decorated with specializations indicative of pre- and postsynaptic sites. The tangentially arranged terminals of these neurons extend across characteristic levels of the central complex's fan-shaped body. In this and another blowfly species, we identify an asymmetric pair of neuropils situated deep in the fan-shaped body, called the asymmetric bodies because of their likely homology with similar elements in Drosophila. One of the pair of bodies receives collaterals from symmetric arrangements of tangential neuron terminals. Cobalt injections reveal that the superior protocerebrum is richly supplied with local interneurons that are likely participants in microcircuitry associated with the distal processes of tangential neurons. Understanding the morphologies and arrangements of these and other neurons is essential for correctly interpreting functional attributes of the central complex.
• Strausfeld, N. J., Bacon, J. P., Ito, K., & Mu, L. (2012). Optic Glomeruli and Their Inputs in Drosophila Share an Organizational Ground Pattern with the Antennal Lobes. The Journal of Neuroscience. doi:10.1523/jneurosci.0221-12.2012
• Strausfeld, N. J., Brown, S. D., & Andrew, D. P. (2012). The minute brain of the copepod Tigriopus californicus supports a complex ancestral ground pattern of the tetraconate cerebral nervous systems. Journal of comparative neurology. doi:10.1002/cne.23099
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  Copepods are a diverse and ecologically crucial group of minute crustaceans that are relatively neglected in terms of studies on nervous system organization. Recently, morphological neural characters have helped clarify evolutionary relationships within Arthropoda, particularly among Tetraconata (i.e., crustaceans and hexapods), and indicate that copepods occupy an important phylogenetic position relating to both Malacostraca and Hexapoda. This taxon therefore provides the opportunity to evaluate those neural characters common to these two clades likely to be results of shared ancestry (homology) versus convergence (homoplasy). Here we present an anatomical characterization of the brain and central nervous system of the well-studied harpacticoid copepod species Tigriopus californicus. We show that this species is endowed with a complex brain possessing a central complex comprising a protocerebral bridge and central body. Deutocerebral glomeruli are supplied by the antennular nerves, and a lateral protocerebral olfactory neuropil corresponds to the malacostracan hemiellipsoid body. Glomeruli contain synaptic specializations comparable to the presynaptic "T-bars" typical of dipterous insects, including Drosophila melanogaster. Serotonin-like immunoreactivity pervades the brain and ventral nervous system, with distinctive deutocerebral distributions. The present observations suggest that a suite of morphological characters typifying the Tigriopus brain reflect a ground pattern organization of an ancestral Tetraconata, which possessed an elaborate and structurally differentiated nervous system.
• Strausfeld, N. J., Edgecombe, G. D., Hou, X., & Ma, X. (2012). Complex brain and optic lobes in an early Cambrian arthropod. Nature. doi:10.1038/nature11495
• Wolff, G., Harzsch, S., Hansson, B. S., Brown, S., & Strausfeld, N. (2012). Neuronal organization of the hemiellipsoid body of the land hermit crab, Coenobita clypeatus: Correspondence with the mushroom body ground pattern. Journal of Comparative Neurology, 520(13), 2824-2846.
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  PMID: 22547177;Abstract: Malacostracan crustaceans and dicondylic insects possess large second-order olfactory neuropils called, respectively, hemiellipsoid bodies and mushroom bodies. Because these centers look very different in the two groups of arthropods, it has been debated whether these second-order sensory neuropils are homologous or whether they have evolved independently. Here we describe the results of neuroanatomical observations and experiments that resolve the neuronal organization of the hemiellipsoid body in the terrestrial Caribbean hermit crab, Coenobita clypeatus, and compare this organization with the mushroom body of an insect, the cockroach Periplaneta americana. Comparisons of the morphology, ultrastructure, and immunoreactivity of the hemiellipsoid body of C. clypeatus and the mushroom body of the cockroach P. americana reveal in both a layered motif provided by rectilinear arrangements of extrinsic and intrinsic neurons as well as a microglomerular organization. Furthermore, antibodies raised against DC0, the major catalytic subunit of protein kinase A, specifically label both the crustacean hemiellipsoid bodies and insect mushroom bodies. In crustaceans lacking eyestalks, where the entire brain is contained within the head, this antibody selectively labels hemiellipsoid bodies, the superior part of which approximates a mushroom body's calyx in having large numbers of microglomeruli. We propose that these multiple correspondences indicate homology of the crustacean hemiellipsoid body and insect mushroom body and discuss the implications of this with respect to the phylogenetic history of arthropods. We conclude that crustaceans, insects, and other groups of arthropods share an ancestral neuronal ground pattern that is specific to their second-order olfactory centers. © 2012 Wiley Periodicals, Inc.
• Harzsch, S., Rieger, V., Krieger, J., Seefluth, F., Strausfeld, N. J., & Hansson, B. S. (2011). Transition from marine to terrestrial ecologies: Changes in olfactory and tritocerebral neuropils in land-living isopods. Arthropod Structure and Development, 40(3), 244-257.
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  PMID: 21641866;Abstract: In addition to the ancestors of insects, representatives of five lineages of crustaceans have colonized land. Whereas insects have evolved sensilla that are specialized to allow the detection of airborne odors and have evolved olfactory sensory neurons that recognize specific airborne ligands, there is so far little evidence for aerial olfaction in terrestrial crustaceans. Here we ask the question whether terrestrial Isopoda have evolved the neuronal substrate for the problem of detecting far-field airborne chemicals. We show that conquest of land of Isopoda has been accompanied by a radical diminution of their first antennae and a concomitant loss of their deutocerebral olfactory lobes and olfactory computational networks. In terrestrial isopods, but not their marine cousins, tritocerebral neuropils serving the second antenna have evolved radical modifications. These include a complete loss of the malacostracan pattern of somatotopic representation, the evolution in some species of amorphous lobes and in others lobes equipped with microglomeruli, and yet in others the evolution of partitioned neuropils that suggest modality-specific segregation of second antenna inputs. Evidence suggests that Isopoda have evolved, and are in the process of evolving, several novel solutions to chemical perception on land and in air. © 2011 Elsevier Ltd.
• Steinbrecht, A., & Strausfeld, N. (2011). A letter from the Editors. Arthropod Structure and Development, 40(1), 1-.
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  PMID: 21081179;
• Strausfeld, N. J. (2011). Brain homology: Dohrn of a new era?. Brain, Behavior and Evolution, 76(3-4), 165-167.
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  PMID: 21196694;
• Strausfeld, N. J. (2011). Some observations on the sensory organization of the crustaceomorph Waptia fieldensis Walcott. Palaeontographica Canadiana, 157-168.
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  Abstract: Observations of traces interpreted as cerebral ganglia in the Burgess Shale taxon Waptia fieldensis Walcott, suggest a substantial brain supplied by turreted compound eyes and a pair of uniramous head appendages equipped with three kinds of sensilla: short brush like extensions, reminiscent of asthetascs, and two species of longer setae, reminiscent of either mechanosensory structures or mixed mechano- and chemosensory sensilla typical of extant malacostracan crustaceans. Of considerable interest is the question whether already in the mid-Cambrian, stem crustaceomorph arthropods show a loss or reduction of the second pair of head appendages, a feature typifying the Insecta and the distantly related Myriapoda. W. fieldensis is suggestive of such reduction. Further, the sensory structures on its legs and telson suggest that sensory systems of this species were as elaborate as those of certain extant malacostracans, such as the phyllo-carids. The degree to which central ganglia might have been elaborated in arthropods that have gone extinct can, to some degree, be inferred from sensory distributions in fossils and comparisons with extant taxa. © 2011 Joint Committee on Paleontological Monographs for CSPG/GAC.
• Strausfeld, N. J., & Andrew, D. R. (2011). A new view of insect-crustacean relationships I. Inferences from neural cladistics and comparative neuroanatomy. Arthropod Structure and Development, 40(3), 276-288.
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  PMID: 21333750;Abstract: Traditional hypotheses regarding the relationships of the major arthropod lineages focus on suites of comparable characters, often those that address features of the exoskeleton. However, because of the enormous morphological variety among arthropods, external characters may lead to ambiguities of interpretation and definition, particularly when species have undergone evolutionary simplification and reversal. Here we present the results of a cladistic analysis using morphological characters associated with brains and central nervous systems, based on the evidence that cerebral organization is generally robust over geological time. Well-resolved, strongly supported phylogenies were obtained from a neuromorphological character set representing a variety of discrete neuroanatomical traits. Phylogenetic hypotheses from this analysis support many accepted relationships, including monophyletic Chelicerata, Myriapoda, and Hexapoda, paraphyletic Crustacea and the union of Hexapoda and Crustacea (Tetraconata). They also support Mandibulata (Myriapoda + Tetraconata). One problematic result, which can be explained by symplesiomorphies that are likely to have evolved in deep time, is the inability to resolve Onychophora as a taxon distinct from Arthropoda. Crucially, neuronal cladistics supports the heterodox conclusion that both Hexapoda and Malacostraca are derived from a common ancestor that possessed a suite of discrete neural centers comprising an elaborate brain. Remipedes and copepods, both resolved as basal to Branchiopoda share a neural ground pattern with Malacostraca. These findings distinguish Hexapoda (Insecta) from Branchiopoda, which is the sister group of the clade Malacostraca + Hexapoda. The present study resolves branchiopod crustaceans as descendents of an ancestor with a complex brain, which means that they have evolved secondary simplification and the loss or reduction of numerous neural systems. © 2011.
• Strausfeld, N. J., Hansson, B. S., Seefluth, F., Krieger, J. E., Rieger, V., & Harzsch, S. (2011). Transition from marine to terrestrial ecologies: Changes in olfactory and tritocerebral neuropils in land-living isopods. Arthropod Structure & Development. doi:10.1016/j.asd.2011.03.002
• Sinakevitch, I., Grau, Y., Strausfeld, N. J., & Birman, S. (2010). Dynamics of glutamatergic signaling in the mushroom body of young adult Drosophila. Neural Development, 5(1).
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  PMID: 20370889;PMCID: PMC3003247;Abstract: Background: The mushroom bodies (MBs) are paired brain centers located in the insect protocerebrum involved in olfactory learning and memory and other associative functions. Processes from the Kenyon cells (KCs), their intrinsic neurons, form the bulk of the MB's calyx, pedunculus and lobes. In young adult Drosophila, the last-born KCs extend their processes in the α/β lobes as a thin core (α/β cores) that is embedded in the surrounding matrix of other mature KC processes. A high level of L-glutamate (Glu) immunoreactivity is present in the α/β cores (α/βc) of recently eclosed adult flies. In a Drosophila model of fragile X syndrome, the main cause of inherited mental retardation, treatment with metabotropic Glu receptor (mGluR) antagonists can rescue memory deficits and MB structural defects.Results: To address the role of Glu signaling in the development and maturation of the MB, we have compared the time course of Glu immunoreactivity with the expression of various glutamatergic markers at various times, that is, 1 hour, 1 day and 10 days after adult eclosion. We observed that last-born α/βc KCs in young adult as well as developing KCs in late larva and at various pupal stages transiently express high level of Glu immunoreactivity in Drosophila. One day after eclosion, the Glu level was already markedly reduced in the α/βc neurons. Glial cell processes expressing glutamine synthetase and the Glu transporter dEAAT1 were found to surround the Glu-expressing KCs in very young adults, subsequently enwrapping the α/β lobes to become distributed equally over the entire MB neuropil. The vesicular Glu transporter DVGluT was detected by immunostaining in processes that project within the MB lobes and pedunculus, but this transporter is apparently never expressed by the KCs themselves. The NMDA receptor subunit dNR1 is widely expressed in the MB neuropil just after eclosion, but was not detected in the α/βc neurons. In contrast, we provide evidence that DmGluRA, the only Drosophila mGluR, is specifically expressed in Glu-accumulating cells of the MB α/βc immediately and for a short time after eclosion.Conclusions: The distribution and dynamics of glutamatergic markers indicate that newborn KCs transiently accumulate Glu at a high level in late pupal and young eclosed Drosophila, and may locally release this amino acid by a mechanism that would not involve DVGluT. At this stage, Glu can bind to intrinsic mGluRs abundant in the α/βc KCs, and to NMDA receptors in the rest of the MB neuropil, before being captured and metabolized in surrounding glial cells. This suggests that Glu acts as an autocrine or paracrine agent that contributes to the structural and functional maturation of the MB during the first hours of Drosophila adult life. © 2010 Sinakevitch et al; licensee BioMed Central Ltd.
• Steinbrecht, R. A., & Strausfeld, N. J. (2010). Preface. The seventh Special Issue of ASD: "The Fossil Record and Phylogeny of the Arthropoda".. Arthropod structure & development, 39(2-3), 71-.
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  PMID: 20152930;
• Brown, S., & Strausfeld, N. (2009). The effect of age on a visual learning task in the American cockroach. Learning and Memory, 16(3), 210-223.
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  PMID: 19237643;Abstract: Neuronal modifications that accompany normal aging occur in brain neuropils and might share commonalties across phyla including the most successful group, the Insecta. This study addresses the kinds of neuronal modifications associated with loss of memory that occur in the hemimetabolous insect Periplaneta americana. Among insects that display considerable longevity, the American cockroach lives up to 64 wk and reveals specific cellular alterations in its mushroom bodies, higher centers that have been shown to be associated with learning and memory. The present results describe a vision-based learning paradigm, based on a modified Barnes maze, that compares memory in young (10-wk old), middle-aged (30-wk old), and aged adults (50-wk old). We show that not only is the performance of this task during the 14 training trials significantly decremented in aged cockroaches, but that aged cockroaches show significant impairment in successfully completing a crucial test involving cue rotation. Light and electron microscopical examination of the brains of these different age groups reveal major changes in neuron morphology and synaptology in the mushroom body lobes, centers shown to underlie place memory in this taxon. © 2009 Cold Spring Harbor Laboratory Press.
• Strausfeld, N. J. (2009). Brain and Optic Lobes. Encyclopedia of Insects, 121-130.
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  Abstract: This chapter discusses different segments of brain and optical lobe. Brain includes neuropils of the subesophageal ganglion, which is composed of the fused ganglia from three postoral segmental neuromeres. These are located ventrally with respect to the digestive tract, as are ganglia of the thorax and abdomen. In most hemimetabolous insects, and in many aleopterans, the subesophageal ganglion is connected by paired circumesophageal commissures to the supraesophageal ganglion. In many crown taxa, the subesophageal and supraesophageal ganglia are fused, as is the case in honey bees or the fruit fly Drosophila melanogaster, which is the taxon used to summarize the major divisions of the brain. A consequence of fusion is that tracts of axons that would otherwise form the circumesophageal commissures are embedded within a contiguous neuropil. Further, the optic lobes of palaeopteran and neopteran insects consist of three retinotopic neuropils. These are the lamina, medulla, and lobula complex. In certain orders of insects, the lobula complex is divided into two separate neuropils: a lenticular lobula that is mainly composed of columnar neurons and a tectum-like lobula plate that is hallmarked by wide-field tangential neurons. However, in insects with an undivided lobula, deeper layers comprise tangential neurons that probably have the same functions as tangential neurons in the lobula plate. © 2009 Elsevier Inc. All rights reserved.
• Strausfeld, N. J. (2009). Brain organization and the origin of insects: An assessment. Proceedings of the Royal Society B: Biological Sciences, 276(1664), 1929-1937.
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  PMID: 19324805;PMCID: PMC2677239;Abstract: Within the Arthropoda, morphologies of neurons, the organization of neurons within neuropils and the occurrence of neuropils can be highly conserved and provide robust characters for phylogenetic analyses. The present paper reviews some features of insect and crustacean brains that speak against an entomostracan origin of the insects, contrary to received opinion. Neural organization in brain centres, comprising olfactory pathways, optic lobes and a central neuropil that is thought to play a cardinal role in multi-joint movement, support affinities between insects and malacostracan crustaceans. © 2009 The Royal Society.
• Strausfeld, N. J. (2009). Earlier days. Journal of Neurogenetics, 23(1-2), 11-14.
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  PMID: 19031328;
• Strausfeld, N. J., Sinakevitch, I., Brown, S. M., & Farris, S. M. (2009). Ground plan of the insect mushroom body: Functional and evolutionary implications. Journal of Comparative Neurology, 513(3), 265-291.
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  PMID: 19152379;Abstract: In most insects with olfactory glomeruli, each side of the brain possesses a mushroom body equipped with calyces supplied by olfactory projection neurons. Kenyon cells providing dendrites to the calyces supply a pedunculus and lobes divided into subdivisions supplying outputs to other brain areas. It is with reference to these components that most functional studies are interpreted. However, mushroom body structures are diverse, adapted to different ecologies, and likely to serve various functions. In insects whose derived life styles preclude the detection of airborne odorants, there is a loss of the antennal lobes and attenuation or loss of the calyces. Such taxa retain mushroom body lobes that are as elaborate as those of mushroom bodies equipped with calyces. Antennal lobe loss and calycal regression also typify taxa with short nonfeeding adults, in which olfaction is redundant. Examples are cicadas and mayflies, the latter representing the most basal lineage of winged insects. Mushroom bodies of another basal taxon, the Odonata, possess a remnant calyx that may reflect the visual ecology of this group. That mushroom bodies persist in brains of secondarily anosmic insects suggests that they play roles in higher functions other than olfaction. Mushroom bodies are not ubiquitous: the most basal living insects, the wingless Archaeognatha, possess glomerular antennal lobes but lack mushroom bodies, suggesting that the ability to process airborne odorants preceded the acquisition of mushroom bodies. Archaeognathan brains are like those of higher malacostracans, which lack mushroom bodies but have elaborate olfactory centers laterally in the brain. ©2009 Wiley-Liss, Inc.
• Strausfeld, N., & Reisenman, C. E. (2009). Dimorphic olfactory lobes in the arthropoda. Annals of the New York Academy of Sciences, 1170, 487-496.
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  PMID: 19686183;PMCID: PMC2801554;Abstract: Specialized olfactory lobe glomeruli relating to sexual or caste differences have been observed in at least five orders of insects, suggesting an early appearance of this trait in insect evolution. Dimorphism is not limited to nocturnal species, but occurs even in insects that are known to use vision for courtship. Other than a single description, there is no evidence for similar structures occurring in the Crustacea, suggesting that the evolution of dimorphic olfactory systems may typify terrestrial arthropods. © 2009 New York Academy of Sciences.
• Sztarker, J., Strausfeld, N., Andrew, D., & Tomsic, D. (2009). Neural organization of first optic neuropils in the littoral crab Hemigrapsus oregonensis and the semiterrestrial species Chasmagnathus granulatus. Journal of Comparative Neurology, 513(2), 129-150.
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  PMID: 19123235;Abstract: Crustaceans are among the most extensively distributed arthropods, occupying many ecologies and manifesting a great variety of compound eye optics; but in comparison with insects, relatively little is known about the organization and neuronal morphologies of their underlying optic neuropils. Most studies, which have been limited to descriptions of the first neuropil-the lamina-suggest that different species have approximately comparable cell types, However, such studies have been limited with regard to the types of neurons they identify and most omit their topographic relationships. It is also uncertain whether similarities, such as they are, are independent of visual ecologies. The present account describes and compares the morphologies and dispositions of monopolar and other efferent neurons as well as the organization of tangential and smaller centrifugal neurons in two grapsoid crabs, one from the South Atlantic, the other from the North Pacific. Because these species occupy significantly disparate ecologies we ask whether this might be reflected in differences of cell arrangements within the most peripheral levels of the visual system. The present study identifies such differences with respect to the organization of centrifugal neurons to the lamina. We also identify in both species neurons in the lamina that have hitherto not been identified in crustaceans and we draw specific comparisons between the layered organization of the grapsoid lamina and layered laminas of insects. © 2009 Wiley-Liss, Inc.
• Sinakevitch, I., Sjöholm, M., Hansson, B. S., & Strausfeld, N. J. (2008). Global and local modulatory supply to the mushroom bodies of the moth Spodoptera littoralis. Arthropod Structure and Development, 37(4), 260-272.
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  PMID: 18406668;Abstract: The moth Spodoptera littoralis, is a major pest of agriculture whose olfactory system is tuned to odorants emitted by host plants and conspecifics. As in other insects, the paired mushroom bodies are thought to play pivotal roles in behaviors that are elicited by contextual and multisensory signals, amongst which those of specific odors dominate. Compared with species that have elaborate behavioral repertoires, such as the honey bee Apis mellifera or the cockroach Periplaneta americana, the mushroom bodies of S. littoralis were originally viewed as having a simple cellular organization. This has been since challenged by observations of putative transmitters and neuromodulators. As revealed by immunocytology, the spodopteran mushroom bodies, like those of other taxa, are subdivided longitudinally into discrete neuropil domains. Such divisions are further supported by the present study, which also demonstrates discrete affinities to different mushroom body neuropils by antibodies raised against two putative transmitters, glutamate and γ-aminobutyric acid, and against three putative neuromodulatory substances: serotonin, A-type allatostatin, and tachykinin-related peptides. The results suggest that in addition to longitudinal divisions of the lobes, circuits in the calyces and lobes are likely to be independently modulated. © 2008 Elsevier Ltd. All rights reserved.
• Steinbrecht, A., & Strausfeld, N. (2008). PubMed Announcement. Arthropod Structure and Development, 37(1), 1-.
• Strausfeld, N. J., & Seyfarth, E. (2008). Johann Flögel (1834-1918) and the birth of comparative insect neuroanatomy and brain nomenclature. Arthropod Structure and Development, 37(5), 434-441.
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  PMID: 18541456;Abstract: Johann H.L. Flögel (1834-1918) was an amateur scientist and self-taught microscopist in Germany who 130 years ago pioneered comparative arthropod neuroanatomy. He was fascinated by innovations in optical instrumentation, and his meticulous studies of the insect supraoesophageal ganglia were the first to use serial sections and photomicrographs to characterize the architecture of circumscribed regions of brain tissue. Flögel recognized the interpretative power resulting from observations across various species, and his comparative study of 1878, in particular, provided a baseline for subsequent workers to evolve a secure nomenclature of insect brain structures. His contributions stand out from contemporary accounts by virtue of their disciplined descriptions and emphasis on identifying comparable elements in different taxa. Here we give a biographical sketch of his life and summarize his remarkable achievements. © 2008 Elsevier Ltd. All rights reserved.
• Douglass, J. K., & Strausfeld, N. J. (2007). Diverse speed response properties of motion sensitive neurons in the fly's optic lobe. Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology, 193(2), 233-247.
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  PMID: 17106704;Abstract: Speed and acceleration are fundamental components of visual motion that animals can use to interpret the world. Behavioral studies have established that insects discriminate speed largely independently of contrast and spatial frequency, and physiological recordings suggest that a subset of premotor descending neurons is in this sense speed-selective. Neural substrates and mechanisms of speed selectivity in insects, however, are unknown. Using blow flies Phaenicia sericata, intracellular recordings and dye-fills were obtained from medulla and lobula complex neurons which, though not necessarily speed-selective themselves, are positioned to participate in circuits that produce speed-selectivity in descending neurons. Stimulation with sinusoidally varied grating motion (0-200°/s) provided a range of instantaneous velocities and accelerations. The resulting speed response profiles are indicative of four distinct speed ranges, supporting the hypothesis that the spatiotemporal tuning of mid-level neurons contains sufficient diversity to account for the emergence of speed selectivity at the descending neuron level. This type of mechanism has been proposed to explain speed discrimination in both insects and mammals, but has seemed less likely for insects due to possible constraints on small brains. Two additional recordings are suggestive of acceleration-selectivity, a potentially useful visual capability that is of uncertain functional significance for arthropods. © 2006 Springer-Verlag.
• Lent, D. D., Pintér, M., & Strausfeld, N. J. (2007). Learning with half a brain. Developmental Neurobiology, 67(6), 740-751.
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  PMID: 17443821;Abstract: Since the 1970s, human subjects that have undergone corpus callosotomy have provided important insights into neural mechanisms of perception, memory, and cognition. The ability to test the function of each hemisphere independently of the other offers unique advantages for investigating systems that are thought to underlie cognition. However, such approaches have been limited to mammals. Here we describe comparable experiments on an insect brain to demonstrate learning-associated changes within one brain hemisphere. After training one half of their bisected brains, cockroaches learn to extend the antenna supplying that brain hemisphere towards an illuminated diode after this has been paired with an odor stimulus. The antenna supplying the naïve hemisphere shows no response. Cockroaches retain this ability for up to 24 h, during which, shortly after training, the mushroom body of the trained hemisphere alone undergoes specific post-translational alterations of microglomerular synaptic complexes in its calyces. © 2007 Wiley Periodicals, Inc.
• Okamura, J., & Strausfeld, N. J. (2007). Visual system of calliphorid flies: Motion- and orientation-sensitive visual interneurons supplying dorsal optic glomeruli. Journal of Comparative Neurology, 500(1), 189-208.
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  PMID: 17099892;Abstract: Intracellular recordings accompanied by dye fills were made from neurons associated with optic glomeruli in the lateral protocerebrum of the brain of the blowfly Phoenicia sericata. The present account describes the morphology of these cells and their electrophys-iological responses to oriented bar motion. The most dorsal glomeruli are each supplied by retinotopic efferent neurons that have restricted dendritic fields in the lobula and lobula plate of the optic lobes. Each of these lobula complex cells represents a morphologically identified type of neuron arranged as an ensemble that subtends the entire monocular visual field. Of the four recorded and filled efferent types, three were broadly tuned to the orientation of bar stimuli. At the level of optic glomeruli a relay neuron extending centrally from optic foci and a local interneuron that arborizes among glomeruli showed narrow tuning to oriented bar motion. The present results are discussed with respect to the behavioral significance of oriented motion discrimination by flies and other insects, and with respect to neuroanatomical data demonstrating the organization of deep visual neuropils. © 2006 Wiley-Liss, Inc.
• Rister, J., Pauls, D., Schnell, B., Ting, C., Lee, C., Sinakevitch, I., Morante, J., Strausfeld, N. J., Ito, K., & Heisenberg, M. (2007). Dissection of the Peripheral Motion Channel in the Visual System of Drosophila melanogaster. Neuron, 56(1), 155-170.
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  PMID: 17920022;Abstract: In the eye, visual information is segregated into modalities such as color and motion, these being transferred to the central brain through separate channels. Here, we genetically dissect the achromatic motion channel in the fly Drosophila melanogaster at the level of the first relay station in the brain, the lamina, where it is split into four parallel pathways (L1-L3, amc/T1). The functional relevance of this divergence is little understood. We now show that the two most prominent pathways, L1 and L2, together are necessary and largely sufficient for motion-dependent behavior. At high pattern contrast, the two pathways are redundant. At intermediate contrast, they mediate motion stimuli of opposite polarity, L2 front-to-back, L1 back-to-front motion. At low contrast, L1 and L2 depend upon each other for motion processing. Of the two minor pathways, amc/T1 specifically enhances the L1 pathway at intermediate contrast. L3 appears not to contribute to motion but to orientation behavior. © 2007 Elsevier Inc. All rights reserved.
• Steinbrecht, A., & Strausfeld, N. (2007). Editorial. Arthropod Structure and Development, 36(2), 103-.
• Strausfeld, N. J., & Okamura, J. (2007). Visual system of calliphorid flies: Organization of optic glomeruli and their lobula complex efferents. Journal of Comparative Neurology, 500(1), 166-188.
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  PMID: 17099891;Abstract: Reconstructions of silver-stained brains revealed 27 optic glomeruli that occupy a major volume of the lateral protocerebrum. Axons from different morphological types of columnar output neurons from the lobula complex sort out to specific glomeruli. Glomeruli are partially enwrapped by glial processes and are invaded by the dendrites and terminals of local interneurons that connect different glomeruli in a manner analogous to local interneurons in the antennal lobes. Each type of columnar neuron contributes to a palisade-like ensemble that extends across the whole or a circumscribed area of the retinotopic mosaic. A second class of outputs from the lobula comprises wide-field neurons, the dendrites of which interact with planar fields or column-like patches of retino-topic inputs from the medulla. These neurons also send their axons to optic glomeruli. Dye fills demonstrate that lobula complex neurons supplying glomeruli do not generally terminate directly on descending neurons. Local interneurons and projection neurons provide integrative circuitry within and among glomeruli. As exemplified by the anterior optic tubercle, optic glomeruli can also have elaborate internal architectures. The results are discussed with respect to the identification of motion- and orientation-selective neurons at the level of the lobula and lateral protocerebrum and with respect to the evolutionary implications raised by the existence of neural arrangements serving the compound eyes, which are organized like neuropils serving segmental ganglia equipped with appendages. © 2006 Wiley-Liss, Inc.
• Strausfeld, N. J., Sinakevitch, I., & Okamura, J. (2007). Organization of local interneurons in optic glomeruli of the dipterous visual system and comparisons with the antennal lobes. Developmental Neurobiology, 67(10), 1267-1288.
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  PMID: 17638381;Abstract: The lateral protocerebrum of the fly's brain is composed of a system of optic glomeruli, the organization of which compares to that of antennal lobe glomeruli. Each optic glomerulus receives converging axon terminals from a unique ensemble of optic lobe output neurons. Glomeruli are interconnected by systems of spiking and nonspiking local interneurons that are morphologically similar to diffuse and polarized local interneurons in the antennal lobes. GABA-like immunoreactive processes richly supply optic glomeruli, which are also invaded by processes originating from the midbrain and subesophageal ganglia. These arrangements support the suggestion that circuits amongst optic glomeruli refine and elaborate visual information carried by optic lobe outputs, relaying data to long-axoned neurons that extend to other parts of the central nervous system including thoracic ganglia. The representation in optic glomeruli of other modalities suggests that gating of visual information by other sensory inputs, a phenomenon documented from the recordings of descending neurons, could occur before the descending neuron dendrites. The present results demonstrate that future studies must consider the roles of other senses in visual processing. © 2007 Wiley Periodicals, Inc.
• Strausfeld, N., Okamura, J., & Strausfeld, N. J. (2007). Visual system of calliphorid flies: motion- and orientation-sensitive visual interneurons supplying dorsal optic glomeruli. The Journal of comparative neurology, 500(1).
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  Intracellular recordings accompanied by dye fills were made from neurons associated with optic glomeruli in the lateral protocerebrum of the brain of the blowfly Phaenicia sericata. The present account describes the morphology of these cells and their electrophysiological responses to oriented bar motion. The most dorsal glomeruli are each supplied by retinotopic efferent neurons that have restricted dendritic fields in the lobula and lobula plate of the optic lobes. Each of these lobula complex cells represents a morphologically identified type of neuron arranged as an ensemble that subtends the entire monocular visual field. Of the four recorded and filled efferent types, three were broadly tuned to the orientation of bar stimuli. At the level of optic glomeruli a relay neuron extending centrally from optic foci and a local interneuron that arborizes among glomeruli showed narrow tuning to oriented bar motion. The present results are discussed with respect to the behavioral significance of oriented motion discrimination by flies and other insects, and with respect to neuroanatomical data demonstrating the organization of deep visual neuropils.
• Brown, S. M., & Strausfeld, N. J. (2006). Development-dependent and -independent ubiquitin expression in divisions of the cockroach mushroom body. Journal of Comparative Neurology, 496(4), 556-571.
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  PMID: 16572433;Abstract: It has been proposed that the alpha and beta divisions of the mushroom bodies support intermediate and long-term memory whereas the gamma lobes support short-term memory. Here we investigate developmentally dependent versus developmentally independent alterations of mushroom body structure with special emphasis on its lobes. We show that in the cockroach mushroom bodies there are two types of plastic remodeling. One is developmental, in which episodic addition of new circuitry to the alpha and beta lobes is accomplished by newly born Kenyon cells. The second is revealed as a persistent alteration of structure within the gamma lobe. In the alpha/beta lobes, newly generated Kenyon cell axons extend glutamate-immunoreactive collaterals across layers of the axons of mature Kenyon cells. At specific times in each developmental episode (instar) these collaterals express ubiquitin, undergo localized degeneration, and are scavenged by glial cells. In contrast, the mature Kenyon cells that comprise the gamma lobe express detectable ubiquitin throughout each developmental episode. This pattern of ubiquitin expression suggests that the gamma lobe circuitry undergoes continuous modification independent of development. © 2006 Wiley-Liss, Inc.
• Sinakevitch, I., & Strausfeld, N. J. (2006). Comparison of octopamine-like immunoreactivity in the brains of the fruit fly and blow fly. Journal of Comparative Neurology, 494(3), 460-475.
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  PMID: 16320256;Abstract: A serum raised against conjugated octopamine reveals structurally comparable systems of perikarya and arborizations in protocerebral neuropils of two species of Diptera, Drosophila melanogaster and Phaenicia sericata; the latter is used extensively for electrophysiological studies of the optic lobes and their central projections. Clusters of cell bodies in the brain as well as midline perikarya provide octopamine-like immunoreactive processes to the optic lobes, circumscribed regions of the protocerebrum and the central complex, particularly the protocerebral bridge, fan-shaped body, and ellipsoid body. Ventral unpaired median somata provide immunoreactive processes within the subesophageal ganglion and tritocerebrum. Ascending neurites from these cells also supply the antennal lobe glomeruli, regions of the lateral protocerebrum, the mushroom body calyces, and the lobula complex. The mushroom body's γ lobes contain immunoreactive processes that originate from processes that arborize in the protocerebrum. The present observations are discussed with respect to similarities and differences between two species of Diptera, one of which has neurons large enough for intracellular penetrations. The results are also discussed with respect to recent studies on octopamine-immunoreactive organization in honey bees and cockroaches and the suggested roles of octopamine in sensory processing, learning, and memory. © 2005 Wiley-Liss, Inc.
• Sjöholm, M., Sinakevitch, I., Strausfeld, N. J., Ignell, R., & Hansson, B. S. (2006). Functional division of intrinsic neurons in the mushroom bodies of male Spodoptera littoralis revealed by antibodies against aspartate, taurine, FMRF-amide, Mas-allatotropin and DC0. Arthropod Structure and Development, 35(3), 153-168.
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  PMID: 18089067;Abstract: The aim of this study was to further reveal the organization of Kenyon cells in the mushroom body calyx and lobes of the male moth Spodoptera littoralis, by using immunocytochemical labeling. Subdivisions of the mushroom bodies were identified employing antisera raised against the amino acids taurine and aspartate, the neuropeptides FMRF-amide and Mas-allatotropin, and against the protein kinase A catalytic subunit DC0. These antisera have previously been shown to label subsets of Kenyon cells in other species. The present results show that the organization of the mushroom body lobes into discrete divisions, described from standard neuroanatomical methods, is confirmed by immunocytology and shown to be further elaborated. Anti-taurine labels the accessory Y-tract, the γ division of the lobes, and a thin subdivision of the most posterior component of the lobes. Aspartate antiserum labels the entire mushroom body. FMRF-amide-like immunolabeling is pronounced in the γ division and in the anterior perimeter of the α/β and α′/β′ divisions. Mas-allatotropin-like immunolabeling shows the opposite of FMRF-amide-like and taurine-like immunolabeling: the γ division and the accessory Y-system is immunonegative whereas strong labeling is seen in both the α/β and α′/β′ divisions. The present results agree with findings from other insects that mushroom bodies are anatomically divided into discrete parallel units. Functional and developmental implications of this organization are discussed. © 2006 Elsevier Ltd. All rights reserved.
• Steinbrecht, A., & Strausfeld, N. (2006). Arthropod Structure & Development: Editorial. Arthropod Structure and Development, 35(1), 1-.
• Steinbrecht, A., & Strausfeld, N. (2006). Editorial. Arthropod Structure and Development, 35(4), 207-.
• Strausfeld, N. J., Strausfeld, C. M., Loesel, R., Rowell, D., & Stowe, S. (2006). Arthropod phylogeny: Onychophoran brain organization suggests an archaic relationship with a chelicerate stem lineage. Proceedings of the Royal Society B: Biological Sciences, 273(1596), 1857-1866.
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  PMID: 16822744;PMCID: PMC1634797;Abstract: Neuroanatomical studies have demonstrated that the architecture and organization among neuropils are highly conserved within any order of arthropods. The shapes of nerve cells and their neuropilar arrangements provide robust characters for phylogenetic analyses. Such analyses so far have agreed with molecular phylogenies in demonstrating that entomostracans + malacostracans belong to a clade (Tetraconata) that includes the hexapods. However, relationships among what are considered to be paraphyletic groups or among the stem arthropods have not yet been satisfactorily resolved. The present parsimony analyses of independent neuroarchitectural characters from 27 arthropods and lobopods demonstrate relationships that are congruent with phylogenies derived from molecular studies, except for the status of the Onychophora. The present account describes the brain of the onychophoran Euperipatoides rowelli, demonstrating that the structure and arrangements of its neurons, cerebral neuropils and sensory centres are distinct from arrangements in the brains of mandibulates. Neuroanatomical evidence suggests that the organization of the onychophoran brain is similar to that of the brains of chelicerates. © 2006 The Royal Society.
• Strausfeld, N. J., Strausfeld, C. M., Stowe, S., Rowell, D., & Loesel, R. (2006). The organization and evolutionary implications of neuropils and their neurons in the brain of the onychophoran Euperipatoides rowelli. Arthropod Structure and Development, 35(3), 169-196.
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  PMID: 18089068;Abstract: This account describes the organization of the brain of the adult Euperipatoides rowelli, a member of the Onychophora or "velvet worms." The present account identifies three cerebral divisions, the first of which contains primary olfactory neuropils, visual neuropils, and brain regions that correspond anatomically to the mushroom bodies of annelids, chelicerates, myriapods, and insects. In common with the brains of many chelicerates, the onychophoran brain is supplied by many thousands of uniformly small basophilic perikarya. Other chelicerate-like features include mushroom body lobes that extend across the brain's midline, an unpaired arch-shaped midline neuropil, and visual pathways that supply midline neuropil and that of the mushroom bodies. These and other similarities with chelicerate brains are discussed in the context of arthropod evolution and with reference to recent molecular phylogenies. © 2006.
• Douglass, J. K., & Strausfeld, N. J. (2005). Sign-conserving amacrine neurons in the fly's external plexiform layer. Visual Neuroscience, 22(3), 345-358.
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  PMID: 16079009;Abstract: Amacrine cells in the external plexiform layer of the fly's lamina have been intracellulary recorded and dye-filled for the first time. The recordings demonstrate that like the lamina's short photoreceptors R1-R6, type 1 lamina amacrine neurons exhibit nonspiking, "sign-conserving" sustained depolarizations in response to illumination. This contrasts with the sign-inverting responses that typify first-order retinotopic relay neurons: monopolar cells L1-L5 and the T1 efferent neuron. The contrast frequency tuning of amacrine neurons is similar to that of photoreceptors and large lamina monopolar cells. Initial observations indicate that lamina amacrine receptive fields are also photoreceptor-like, suggesting either that their inputs originate from a small number of neighboring visual sampling units (VSUs), or that locally generated potentials decay rapidly with displacement. Lamina amacrines also respond to motion, and in one recording these responses were selective for the orientation of moving edges. This functional organization corresponds to the anatomy of amacrine cells, in which postsynaptic inputs from several neighboring photoreceptor endings are linked by a network of very thin distal processes. In this way, each VSU can receive convergent inputs from a surround of amacrine processes. This arrangement is well suited for relaying responses to local intensity fluctuations from neighboring VSUs to a central VSU where amacrines are known to be presynaptic to the dendrites of the T1 efferent. The T1 terminal converges at a deeper level with that of the L2 monopolar cell relaying from the same optic cartridge. Thus, the localized spatial responses and receptor-like temporal response properties of amacrines are consistent with possible roles in lateral inhibition, motion processing, or orientation processing. Copyright © 2005 Cambridge University.
• Pintér, M., Lent, D. D., & Strausfeld, N. J. (2005). Erratum: Memory consolidation and gene expression in Periplaneta americana (Learning and Memory (2005) 12 (30-38)). Learning and Memory, 12(2), 209-.
• Pintér, M., Lent, D. D., & Strausfeld, N. J. (2005). Memory consolidation and gene expression in Periplaneta americana. Learning and Memory, 12(1), 30-38.
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  PMID: 15647592;PMCID: PMC548493;Abstract: A unique behavioral paradigm has been developed for Periplaneta americana that assesses the timing and success of memory consolidation leading to long-term memory of visual-olfactory associations. The brains of trained and control animals, removed at the critical consolidation period, were screened by two-directional suppression subtractive hybridization. Screens identified neurobiologically relevant as well as novel genes that are differentially expressed at the consolidation phase of memory. The differential expression of six transcripts was confirmed with real-time RT-PCR experiments. There are mitochondrial DNA encoded transcripts among the up-regulated ones (COX, ATPase6). One of the confirmed down-regulated transcripts is RNA polymerase II largest subunit. The mitochondrial genes are of particular interest because mitochondria represent autonomous DNA at synapses. These transcripts will be used as one of several tools in the identification of neuronal circuits, such as in the mushroom bodies, that are implicated in memory consolidation.
• Sinakevitch, I., Niwa, M., & Strausfeld, N. J. (2005). Octopamine-like immunoreactivity in the honey bee and cockroach: Comparable organization in the brain and subesophageal ganglion. Journal of Comparative Neurology, 488(3), 233-254.
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  PMID: 15952163;Abstract: A serum raised against octopamine reveals in cockroaches and honey bees structurally comparable systems of perikarya and their extensive yet discrete systems of arborizations in neuropils. Numerous and prominent clusters of lateral cell bodies in the brain as well as many midline perikarya provide octopamine-like immunoreactive processes to circumscribed regions of the subesophageal ganglion, antennal lobe glomeruli, optic neuropils, and neuropils of the protocerebrum. There is dense octopaminergic innervation in the protocerebral bridge and ellipsoid body of the central complex. The antennal lobes are supplied by at least three octopamine-immunoreactive neurons. In contrast, the mushroom bodies show the fewest immunoreactive elements. In Apis a single axon supplies sparse immunoreactive processes to the calyces' basal ring, collar, and lip. A diffuse arrangement of immunoreactive processes invades all zones of the mushroom body calyces in Periplaneta. These processes derive from an ascending axon ascribed to a dorsal unpaired median neuron at the maxillary segment of the subesophageal ganglion. In both taxa octopamine-immunoreactive processes invade only the γ lobes of the mushroom bodies, omitting their other divisions. The present observations are discussed with respect to possible roles of octopamine in sensory integration and association. © 2005 Wiley-Liss, Inc.
• Sjöholm, M., Sinakevitch, I., Ignell, R., Strausfeld, N. J., & Hansson, B. S. (2005). Organization of Kenyon cells in subdivisions of the mushroom bodies of a lepidopteran insect. Journal of Comparative Neurology, 491(3), 290-304.
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  PMID: 16134139;Abstract: The mushroom bodies are paired structures in the insect brain involved in complex functions such as memory formation, sensory integration, and context recognition. In many insects these centers are elaborate, sometimes comprising several hundred thousand neurons. The present account describes the mushroom bodies of Spodoptera littoralis, a moth extensively used for studies of olfactory processing and conditioning. The mushroom bodies of Spodoptera consist of only about 4,000 large-diameter Kenyon cells. However, these neurons are recognizably similar to morphological classes of Kenyon cells identified in honey bees, Drosophila, and cockroaches. The spodopteran mushroom body is equipped with three major divisions of its vertical and medial lobe, one of which, the gamma lobe, is supplied by clawed class II Kenyon cells as in other described taxa. Of special interest is the presence of a discrete tract (the Y tract) of axons leading from the calyx, separate from the pedunculus, that innervates lobelets above and beneath the medial lobe, close to the latter's origin from the pedunculus. This tract is comparable to tracts and resultant lobelets identified in cockroaches and termites. The article discusses possible functional roles of the spodopteran mushroom body against the background of olfactory behaviors described from this taxon and discusses the possible functional relevance of mushroom body structure, emphasizing similarities and dissimilarities with mushroom bodies of other species, in particular the fruit fly, Drosophila melanogaster. © 2005 Wiley-Liss, Inc.
• Strausfeld, N. J. (2005). The evolution of crustacean and insect optic lobes and the origins of chiasmata. Arthropod Structure and Development, 34(3), 235-256.
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  Abstract: In malacostracan crustaceans and insects three nested optic lobe neuropils are linked by two successive chiasmata that reverse and then reverse again horizontal rows of retinotopic columns. Entomostracan crustaceans possess but two retinotopic neuropils connected by uncrossed axons: a distal lamina and an inner plate-like neuropil, here termed the visual tectum that is contiguous with the protocerebrum. This account proposes an evolutionary trajectory that explains the origin of chiasmata from an ancestral taxon lacking chiasmata. A central argument employed is that the two optic lobe neuropils of entomostracans are homologous to the lamina and lobula plate of insects and malacostracans, all of which contain circuits for motion detection - an archaic attribute of visual systems. An ancestral duplication of a cell lineage originally providing the entomostracan lamina is proposed to have given rise to an outer and inner plexiform layer. It is suggested that a single evolutionary step resulted in the separation of these layers and, as a consequence, their developmental connection by a chiasma with the inner layer, the malacostracan-insect medulla, still retaining its uncrossed connections to the deep plate-like neuropil. It is postulated that duplication of cell lineages of the inner proliferation zone gave rise to a novel neuropil, the lobula. An explanation for the second chiasma is that it derives from uncrossed axons originally supplying the visual tectum that subsequently supply collaterals to the opposing surface of the newly evolved lobula. A cladistic analysis based on optic lobe anatomy of taxa possessing compound eyes supports a common ancestor of the entomostracans, malacostracan crustaceans, and insects. © 2005 Elsevier Ltd. All rights reserved.
• Sztarker, J., Strausfeld, N. J., & Tomsic, D. (2005). Organization of optic lobes that support motion detection in a semiterrestrial crab. Journal of Comparative Neurology, 493(3), 396-411.
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  PMID: 16261533;PMCID: PMC2638986;Abstract: There is a mismatch between the documentation of the visually guided behaviors and visual physiology of decapods (Malacostraca, Crustacea) and knowledge about the neural architecture of their visual systems. The present study provides a description of the neuroanatomical features of the four visual neuropils of the grapsid crab Chasmagnathus granulatus, which is currently used as a model for investigating the neurobiology of learning and memory. Visual memory in Chasmagnathus is thought to be driven from within deep retinotopic neuropil by large-field motion-sensitive neurons. Here we describe the neural architecture characterizing the Chasmagnathus lobula, in which such neurons are found. It is shown that, unlike the equivalent region of insects, the malacostracan lobula is densely packed with columns, the spacing of which is the same as that of retinotopic units of the lamina. The lobula comprises many levels of strata and columnar afferents that supply systems of tangential neurons. Two of these, which are known to respond to movement across the retina, have orthogonally arranged dendritic fields deep in the lobula. They also show evidence of dye coupling. We discuss the significance of commonalties across taxa with respect to the organization of the lamina and medulla and contrasts these with possible taxon-specific arrangements of deeper neuropils that support systems of matched filters. © 2005 Wiley-Liss, Inc.
• Farris, S. M., Abrams, A. I., & Strausfeld, N. J. (2004). Development and morphology of Class II Kenyon cells in the mushroom bodies of the honey bee, Apis mellifera. Journal of Comparative Neurology, 474(3), 325-339.
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  PMID: 15174077;Abstract: Class II Kenyon cells, defined by their early birthdate and unique dendritic arborizations, have been observed in the mushroom bodies of evolutionarily divergent insects. In the fruit fly Drosophila melanogaster, Class II (also called clawed) Kenyon cells are well known for their extensive reorganization that occurs during metamorphosis. The present account reports for the first time the occurrence of mushroom body reorganization during metamorphosis in holometabolous insect species outside of the Diptera. In the honey bee, Apis mellifera, Class II Kenyon cells show signs of degeneration and undergo a subtle reshaping of their axons during metamorphosis. Unlike in Drosophila, reorganization of Class II Kenyon cells in the honey bee does not involve the loss of axon branches. In contrast, the mushroom bodies of closely related hymenopteran species, the polistine wasps, undergo a much more dramatic restructuring near the end of metamorphosis. Immunohistochemistry, dextran fills, and Golgi impregnations illuminate the heterogeneous nature of Class II Kenyon cells in the developing and adult honey bee brain, with subpopulations differing in the location of dendritic arbors within the calyx, and branching pattern in the lobes. Furthermore, polyclonal antibodies against the catalytic subunit of Drosophila protein kinase A (anti-DC0) label an unusual and previously undescribed trajectory for these neurons. The observed variations in morphology indicate that subpopulations of Class II Kenyon cells in the honey bee can likely be further defined by significant differences in their specific connections and functions within the mushroom bodies. © 2004 Wiley-Liss, Inc.
• Higgins, C. M., Douglass, J. K., & Strausfeld, N. J. (2004). The computational basis of an identified neuronal circuit for elementary motion detection in dipterous insects. Visual Neuroscience, 21(4), 567-586.
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  PMID: 15579222;Abstract: Based on comparative anatomical studies and electrophysiological experiments, we have identified a conserved subset of neurons in the lamina, medulla, and lobula of dipterous insects that are involved in retinotopic visual motion direction selectivity. Working from the photoreceptors inward, this neuronal subset includes lamina amacrine (α) cells, lamina monopolar (L2) cells, the basket T-cell (T1 or β), the transmedullary cell Tm1, and the T5 bushy T-cell. Two GABA-immunoreactive neurons, the transmedullary cell Tm9 and a local interneuron at the level of T5 dendrites, are also implicated in the motion computation. We suggest that these neurons comprise the small-field elementary motion detector circuits the outputs of which are integrated by wide-field lobula plate tangential cells. We show that a computational model based on the available data about these neurons is consistent with existing models of biological elementary motion detection, and present a comparable version of the Hassenstein-Reichardt (HR) correlation model. Further, by using the model to synthesize a generic tangential cell, we show that it can account for the responses of lobula plate tangential cells to a wide range of transient stimuli, including responses which cannot be predicted using the HR model. This computational model of elementary motion detection is the first which derives specifically from the functional organization of a subset of retinotopic neurons supplying the lobula plate. A key prediction of this model is that elementary motion detector circuits respond quite differently to small-field transient stimulation than do spatially integrated motion processing neurons as observed in the lobula plate. In addition, this model suggests that the retinotopic motion information provided to wide-field motion-sensitive cells in the lobula is derived from a less refined stage of processing than motion inputs to the lobula plate.
• Kwon, H., Lent, D. D., & Strausfeld, N. J. (2004). Spatial learning in the restrained American cockroach Periplaneta americana. Journal of Experimental Biology, 207(2), 377-383.
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  PMID: 14668321;Abstract: Spatial learning abilities were tested in restrained cockroaches by observing antennal projection responses towards the positions of a learned visual cue perceived monocularly by one eye in the context of a second stimulus provided to the contralateral eye. Memory of the position of the conditioning stimulus relative to the contralateral reference stimulus was tested by altering the relative positions of the two stimuli. Memory of the conditioning stimulus is retained if the angle between the conditioning stimulus and the contralateral reference stimulus is maintained. The results suggest that during learning the insect recognizes spatial relationships between the conditioning stimulus and the contralateral reference stimulus. Possible mechanisms, such as retinotopic matching versus angular matching, are discussed.
• Sinakevitch, I., & Strausfeld, N. J. (2004). Chemical Neuroanatomy of the Fly's Movement Detection Pathway. Journal of Comparative Neurology, 468(1), 6-23.
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  PMID: 14648688;Abstract: In Diptera, subsets of small retinotopic neurons provide a discrete channel from achromatic photoreceptors to large motion-sensitive neurons in the lobula complex. This pathway is distinguished by specific affinities of its neurons to antisera raised against glutamate, aspartate, γ-aminobutyric acid (GABA), choline acetyltransferase (ChAT), and a N-methyl-D-aspartate type 1 receptor protein (NMDAR1). Large type 2 monopolar cells (L2) and type 1 amacrine cells, which in the external plexiform layer are postsynaptic to the achromatic photoreceptors R1-R6, express glutamate immunoreactivity as do directionally selective motion-sensitive tangential neurons of the lobula plate. L2 monopolar cells ending in the medulla are accompanied by terminals of a second efferent neuron T1, the dendrites of which match NMDAR1-immunoreactive profiles in the lamina. L2 and T1 endings visit ChAT and GABA-immunoreactive relays (transmedullary neurons) that terminate from the medulla in a special layer of the lobula containing the dendrites of directionally selective retinotopic T5 cells. T5 cells supply directionally selective wide-field neurons in the lobula plate. The present results suggest a circuit in which initial motion detection relies on interactions among amacrines and T1, and the subsequent convergence of T1 and L2 at transmedullary cell dendrites. Convergence of ChAT-immunoreactive and GABA-immunoreactive transmedullary neurons at T5 dendrites in the lobula, and the presence there of local GABA-immunoreactive interneurons, are suggested to provide excitatory and inhibitory elements for the computation of motion direction. A comparable immunocytological organization of aspartate- and glutamate-immunoreactive neurons in honeybees and cockroaches further suggests that neural arrangements providing directional motion vision in flies may have early evolutionary origins. © 2003 Wiley-Liss, Inc.
• Strausfeld, N., Larsson, M. C., Hansson, B. S., & Strausfeld, N. J. (2004). A simple mushroom body in an African scarabid beetle. The Journal of comparative neurology, 478(3).
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  This account describes novel mushroom body organization in a coleopteran insect, the African fruit chafer Pachnoda marginata. Each of its prominent mushroom bodies possesses a pair of simple calyces comprising two populations of Kenyon cells, the dendrites of which are organized into a central and an annular zone. Kenyon cells of the central zone extend their dendrites downward and toward the perimeter of the calyx. Their axon-like processes in the pedunculus are densely packed to make up a distinctive shaft of neuropil. Toward the front of the brain, the shafts, one from each calyx, bifurcate to provide a pair of subdivisions in the medial and vertical lobes. Dendrites of Kenyon cells supplying the annular zone extend from the calyx perimeter toward its center. Axons from the annular zones of both calyces together provide a sleeve of axons that ensheaths the two shafts. Sleeve axons bifurcate to provide a second pair of divisions in each of the lobes. These arrangements provide each lobe with a discrete representation of the two Kenyon cell populations of the two calyces. Kenyon cells supplying the central zone have dendritic morphologies reminiscent of class II clawed Kenyon cells that supply the gamma lobes in other taxa. Kenyon cells supplying axons to the sleeve are suggestive of class III Kenyon cell morphologies described from cockroaches and termites. Elaborate intrinsic neurons, comparable to exotic intrinsic neurons in the honey bee gamma lobes, have processes that interact with shaft axons. The present observations suggest that mushroom bodies of Pachnoda represent either a basal organization entirely lacking class I Kenyon cells or an evolutionary modification in which there is no clear morphological distinction of class I and II Kenyon cells. In either case, cellular organization in Pachnoda's mushroom body is simple compared with that of other taxa.
• Douglass, J. K., & Strausfeld, N. J. (2003). Retinotopic pathways providing motion-selective information to the lobula from peripheral elementary motion-detecting circuits. Journal of Comparative Neurology, 457(4), 326-344.
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  PMID: 12561074;Abstract: Recordings from afferent channels from the medulla supplying deep neuropils of the fly's optic lobes reveal different filter properties among the three classes of afferent neurons: transmedullary cells, T2 neurons, and Y cells. Whereas transmedullary cells respond to local flicker stimuli without discriminating these from directional or oriented motion, the T2 afferent neurons show clear motion orientation selectivity, which corresponds closely with a morphological bias in the orientation of their dendrites and could also be influenced by systems of local recurrent neurons in the medulla. A Y cell having a clearly defined terminal in the lobula, but having dendrite-like processes in the medulla and, possibly, the lobula plate, discriminates the direction of motion and its orientation. These results demonstrate unambiguously that the lobula receives information about motion and that the channels carrying it are distinct from those supplying wide-field motion-selective neurons in the lobula plate. Furthermore, recordings from a newly identified recurrent neuron linking the lobula back to the inner medulla demonstrate that the lobula discriminates nondirectional edge motion from flicker, thereby reflecting a property of this neuropil that is comparable with that of primary visual cortex in cats. The present findings support the proposal that elementary motion detecting circuits supply several parallel channels through the medulla, which segregate to, but are not shared by, the lobula and the lobula plate. The results are discussed in the context of other intracellular recordings from retinotopic neurons and with analogous findings from mammalian visual systems. © 2003 Wiley-Liss, Inc.
• Sinakevitch, I., Douglass, J. K., Scholtz, G., Loesel, R., & Strausfeld, N. J. (2003). Conserved and Convergent Organization in the Optic Lobes of Insects and Isopods, with Reference to Other Crustacean Taxa. Journal of Comparative Neurology, 467(2), 150-172.
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  PMID: 14595766;Abstract: The shared organization of three optic lobe neuropils-the lamina, medulla, and lobula-linked by chiasmata has been used to support arguments that insects and malacostracans are sister groups. However, in certain insects, the lobula is accompanied by a tectum-like fourth neuropil, the lobula plate, characterized by wide-field tangential neurons and linked to the medulla by uncrossed axons. The identification of a lobula plate in an isopod crustacean raises the question of whether the lobula plate of insects and isopods evolved convergently or are derived from a common ancestor. This question is here investigated by comparisons of insect and crustacean optic lobes. The basal branchiopod crustacean Triops has only two visual neuropils and no optic chiasma. This finding contrasts with the phyllocarid Nebalia pugettensis, a basal malacostracan whose lamina is linked by a chiasma to a medulla that is linked by a second chiasma to a retinotopic outswelling of the lateral protocerebrum, called the protolobula. In Nebalia, uncrossed axons from the medulla supply a minute fourth optic neuropil. Eumalacostracan crustaceans also possess two deep neuropils, one receiving crossed axons, the other uncrossed axons. However, in primitive insects, there is no separate fourth optic neuropil. Malacostracans and insects also differ in that the insect medulla comprises two nested neuropils separated by a layer of axons, called the Cuccati bundle. Comparisons suggest that neuroarchitectures of the lamina and medulla distal to the Cuccati bundle are equivalent to the eumalacostracan lamina and entire medulla. The occurrence of a second optic chiasma and protolobula are suggested to be synapomorphic for a malacostracan/insect clade. © 2003 Wiley-Liss, Inc.
• Steinbrecht, A., & Strausfeld, N. (2003). A comment from the editors. Arthropod Structure and Development, 32(1), 1-.
• Strausfeld, N. J., Sinakevitch, I., & Vilinsky, I. (2003). The mushroom bodies of Drosophila melanogaster: An immunocytological and golgi study of Kenyon cell organization in the calyces and lobes. Microscopy Research and Technique, 62(2), 151-169.
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  PMID: 12966500;Abstract: Golgi impregnations reveal a variety of dendritic morphologies amongst Kenyon cells in the mushroom bodies of Drosophila melanogaster. Different morphological types of Kenyon cells contribute axon-like processes to five divisions of the medial and vertical lobes. Four of these divisions have characteristic affinities to antibodies raised against aspartate, glutamate, and taurine. A newly described posterior subdivision of the medial lobe, here named the βc lobe with its vertical branch αc, comprises glutamatergic Kenyon cells that are probably homologous to glutamatergic Kenyon cells in the cockroach and honey bee, and are the last neurons to differentiate. The first neurons to differentiate, which supply the γ lobe, are equipped with clawed dendritic specializations and are the structural homologues of clawed class II Kenyon cells supplying the γ lobes in cockroaches and honey bees. Three intermediate divisions lie between the βc lobe and γ lobe. These are, from the back towards the front, the β lobe, the β′ lobe, and a narrow division between β′ and γ called the β″ lobe. The fused calyx of the Drosophila mushroom body is comparable to the double calyces of Hymenoptera, here exemplified by a basal taxon, Diprion pini. Further similarities between the hymenopteran calyces and those of Drosophila are suggested by the segregation of different types of Kenyon cell dendrites within the calyx neuropil. The organization of afferents from the antennal lobes also defines regions in the Drosophila calyx that may be homologous to the lip and basal ring regions of the honey bee calyces. As in honey bees, GABAergic processes densely invade Drosophila's calyces, which also contain a sparse but uniform distribution of octopaminergic elements. © 2003 Wiley-Liss, Inc.
• Strausfeld, N., Douglass, J. K., & Strausfeld, N. J. (2003). Anatomical organization of retinotopic motion-sensitive pathways in the optic lobes of flies. Microscopy research and technique, 62(2).
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  Anatomical methods have identified conserved neuronal morphologies and synaptic relationships among small-field retinotopic neurons in insect optic lobes. These conserved cell shapes occur across many species of dipteran insects and are also shared by Lepidoptera and Hymenoptera. The suggestion that such conserved neurons should participate in motion computing circuits finds support from intracellular recordings as well as older studies that used radioactive deoxyglucose labeling to reveal strata with motion-specific activity in an achromatic neuropil called the lobula plate. While intracellular recordings provide detailed information about the motion-sensitive or motion-selective responses of identified neurons, a full understanding of how arrangements of identified neurons compute and integrate information about visual motion will come from a multidisciplinary approach that includes morphological circuit analysis, the use of genetic mutants that exhibit specific deficits in motion processing, and biomimetic models. The latter must be based on the organization and connections of real neurons, yet provide output properties similar to those of more traditional theoretical models based on behavioral observations that date from the 1950s. Microsc. Res. Tech. 62:132-150, 2003.
• Strausfeld, N., Farris, S. M., & Strausfeld, N. J. (2003). A unique mushroom body substructure common to basal cockroaches and to termites. The Journal of comparative neurology, 456(4).
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  The mushroom bodies of the cockroach Periplaneta americana are made up of intrinsic neurons (class I and class II Kenyon cells) with dendrites in a dorsal calyx and axons that bifurcate into medial and vertical lobes. Here, we describe a substructure of the cockroach mushroom bodies composed of a previously unrecognized class of Kenyon cells with distinct morphologies. The embryonically produced class III Kenyon cells form a separate accessory calyx below the calyx proper. The medial branches of class III Kenyon cell axons form the previously described "gamma bulb," whereas the vertical branches leave the vertical lobe to form a toroidal "lobelet" around the posterior surface. Taking advantage of the morphologically and immunochemically distinct nature of the lobelet, we have attempted to determine the distribution of this unique structure in other insects of the taxon Dictyoptera (cockroaches, mantises, and termites). Our data indicate that the lobelet is present only in basal cockroaches and in termites, supporting existing theories of a close phylogenetic relationship between these groups. Higher termites possess a duplicated lobe structure due to immense elaboration of the processes of class III Kenyon cells. The degree of complexity in the mushroom body lobes of termites agrees with current taxonomic arrangements of the Isoptera based on non-neural morphological and DNA sequence analyses. It thus appears that the evolution of the Dictyoptera has been accompanied by increasing complexity of the mushroom bodies, achieved in part through the further specialization and elaboration of a subset of Kenyon cells.
• Loesel, R., Nässel, D. R., & Strausfeld, N. J. (2002). Common design in a unique midline neuropil in the brains of arthropods. Arthropod Structure and Development, 31(1), 77-91.
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  PMID: 18088972;Abstract: Most insects possess an assemblage of midline neuropils in their protocerebrum called the central complex. Recent studies have identified comparable assemblages in the malacostracan protocerebrum. Studies of Drosophila melanogaster locomotory mutants suggest that in insects one role for the central complex might be to orchestrate limb actions. This is anecdotally supported by comparisons amongst insects suggesting that elaboration of central complex architecture correlates with complexity of limb motor repertoires. The present account describes immunocytochemical and neuroanatomical observations that reveal common design principles amongst midline neuropils in four arthropod clades, the hexapods, crustaceans, chilopods, and chelicerates and the absence of midline neuropils in diplopods. The chilopod midline neuropil, which is columnar and stratified and lacks chiasmal axons to the dorsal protocerebrum or connections to discrete satellite regions, may represent the plesiomorphous condition. The complete absence of a midline neuropil in diplopods supports previous neuroanatomical studies suggesting that the 'Myriapoda' are an artificial paraphyletic group. The columnar and layered arcuate midline neuropils of chelicerates are compared with columnar and layered midline neuropils of chilopods. No midline neuropil has been identified in a lophotrochozoan outgroup, the Polychaeta. ©2002 Elsevier Science Ltd. All rights reserved.
• Strausfeld, N. J. (2002). Organization of the honey bee mushroom body: Representation of the calyx within the vertical and gamma lobes. Journal of Comparative Neurology, 450(1), 4-33.
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  PMID: 12124764;Abstract: Studies of the mushroom bodies of Drosophila melanogaster have suggested that their gamma lobes specifically support short-term memory, whereas their vertical lobes are essential for long-term memory. Developmental studies have demonstrated that the Drosophila gamma lobe, like its equivalent in the cockroach Periplaneta americana, is supplied by a special class of intrinsic neuron - the clawed Kenyon cells - that are the first to differentiate during early development. To date, however, no account identifies a corresponding lobe in the honey bee, another taxon used extensively for learning and memory research. Received opinion is that, in this taxon, each of the mushroom body lobes comprises three parallel divisions representing one of three concentric zones of the calyces, called the lip, collar, and basal ring. The present account shows that, although these zones are represented in the lobes, they occupy only two thirds of the vertical lobe. Its lowermost third receives the axons of the clawed class II Kenyon cells, which are the first to differentiate during early development and which represent the whole calyx. This component of the lobe is anatomically and developmentally equivalent to the gamma lobe of Drosophila and has been here named the gamma lobe of the honey bee. A new class of intrinsic neurons, originating from perikarya distant from the mushroom body, provides a second system of parallel fibers from the calyx to the gamma lobe. A region immediately beneath the calyces, called the neck, is invaded by these neurons as well as by a third class of intrinsic cell that provides connections within the neck of the pedunculus and the basal ring of the calyces. In the honey bee, the gamma lobe is extensively supplied by afferents from the protocerebrum and gives rise to a distinctive class of efferent neurons. The terminals of these efferents target protocerebral neuropils that are distinct from those receiving efferents from divisions of the vertical lobe that represent the lip, collar, and basal ring. The identification of a gamma lobe unites the mushroom bodies of evolutionarily divergent taxa. The present findings suggest the need for critical reinterpretation of studies that have been predicated on early descriptions of the mushroom body's lobes. © 2002 Wiley-Liss, Inc.
• Campbell, H. R., & Strausfeld, N. J. (2001). Learned discrimination of pattern orientation in walking flies. Journal of Experimental Biology, 204(1), 1-14.
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  PMID: 11104706;Abstract: To determine the pattern-orientation discrimination ability of blowflies, Phaenicia sericata, a learning/memory assay was developed in which sucrose served as the reward stimulus and was paired with one of two visual gratings of different orientations. Individual, freely walking flies with clipped wings were trained to discriminate between pairs of visual patterns presented in the vertical plane. During training trials, individual flies learned to search preferentially at the rewarded stimulus. In subsequent testing trials, flies continued to exhibit a learned preference for the previously rewarded stimulus, demonstrating an ability to discriminate between the two visual cues. Flies learned to discriminate between horizontal and vertical gratings, +45° (relative to a 0° vertical) and -45° gratings, and vertical and +5° gratings. Individual patterns of learning and locomotive behavior were observed in the pattern of exploration during training trials. The features of the visual Cue critical for discrimination of orientation are discussed.
• Farris, S. M., & Strausfeld, N. J. (2001). Development of laminar organization in the mushroom bodies of the cockroach: Kenyon cell proliferation, outgrowth, and maturation. Journal of Comparative Neurology, 439(3), 331-351.
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  PMID: 11596058;Abstract: The mushroom bodies of the insect brain are lobed integration centers made up of tens of thousands of parallel-projecting axons of intrinsic (Kenyon) cells. Most of the axons in the medial and vertical lobes of adult cockroach mushroom bodies derive from class I Kenyon cells and are organized into regular, alternating pairs (doublets) of pale and dark laminae. Organization of Kenyon cell axons into the adult pattern of laminae occurs gradually over the course of nymphal development. Newly hatched nymphs possess tiny mushroom bodies with lobes containing a posterior lamina of ingrowing axons, followed by a single doublet, which is flanked anteriorly by a γ layer composed of class II Kenyon cells. Golgi impregnations show that throughout nymphal development, regardless of the number of doublets present, the most posterior lamina serves as the "ingrowth lamina" for axons of newborn Kenyon cells. Axons of the ingrowth lamina are taurine- and synaptotagmin-immunonegative. They produce fine growth cone tipped filaments and long perpendicularly oriented collaterals along their length. The maturation of these Kenyon cells and the formation of a new lamina are marked by the loss of filaments and collaterals, as well as the onset of taurine and synaptotagmin expression. Class I Kenyon cells thus show plasticity in both morphology and transmitter expression during development. In a hemimetabolous insect such as the cockroach, juvenile stages are morphologically and behaviorally similar to the adult. The mushroom bodies of these insects must be functional from hatching onward, while thousands of new neurons are added to the existing structure. The observed developmental plasticity may serve as a mechanism by which extensive postembryonic development of the mushroom bodies can occur without disrupting function. This contrasts with the more evolutionarily derived holometabolous insects, such as the honey bee and the fruit fly, in which nervous system development is accomplished in a behaviorally simple larval stage and a quiescent pupal stage. © 2001 Wiley-Liss, Inc.
• Jabłoński, P., & Strausfeld, N. J. (2001). Exploitation of an ancient escape circuit by an avian predator: Relationships between taxon-specific prey escape circuits and the sensitivity to visual cues from the predator. Brain, Behavior and Evolution, 58(4), 218-240.
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  PMID: 11964498;Abstract: The painted redstart Myioborus pictus uses visual displays to flush, pursue, and then capture an abundance of brachyceran Diptera that are equipped with giant fiber escape circuits. This paper investigates the relationships between features of the giant fiber system, the structure of visual stimuli produced by redstarts and their effectiveness in eliciting escape reactions by flies. The results show that dipterous taxa having large-diameter giant fibers extending short distances from the brain to motor neurons involved in escape are flushed at greater distances than taxa with longer and small-diameter giant fibers. The results of behavioral tests show the importance of angular acceleration of expanding image edges on the compound eye in eliciting escape responses. Lateral motion of stimulus profile edges as well as structured visual profiles additionally contribute to the sensitivity of one or more neural systems that trigger escape. Retinal subtense and angular velocity are known to trigger physiological responses in fly giant fiber circuits, but the contributions of edge length and lateral motion in a looming stimulus suggest that escape pathways might also receive inputs from circuits that are tuned to different types of motion. The present results suggest that these several properties of escape pathways have contributed to the evolution of foraging displays and plumage patterns in flush-pursuing birds. Copyright © 2002 S. Karger AG, Basel.
• Sinakevitch, I., Farris, S. M., & Strausfeld, N. J. (2001). Taurine-, aspartate- and glutamate-like immunoreactivity identifies chemically distinct subdivisions of Kenyon cells in the cockroach mushroom body. Journal of Comparative Neurology, 439(3), 352-367.
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  PMID: 11596059;Abstract: The lobes of the mushroom bodies of the cockroach Periplaneta americana consist of longitudinal modules called laminae. These comprise repeating arrangements of Kenyon cell axons, which like their dendrites and perikarya have an affinity to one of three antisera: to taurine, aspartate, or glutamate. Taurine-immunopositive laminae alternate with immunonegative ones. Aspartate-immunopositive Kenyon cell axons are distributed across the lobes. However, smaller leaf-like ensembles of axons that reveal particularly high affinities to anti-aspartate are embedded within taurine-positive laminae and occur in the immunonegative laminae between them. Together, these arrangements reveal a complex architecture of repeating subunits whose different levels of immunoreactivity correspond to broader immunoreactive layers identified by sera against the neuromodulator FMRFamide. Throughout development and in the adult, the most posterior lamina is glutamate immunopositive. Its axons arise from the most recently born Kenyon cells that in the adult retain their juvenile character, sending a dense system of collaterals to the front of the lobes. Glutamate-positive processes intersect aspartate- and taurine-immunopositive laminae and are disposed such that they might play important roles in synaptogenesis or synapse modification. Glutamate immunoreactivity is not seen in older, mature axons, indicating that Kenyon cells show plasticity of neurotransmitter phenotype during development. Aspartate may be a universal transmitter substance throughout the lobes. High levels of taurine immunoreactivity occur in broad laminae containing the high concentrations of synaptic vesicles. © 2001 Wiley-Liss, Inc.
• Douglass, J. K., & Strausfeld, N. J. (2000). Optic flow representation in the optic lobes of Diptera: Modeling innervation matrices onto collators and their evolutionary implications. Journal of Comparative Physiology - A Sensory, Neural, and Behavioral Physiology, 186(9), 799-811.
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  PMID: 11085634;Abstract: A network model of optic flow processing, based on physiological and anatomical features of motion-processing neurons, is used to investigate the role of small-field motion detectors emulating T5 cells in producing optic flow selective properties in wide-field collator neurons. The imposition of different connectivities can mimic variations observed in comparative studies of lobula plate architecture across the Diptera. The results identify two features that are crucial for optic flow selectivity: the broadness of the spatial patterns of synaptic connections from motion detectors to collators, and the relative contributions of excitatory and inhibitory synaptic outputs. If these two aspects of the innervation matrix are balanced appropriately, the network's sensitivity to perturbations in physiological properties of the small-field motion detectors is dramatically reduced, suggesting that sensory systems can evolve robust mechanisms that do not rely upon precise control of network parameters. These results also suggest that alternative lobula plate architectures observed in insects are consistent in allowing optic flow selective properties in wide-field neurons. The implications for the evolution of optic flow selective neurons are discussed.
• Douglass, J. K., & Strausfeld, N. J. (2000). Optic flow representation in the optic lobes of Diptera: Modeling the role of T5 directional tuning properties. Journal of Comparative Physiology - A Sensory, Neural, and Behavioral Physiology, 186(9), 783-797.
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  PMID: 11085633;Abstract: An evolutionarily conserved system of small retinotopic neurons in dipteran insects, called bushy T-cells, provides information about directional motion to large collator neurons in the lobula plate. Physiological and anatomical features of these cells provide the basis for a model that is used to investigate requirements for generating optic flow selectivity in collators while allowing for evolutionary variations. This account focuses on the role of physiological tuning properties of T5 neurons. Various flow fields are defined as inputs to retinotopic arrays of T5 cells, the responses of which are mapped onto collators using innervation matrices that promote selectivity for flow type and position. Properties known or inferred from physiological and anatomical studies of neurons contributing to motion detection are incorporated into the model: broad tuning to local motion direction and the representation of each visual sampling unit by a quartet of small-field T5-like neurons with orthogonal preferred directions. The model predicts hitherto untested response properties of optic flow selective collators, and predicts that selectivity for a given flow field can be highly sensitive to perturbations in physiological properties of the motion detectors.
• Jabłoński, P., & Strausfeld, N. J. (2000). Exploitation of an ancient escape circuit by an avian predator: Prey sensitivity to model predator display in the field. Brain, Behavior and Evolution, 56(2), 94-106.
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  PMID: 11111136;Abstract: Certain insectivorous birds, such as the painted redstart (Myioborus pictus), undertake flush pursuit - a characteristic display that elicits an escape reaction by an insect, which the bird then chases in the air and eats. This account describes experiments showing that flush pursuit uses visual displays, which are likely to exploit an ancient neural circuit in dipteran insects, the visual systems of which are well documented as detecting looming stimuli and triggering an escape responses. Using models that decompose components of the redstart display, specific elements of the display were analyzed for their contribution in triggering visually induced escape behavior by dipterous insects. Elements tested were pivoting body movements, patterning on the spread tail and wings, and visual contrast of model redstarts against pale and dark backgrounds. We show that contrasting patterns within the plumage are crucial to foraging success, as is contrast of the bird against a background. Visual motion also significantly contributes to the successful flushing. In contrast, unpatterned models and patterned models that do not contrast with the background are less successful in eliciting escape responses of flies. Natural visual stimuli provided by Myioborus pictus are similar to those known to trigger looming and time-to-collision neurons in the escape circuits of flies and other insects, such as orthopterans. We propose that the tuning properties of these neural pathways might have contributed to the evolution of foraging displays in flush-pursuing birds. Copyright (C) 2000 S. Karger AG, Basel.
• Steinbrecht, A., & Strausfeld, N. (2000). Editorial. Arthropod Structure and Development, 29(1), 1-.
• Strausfeld, N. J., Homberg, U., & Kloppenburg, P. (2000). Erratum: Parallel organization in honey bee mushroom bodies by peptidergic kenyon cells (Journal of Comparative Neurology 424 (179-195)). Journal of Comparative Neurology, 428(4), 760-.
• Strausfeld, N. J., Homburg, U., & Kloppenberg, P. (2000). Parallel organization in honey bee mushroom bodies by peptidergic Kenyon cells. Journal of Comparative Neurology, 424(1), 179-195.
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  PMID: 10888747;Abstract: Antisera against the neuromodulatory peptides, Phe-Met-Arg-Phe-NH2- amide (FMRF-amide) and gastrin cholecystokinin, demonstrate that the mushroom bodies of honey bees are subdivided longitudinally into strata. Three- dimensional reconstructions demonstrate that these strata project in parallel through the entire pedunculus and through the medial and vertical lobes. Immunostaining reveals clusters of immunoreactive cell bodies within the calyx cups and immunoreactive bundles of axons that line the inside of the calyx cup and lead to strata. Together, these features reveal that immunoreactive strata are composed of Kenyon cell axons rather than extrinsic elements, as suggested previously by some authors. Sorting amongst Kenyon cell axons into their appropriate strata already begins in the calyx before these axons enter the pedunculus. The three main concentric divisions of each calyx (the lip, collar, and basal ring) are divided further into immunoreactive and immunonegative zones. The lip neuropil is divided into two discrete zones, the collar neuropil is divided into five zones, and the basal ring neuropil is divided into four zones. Earlier studies proposed that the lip, collar, and basal ring are represented by three broad bands in the lobes: axons from adjacent Kenyon cell dendrites in the calyces are adjacent in the lobes even after their polar arrangements in the calyces have been transformed to rectilinear arrangements in the lobes. The universality of this arrangement is not supported by the present results. Although immunoreactive zones are found in all three calycal regions, immunoreactive strata in the lobes occur mainly in the two bands that were ascribed previously to the collar and the basal ring. In the lobes, immunoreactive strata are visited by the dendrites of efferent neurons that carry information from the mushroom bodies to other parts of the brain. Morphologically and chemically distinct subdivisions through the pedunculus and lobes of honey bees are comparable to longitudinal subdivisions demonstrated in the mushroom bodies of other insects, such as the cockroach Periplaneta americana. The functional and evolutionary significance of the results is discussed. (C) 2000 Wiley-Liss, Inc.
• Wicklein, M., & Strausfeld, N. J. (2000). Organization and significance of neurons that detect change of visual depth in the hawk moth Manduca sexta. Journal of Comparative Neurology, 424(2), 356-376.
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  PMID: 10906708;Abstract: Visual stimuli representing looming or receding objects can be decomposed into four parameters: change in luminance; increase or decrease of area; increase or decrease of object perimeter length; and motion of the object's perimeter or edge. This paper describes intracellular recordings from visual neurons in the optic lobes of Manduca sexta that are selectively activated by certain of these parameters. Two classes of wide-field neurons have been identified that respond selectively to looming and receding stimuli. Class 1 cells respond to parameters of the image other than motion stimuli. They discriminate an approaching or receding disc from an outwardly or inwardly rotating spiral, being activated only by the disc and not by the spiral. Class 2 neurons respond to moving edges. They respond both to movement of the spiral and to an approaching or receding disc. These two classes are further subdivided into neurons that are excited by image expansion (looming) and are inhibited by image contraction (antilooming). Class 2 neurons also respond to horizontal and vertical movement of gratings over the retina. Stimulating class 1 and 2 neurons with white discs against a dark background results in the same activation as stimulation with dark discs against a white background, demonstrating that changes in luminance play no role in the detection of looming or antilooming. The present results show that the two types of looming-sensitive neurons in M. sexta use different mechanisms to detect the approach or retreat of an object. It is proposed that cardinal parameters for this are change of perimeter length detected by class 1 neurons and expansion or contraction visual flow fields detected by class 2 neurons. These two classes also differ with respect to their polarity, the former comprising centripetal cells from the optic lobes to the midbrain, the latter comprising centrifugal neurons from the midbrain to the optic lobes. The significance of these arrangements with respect to hovering flight is discussed. (C) 2000 Wiley-Liss, Inc.
• Strausfeld, N. J. (1999). A brain region in insects that supervises walking. Progress in Brain Research, 123, 273-284.
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  PMID: 10635723;
• Strausfeld, N. J., & Yongsheng, L. i. (1999). Organization of olfactory and multimodal afferent neurons supplying the calyx and pedunculus of the cockroach mushroom bodies. Journal of Comparative Neurology, 409(4), 603-625.
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  PMID: 10376743;Abstract: The mushroom bodies of neopteran insects are considered to be higher olfactory centers because their calyces receive abundant collaterals of projection neurons from the antennal lobes. However, intracellular recordings of mushroom body efferent neurons demonstrate that they respond to multimodal stimuli, implying that the mushroom bodies receive a variety of sensory cues. The present account describes new features of the organization of afferent neurons supplying the calyces of the cockroach Periplaneta americana. Afferent terminals segment the calyces into discrete zones, I, II, III, and IIIA, which receive afferents from 1) two discrete populations of sexually isomorphic olfactory glomeruli, 2) two types of male-specific olfactory glomeruli, 3) the optic lobes, and 4) multimodal interneurons that originate in protocerebral neuropils. In addition, intracellular recordings and dye fills show that at least four morphologically distinct GABAergic elements link many regions of the protocerebrum to the calyces. A new type of touch- sensitive centrifugal neuron has been identified terminating in the pedunculus. The dendrites of this afferent reside in satellite neuropil, beneath the mushroom body's medial lobe, which is supplied by collaterals from medial lobe efferent neurons and by terminals from the central complex. The role of this centrifugal cell in odorant sampling is considered. Golgi impregnation identifies other afferents in proximal regions of the calyx (zone IIIA) that also originate from satellite neuropils, suggesting major reafference from the medial lobes channeled through this region. The relevance of multimodal supply to the calyx in odorant discrimination is discussed as are comparisons between mushroom body organization in this phylogenetically basal neopteran and other taxa.
• Strausfeld, N. J., & Yongsheng, L. i. (1999). Representation of the calyces in the medial and vertical lobes of cockroach mushroom bodies. Journal of Comparative Neurology, 409(4), 626-646.
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  PMID: 10376744;Abstract: Previous studies of honey bee and cockroach mushroom bodies have proposed that afferent terminals and intrinsic neurons (Kenyon cells) in the calyces are arranged according to polar coordinates. It has been suggested that there is a transformation by Kenyon cell axons of the polar arrangements of their dendrites in the calyces to laminar arrangements of their terminals in the lobes. Findings presented here show that cellular organization in the calyx of an evolutionarily basal neopteran, Periplaneta americana, is instead rectilinear, as it is in the lobes. It is shown that each calyx is divided into two halves (hemicalyces), each supplied by its own set of Kenyon cells. Each calyx is separately represented in the medial lobe where the dendritic trees of some efferent neurons receive inputs from one calyx only. Kenyon cell dendrites are arranged as narrow elongated fields, organized as rows in each hemicalyx. Dendritic fields arise from 14 to 16 sheets of Kenyon cell axons stacked on top of each other lining the inner surface of the calyx cup. A sheet consists of approximately 60 small bundles, each containing 5-15 axons that converge from the rim of the calyx to its neck. Each sheet contributes to a pair of laminae, one dark one pale, called a doublet, that extends through the mushroom body. Dark laminae contain Kenyon cell axons packed with synaptic vesicles. Axons in pale laminae are sparsely equipped with vesicles. By analogy with photoreceptors, and with reference to field potential recordings, it is speculated that dark laminae are continuously active, being modulated by odor stimuli, whereas pale laminae are intermittently activated. Timm's silver staining and immunocytology reveal a second type of longitudinal division of the lobes. Five layers extend through the pedunculus and lobes, each composed of subsets of doublets. Four layers represent zones of afferent endings in the calyces. A fifth (the γ layer) represents a specific type of Kenyon cell. It is concluded that the mushroom bodies comprise two independent modular systems, doublets and layers. Developmental studies show that new doublets are added at each instar to layers that are already present early in second instar nymphs. There are profound similarities between the mushroom bodies of Periplaneta, an evolutionarily basal taxon, and those of Drosophila melanogaster and the honey bee.
• Yongsheng, L. i., & Strausfeld, N. J. (1999). Multimodal efferent and recurrent neurons in the medial lobes of cockroach mushroom bodies. Journal of Comparative Neurology, 409(4), 647-663.
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  PMID: 10376745;Abstract: Previous electrophysiological studies of cockroach mushroom bodies demonstrated the sensitivity of efferent neurons to multimodal stimuli. The present account describes the morphology and physiology of several types of efferent neurons with dendrites in the medial lobes. In general, efferent neurons respond to a variety of modalities in a context-specific manner, responding to specific combinations or specific sequences of multimodal stimuli. Efferent neurons that show endogenous activity have dendritic specializations that extend to laminae of Kenyon cell axons equipped with many synaptic vesicles, termed 'dark' laminae. Efferent neurons that are active only during stimulation have dendritic specializations that branch mainly among Kenyon cell axons having few vesicles and forming the 'pale' laminae. A new category of 'recurrent' efferent neuron has been identified that provides feedback or feedforward connections between different parts of the mushroom body. Some of these neurons are immunopositive to antibodies raised against the inhibitory transmitter gamma-aminobutyric acid. Feedback pathways to the calyces arise from satellite neuropils adjacent to the medial lobes, which receive axon collaterals of efferent neurons. Efferent neurons are uniquely identifiable. Each morphological type occurs at the same location in the mushroom bodies of different individuals. Medial lobe efferent neurons terminate in the lateral protocerebrum among the endings of antennal lobe projection neurons. It is suggested that information about the sensory context of olfactory (or other) stimuli is relayed by efferent neurons to the lateral protocerebrum where it is integrated with information about odors relayed by antennal lobe projection neurons.
• Douglass, J. K., & Strausfeld, N. J. (1998). Functionally and anatomically segregated visual pathways in the lobula complex of a calliphorid fly. Journal of Comparative Neurology, 396(1), 84-104.
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  PMID: 9623889;Abstract: In dipteran insects, the lobula plate neuropil provides a major efferent supply to the premotor descending neurons that control stabilized flight. The lobula plate itself is supplied by two major parallel retinotopic pathways from the medulla: small-field, magnocellular afferents that are implicated in achromatic motion processing and Y cells that connect the medulla with both the lobula plate and the lobula. A third pathway from the medulla involves transmedullary (Tm) neurons, which provide inputs to palisades of small- field neurons in the lobula. Although, in their passage to the brain, many output neurons from the lobula plate are separated physically from their counterparts in the lobula, there is an additional class of lobula complex output neurons. This group is composed of retinotopic lobula plate-lobula (LPL) and lobula-lobula plate (LLP) cells, each of which has dendrites in both the lobula and the lobula plate. The present account describes the anatomy and physiology of exemplars of LPL and LLP neurons, a wide-field tangential neuron that is intrinsic to the lobula complex, and representatives of the Tm- and Y-cell pathways. We demonstrate novel features of the lobula plate, which previously has been known as a motion-collating neuropil, and now also can be recognized as supporting direction- or nondirection-specific responses to local motion, encoding of contrast frequency, and processing of local structural features of the visual panorama.
• Ito, K., Suzuki, K., Estes, P., Ramaswami, M., Yamamoto, D., & Strausfeld, N. J. (1998). The organization of extrinsic neurons and their implications in the functional roles of the mushroom bodies in Drosophila melanogaster meigen. Learning and Memory, 5(1-2), 52-77.
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  PMID: 10454372;PMCID: PMC311240;Abstract: Although the importance of the Drosophila mushroom body in olfactory learning and memory has been stressed, virtually nothing is known about the brain regions to which it is connected. Using Golgi and GAL4-UAS techniques, we performed the first systematic attempt to reveal the anatomy of its extrinsic neurons. A novel presynaptic reporter construct, UAS-neuronal synaptobrevin-green fluorescent protein (n-syb-GFP), was used to reveal the direction of information in the GAL4-labeled neurons. Our results showed that the main target of the output neurons from the mushroom body lobes is the anterior part of the inferior medial, superior medial, and superior lateral protocerebrum. The lobes also receive afferents from these neuropils. The lack of major output projections directly to the deutocerebrum's premotor pathways discourages the view that the role of the mushroom body may be that of an immediate modifier of behavior. Our data, as well as a critical evaluation of the literature, suggest that the mushroom body may not by itself be a 'center' for learning and memory, but that it can equally be considered as a preprocessor of olfactory signals en route to 'higher' protocerebral regions.
• Mizunami, M., Okada, R., Yongsheng, L. I., & Strausfeld, N. J. (1998). Mushroom bodies of the cockroach: Activity and identities of neurons recorded in freely moving animals. Journal of Comparative Neurology, 402(4), 501-519.
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  PMID: 9862323;Abstract: This article describes novel attributes of the mushroom bodies of cockroaches revealed by recording from neurons in freely moving insects. The results suggest several hitherto unrecognized functions of the mushroom bodies: extrinsic neurons that discriminate between imposed and self- generated sensory stimulation, extrinsic neurons that monitor motor actions, and a third class of extrinsic neurons that predict episodes of locomotion and modulate their activity depending on the turning direction. Electrophysiological units have been correlated with neurons that were partially stained by uptake of copper ions and silver intensification. Neurons so revealed correspond to Golgi-impregnated or Lucifer yellow-filled neurons and demonstrate that their processes generally ascend to other areas of the protocerebrum. The present results support the idea of multiple roles for the mushroom bodies. These include sensory discrimination, the integration of sensory perception with motor actions, and, as described in the companion article, a role in place memory.
• Mizunami, M., Weibrecht, J. M., & Strausfeld, N. J. (1998). Mushroom bodies of the cockroach: Their participation in place memory. Journal of Comparative Neurology, 402(4), 520-537.
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  PMID: 9862324;Abstract: Insects and other arthropods use visual landmarks to remember the location of their nest, or its equivalent. However, so far, only olfactory learning and memory have been claimed to be mediated by any particular brain region, notably the mushroom bodies. Here we describe the results of experiments that demonstrate that the mushroom bodies of the cockroach (Periplaneta americana), already shown to be involved in multimodal sensory processing, play a crucial role in place memory. Behavioral tests, based on paradigms similar to those originally used to demonstrate place memory in rats, demonstrate a rapid improvement in the ability of individual cockroaches to locate a hidden target when its position is provided by distant visual cues. Bilateral lesions of selected areas of the mushroom bodies abolish this ability but leave unimpaired the ability to locate a visible target. The present results demonstrate that the integrity of the pedunculus and medial lobe of a single mushroom body is required for place memory. The results are comparable to the results obtained from hippocampal lesions in rats and are relevant to recent studies on the effects of ablations of Drosophila mushroom bodies on locomotion.
• Strausfeld, N. J. (1998). Crustacean - Insect Relationships: The Use of Brain Characters to Derive Phylogeny amongst Segmented Invertebrates. Brain, Behavior and Evolution, 52(4--5), 186-206.
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  PMID: 9787219;Abstract: Conserved neural characters identified in the brains of a variety of segmented invertebrates and outgroups have been used to reconstruct phylogenetic relationships. The analysis suggests that insects and crustaceans are sister groups and that the 'myriapods' are an artificial construct comprising unrelated chilopods and diplopods. Certain elements of the optic lobes and mid-brain support the notion that insects are more closely related to crustaceans than they are to any other arthropods. However, deep optic neuropils and optic chiasmata are homoplastic in insects and crustaceans. The organization of olfactory pathways suggests that insect olfactory lobes originated late, probably first appearing in orthopteroid or blattoid pterygotes. The present results are discussed with respect to recent studies on early development of arthropod nervous systems and the fossil record.
• Strausfeld, N. J., Hansen, L., Yongsheng, L. i., Gomez, R. S., & Ito, K. (1998). Evolution, discovery, and interpretations of arthropod mushroom bodies. Learning and Memory, 5(1-2), 11-37.
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  PMID: 10454370;PMCID: PMC311242;Abstract: Mushroom bodies are prominent neuropils found in annelids and in all arthropod groups except crustaceans. First explicitly identified in 1850, the mushroom bodies differ in size and complexity between taxa, as well as between different castes of a single species of social insect. These differences led some early biologists to suggest that the mushroom bodies endow an arthropod with intelligence or the ability to execute voluntary actions, as opposed to innate behaviors. Recent physiological studies and mutant analyses have led to divergent interpretations. One interpretation is that the mushroom bodies conditionally relay to higher protocerebral centers information about sensory stimuli and the context in which they occur. Another interpretation is that they play a central role in learning and memory. Anatomical studies suggest that arthropod mushroom bodies are predominately associated with olfactory pathways except in phylogenetically basal insects. The prominent olfactory input to the mushroom body calyces in more recent insect orders is an acquired character. An overview of the history of research on the mushroom bodies, as well as comparative and evolutionary considerations, provides a conceptual framework for discussing the roles of these neuropils.
• Buschbeck, E. K., & Strausfeld, N. J. (1997). The relevance of neural architecture to visual performance: Phylogenetic conservation and variation in dipteran visual systems. Journal of Comparative Neurology, 383(3), 282-304.
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  PMID: 9205042;Abstract: In cyclorrhaphan flies, giant tangential neurons in the lobula plate are supplied by isomorphic arrays of evolutionarily conserved achromatic elementary motion detecting circuits originating in the retina. The arrangements among giant tangential neurons is characteristic of a taxon and can differ between taxa having different visual performances. Observations of 12 brachyceran and 4 nematoceran species have identified different behaviors associated with visually stabilized flight. Neuroanatomical comparisons between closely related species having different behaviors and phylogenetically distant species that have similar behaviors suggest that such differences relate to differences of giant tangential cell architecture in the lobula plate. These functionally related differences contrast to anatomical features that reflect phylogenetic affinities. For example, the lobula plates of robber flies, typified by ballistic flight behavior, all differ from other taxa in lacking cyclorrhaphan-type vertical motion- sensitive neurons; instead, they possess an extra complement of horizontal cells in their place. The results suggest that, although circuits that compute elementary motion are conserved across the Diptera, selective pressure has resulted in modifications of their target neurons, thus contributing to the wide variety of visual behaviors observed within this group of insects.
• Yongsheng, L. i., & Strausfeld, N. J. (1997). Morphology and sensory modality of mushroom body extrinsic neurons in the brain of the cockroach, Periplaneta americana. Journal of Comparative Neurology, 387(4), 631-650.
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  PMID: 9373016;Abstract: Mushroom bodies are paired centers in insect brains that are thought to be crucial in olfactory learning and memory. Early neuroanatomical descriptions suggested that the mushroom bodies comprise rather simple arrangements of nerve cells. Intrinsic neurons within each mushroom body were believed to receive olfactory afferents and to supply long, branched axons to extrinsic neurons that lead from the mushroom body into the protocerebrum. More recent suggestions that the mushroom bodies integrate several sensory modalities find support from intracellular and extracellular recordings of extrinsic neurons in the brains of crickets, honey bees, and cockroaches. Here, we describe two major classes of extrinsic neurons, simple and complex cells, in the mushroom bodies of the cockroach Periplaneta americana. Each class is defined by its pattern of branching in the brain. Simple neurons correspond to extrinsic neurons described from other species that have one set of dendrites only within the mushroom bodies. Complex extrinsic neurons possess dendrite-like branches within and outside the mushroom bodies. This arrangement may account in part for their observed multimodality, as might newly identified afferent neurons that terminate in the mushroom body lobes among the dendrites of extrinsic neurons and that respond to multimodal stimuli. Organizational complexity within the mushroom bodies is suggested by the grouping of intrinsic cell axons into discrete laminae. These are intersected by the block-like arrangements of dendritic fields of extrinsic neurons in a manner reminiscent of Purkinje cell dendrites intersecting parallel fibers in the cerebellum. The present results demonstrate that the cockroach mushroom body processes multimodal sensory information and that its neural arrangements contribute to a precise architecture consisting of discrete longitudinal and transverse subdivisions.
• Buschbeck, E. K., & Strausfeld, N. J. (1996). Visual motion-detection circuits in flies: Small-field retinotopic elements responding to motion are evolutionarily conserved across taxa. Journal of Neuroscience, 16(15), 4563-4578.
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  PMID: 8764645;Abstract: The Hassenstein-Reichardt autocorrelation model for motion computation was derived originally from studies of optomotor turning reactions of beetles and further refined from studies of houseflies. Its application for explaining a variety of optokinetic behaviors in other insects assumes that neural correlates to the model are principally similar across taxa. This account examines whether this assumption is warranted. The results demonstrate that an evolutionarily conserved subset of neurons corresponds to small retinotopic neurons implicated in motion-detecting circuits that link the retina to motion-sensitive neuropils of the lobula plate. The occurrence of these neurons in basal groups suggests that they must have evolved at least 240 million years before the present time. Functional contiguity among the neurons is suggested by their having layer relationships that are independent of taxon-specific variations such as medulla stratification, the shape of terminals or dendrites, the presence of other taxon-specific neurons, or the absence of orientation-specific motion-sensitive levels in the lobula plate.
• Douglass, J. K., & Strausfeld, N. J. (1996). Visual motion-detection circuits in flies: Parallel direction- and non- direction-sensitive pathways between the medulla and lobula plate. Journal of Neuroscience, 16(15), 4551-4562.
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  PMID: 8764644;Abstract: The neural circuitry of motion processing in insects, as in primates, involves the segregation of different types of visual information into parallel retinotopic pathways that subsequently are reunited at higher levels. In insects, achromatic, motion-sensitive pathways to the lobula plate are separated from color-processing pathways to the lobula. Further parallel subdivisions of the retinotopic pathways to the lobula plate have been suggested from anatomical observations. Here, we provide direct physiological evidence that the two most prominent of these latter pathways are, indeed, functionally distinct: recordings from the retinotopic pathway defined by small-field bushy T-cells (T4) demonstrate only weak directional selectivity to motion, in striking contrast with previously demonstrated strong directional selectivity in the second, T5-cell, pathway. Additional intracellular recordings and anatomical descriptions have been obtained from other identified neurons that may be crucial in early motion detection and processing: a deep medulla amacrine cell that seems well suited to provide the lateral interactions among retinotopic elements required for motion detection; a unique class of Y-cells that provide small-field, directionally selective feedback from the lobula plate to the medulla; and a new heterolateral lobula plate tangential cell that collates directional, motion- sensitive inputs. These results add important new elements to the set of identified neurons that process motion information. The results suggest specific hypotheses regarding the neuronal substrates for motion-processing circuitry and corroborate behavioral studies in bees that predict distinct pathways for directional and nondirectional motion.
• Armstrong, J., Kaiser, K., Müller, A., Fischbach, K., Merchant, N., & Strausfeld, N. J. (1995). Flybrain, an on-line atlas and database of the Drosophila nervous system. Neuron, 15(1), 17-20.
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  PMID: 7619521;
• Douglass, J. K., & Strausfeld, N. J. (1995). Visual motion detection circuits in flies: Peripheral motion computation by identified small-field retinotopic neurons. Journal of Neuroscience, 15(8), 5596-5611.
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  PMID: 7643204;Abstract: Giant motion-sensitive tangential neurons in the lobula plate are thought to be cardinal elements in the oculomotor pathways of flies. However, these large neurons do not themselves compute motion, and elementary motion detectors have been proposed only from theory. Here we identify the forms, projections, and responses of small-field retinotopic neurons that comprise a well known pathway from the retina to the lobula plate. Already at the level of the second and third synapses beneath the photoreceptor layer, certain of these small elements show responses that distinguish motion from flicker. At a level equivalent to the vertebrate inner plaxiform layer (the fly's outer medulla) at least one retinotopic element is directionally selective. At the inner medulla, small retinotopic neurons with bushy dendrites extending through a few neighboring columns leave the inner medulla and supply inputs onto lobula plate tangentials. These medulla relays have directionally selective responses that are indistinguishable from those of large-field tangentials except for their amplitude and modulation with contrast frequency. Centrifugal neurons leading back from the inner medulla out to the lamina also show orientation-selective responses to motion. The results suggest that specific cell types between the lamina and inner medulla correspond to stages of the Hassen-stein-Reichardt correlation model of motion detection.
• Gilbert, C., Gronenberg, W., & Strausfeld, N. J. (1995). Oculomotor control in calliphorid flies: Head movements during activation and inhibition of neck motor neurons corroborate neuroanatomical predictions. Journal of Comparative Neurology, 361(2), 285-297.
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  PMID: 8543663;Abstract: In tethered flying flies, moving contrast gratings or small spots elicit head movements which are suited to track retinal images moving at velocities up to 3,000°/sec (about 50 Hz contrast frequency for gratings of spatial wavelength 15°). To investigate the neural basis of these movements we have combined videomicroscopy with electrophysiological stimulation and recording to demonstrate that excitation of prothoracic motor neurons projecting in the anterodorsal (ADN) and frontal nerves (FN), respectively, generates the yaw and roll head movements measured behaviorally. Electrical stimulation of the ADN produces head yaw. The visual stimuli which excite the two ADN motor neurons (ADN MNs) are horizontal motion of gratings or spots moving clockwise around the yaw axis in the case of the right ADN (counterclockwise for left ADN). Activity is inhibited by motion in the opposite direction. Spatial sensitivity varies in the yaw plane with a maximum between 0° and 40° ipsilaterally, but both excitation and inhibition are elicited out to 80° in the ipsilateral and contralateral fields. ADN MNs respond to contrast frequencies up to 15-20 Hz, with a peak around 2-4 Hz for grating motion in the excitatory or inhibitory directions. Electrical stimulation of the FN primarily elicits roll down to the ipsilateral side. The one FN MN consistently driven by visual stimulation is excited by downward motion and inhibited by upward motion at 80° azimuth in the ipsilateral visual field. At -80° contralateral, visual motion has the opposite effect: Upward is excitatory and downward is inhibitory. The FN MN is tuned to contrast frequencies in the same range as the ADN MNs, with peak sensitivity around 4 Hz. The functional organization of inputs to the ADN and FN is discussed with respect to identified visual interneurons and parallel pathways controlling motor output.
• Gronenberg, W., Milde, J. J., & Strausfeld, N. J. (1995). Oculomotor control in calliphorid flies: Organization of descending neurons to neck motor neurons responding to visual stimuli. Journal of Comparative Neurology, 361(2), 267-284.
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  PMID: 8543662;Abstract: In insects, head movements are mediated by neck muscles supplied by nerves originating in the brain and prothoracic ganglion. Extracellular recordings of the nerves demonstrate units that respond to visual stimulation of the compound eyes and to mechanosensory stimulation of the halteres. The number of neck muscles required for optokinetic eye movements in flies is not known, although in other taxa, eye movements can involve as few as three pairs of muscles. This study investigates which neck motor neurons are likely to be involved in head movements by examining the relationships between neck muscle motor neurons and the terminals visiting them from approximately 50 pairs of descending neurons. Many of these descending neurons have dendrites in neuropils that are associated with modalities other than vision, and recordings show that visual stimuli activate only a few neck motor neurons, such as the sclerite depressor neurons, which respond to local or wide- field, directionally specific motion, as do a subset of descending neurons coupled to them. The results suggest that, like in the vertebrate eye or the retinas of jumping spiders, optokinetic head movements of flies require only a few muscles. In addition to the importance of visual inputs, a major supply to neck muscle centers by nonvisual descending neurons suggests a role for tactile, gustatory, and olfactory signals in controlling head position.
• Strausfeld, N. J., Kong, A., Milde, J. J., Gilbert, C., & Ramaiah, L. (1995). Oculomotor control in calliphorid flies: GABAergic organization in heterolateral inhibitory pathways. Journal of Comparative Neurology, 361(2), 298-320.
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  PMID: 8543664;Abstract: In calliphorid Diptera, motor neurons mediating visually evoked head movements can be excited or inhibited by visual stimuli, depending on the directionality of the stimulus and whether it is in the ipsi- or contralateral visual field. The level at which inhibition occurs is of special interest because binocular activation of homolateral tangential neurons in the lobula plate demonstrates that excitatory interaction must occur between the left and right optic lobes. Recordings and dye fillings demonstrate a variety of motion-sensitive heterolateral pathways between the lobula plates, or between them and contralateral deutocerebral neuropil, which provides descending pathways to neck motor centers. The profiles of heterolateral tangential cells correspond to neurons stained by an antibody against γ-aminobutyric acid (GABA). Other GABA-immunoreactive interneurons linking each side of the brain correspond to uniquely identified motion- sensitive neurons linking the deutocerebra. Additional inhibitory pathways include heterolateral GABAergic descending and ascending neurons, as well as heterolateral GABAergic neurons in the thoracic ganglia. The functional significance of heterolateral GABAergic pathways was tested surgically by making selective microlesions and monitoring the oculomotor output. The results demonstrate an important new attribute of the insect visual system. Although lesions can initially abolish an excitatory or inhibitory response, this response is reestablished through alternative pathways that provide inhibitory and excitatory information to the same motor neurons.
• Yang, M. Y., Armstrong, J., Vilinsky, I., Strausfeld, N. J., & Kaiser, K. (1995). Subdivision of the drosophila mushroom bodies by enhancer-trap expression patterns. Neuron, 15(1), 45-54.
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  PMID: 7619529;Abstract: Phylogenetically conserved brain centers known as mushroom bodies are implicated in insect associative learning and in several other aspects of insect behavior. Kenyon cells, the intrinsic neurons of mushroom bodies, have been generally considered to be disposed as homogenous arrays. Such a simple picture imposes constraints on interpreting the diverse behavioral and computational properties that mushroom bodies are supposed to perform. Using a P[GAL4] enhancer-trap approach, we have revealed axonal processes corresponding to intrinsic cells of the Drosophila mushroom bodies. Rather than being homogenous, we find the Drosophila mushroom bodies to be compound neuropils in which parallel subcomponents exhibit discrete patterns of gene expression. Different patterns correspond to hitherto unobserved differences in Kenyon cell trajectory and placement. On the basis of this unexpected complexity, we propose a model for mushroom body function in which parallel channels of information flow, perhaps with different computational properties, subserve different behavioral roles. © 1995.
• Strausfeld, N. J., & Barth, F. G. (1993). Two visual systems in one brain: Neuropils serving the secondary eyes of the spider Cupiennius salei. Journal of Comparative Neurology, 328(1), 43-62.
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  PMID: 7679122;Abstract: Like other araneans, the wandering spider Cupiennius salei is equipped with one pair of principal eyes and three pairs of secondary eyes. Primary and secondary eyes serve two distinct sets of visual neuropils in the brain. This paper describes cellular organization in neuropils supplied by the secondary eyes, which individually send axons into three laminas resembling their namesakes serving insect superposition eyes. Secondary eye photoreceptors send axons to small-field projection neurons (L-cells) which extend from each lamina to supply three separate medullas. Each medulla is a vault of neuropil comprising only a few morphological types of neurons. These can be compared to a subset of retinotopic neurons in the medullas of calliphorid Diptera supplying giant motion-sensitive neurons in the lobula plate. In Cupiennius, neurons from secondary eye medullas converge at a single target neuropil called the 'mushroom body.' This region contains giant output neurons which, like their counterparts in the calliphorid lobula plate, lead to descending pathways that supply thoracic motor circuits. It is suggested that the cellular arrangements serving Cupiennius's secondary eyes are color independent pathways specialized for detecting horizontal motion. The present results do not support the classical view that the spider 'mushroom body' is phylogenetically homologous or functionally analogous to its namesake in insects.
• Strausfeld, N. J., Weltzien, P., & Barth, F. G. (1993). Two visual systems in one brain: Neuropils serving the principal eyes of the spider Cupiennius salei. Journal of Comparative Neurology, 328(1), 63-75.
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  PMID: 7679123;Abstract: Principal (anterior median) eyes of the wandering spider Cupiennius are served by three successive neuropils, the organization of which is distinct from those serving secondary eyes. Photoreceptors terminate in the first optic neuropil amongst second order neurons with overlapping dendritic fields. Second order neurons terminate at various depths in anterior median eye medulla where they are visited by bush-like dendritic trees of third order projection neurons. These supply tracts which extend into the 'central body.' This crescent-shaped neuropil lies midsagittally in the rear of the brain near its dorsal surface. It is organized into columns and it supplies both columnar and tangential efferents to other brain centers. The supply to and organization of the 'central body' neuropil is reminiscent of retinotopic neuropils supplying the lobula of insects. Channels to the 'central body' comprise one of two concurrent visual pathways, the other provided by the secondary eyes supplying the 'mushroom body.' We suggest that principal eye pathways may be involved in form and texture perception whereas secondary eyes detect motion, as is known for jumping spiders. Our data do not support Hanstrom's classical view that the 'central body' is specifically associated with web-building, nor that it is homologous to its namesake in insect brains.
• Gilbert, C., & Strausfeld, N. J. (1992). Small-field neurons associated with oculomotor and optomotor control in muscoid flies: Functional organization. Journal of Comparative Neurology, 316(1), 72-86.
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  PMID: 1573052;Abstract: In fleshflies, Sarcophaga bullata, intracellular recording and Lucifer yellow dye-filling have revealed small-field elements of sexually isomorphic retinotopic arrays in the lobula and lobula plate, the axons of which project to premotor channels in the deutocerebrum that supply head-turning and flight-steering motor neurons. The dendrites of the small-field elements visit very restricted oval areas of the retinotopic mosaic, comprising fields that are typically 6-8 input columns wide and 12-20 high. Their physiologically determined receptive fields are also small, typically 20° or less in diameter. The neurons are hyperpolarized in stationary illumination and are transiently depolarized by light OFF and to a lesser degree by light ON. Motion of a striped grating elicits a periodic excitation at the fundamental or second harmonic of the stimulus temporal contrast frequency. The arrangement of these elements in retinotopic arrays with their small receptive fields and flicker-sensitive dynamic properties make these neurons well suited for the position-dependent, direction-insensitive detection of small objects in the fly's visual field, which is known to drive fixation and tracking.
• Gronenberg, W., & Strausfeld, N. J. (1992). Premotor descending neurons responding selectively to local visual stimuli in flies. Journal of Comparative Neurology, 316(1), 87-103.
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  PMID: 1374082;Abstract: The responses of dorsal descending neurons suggest great versatility of the visual system in detecting features of the visual world. Although wide- field motion-sensitive neurons respond to symmetric visual flow fields presented to both eyes, other neurons are known to respond selectively to asymmetric movement of the visual surround. The present account distinguishes yet a third class of descending neurons (DNs) that is selectively activated by local presentation of moving gratings or small contrasting objects. Excitation of these DNs in response to local motion contrasts with their inhibitory responses to wide-field motion. The described DNs invade dorsal neuropil of the pro- and mesothoracic ganglia where they converge with other morphologically and physiologically characterized descending elements. Axon collaterals of DNs visit thoracic neuropil containing the dendrites of motor neurons supplying indirect neck and flight muscles. The present results are discussed with respect to the organization of small-field retinotopic outputs from the lobula, and with respect to the parallel projection of many information channels from the brain to the neck and flight motors.
• Strausfeld, N. J., & Gilbert, C. (1992). Small-field neurons associated with oculomotor control in muscoid flies: Cellular organization in the lobula plate. Journal of Comparative Neurology, 316(1), 56-71.
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  PMID: 1573051;Abstract: In muscoid flies, the lobula plate is the last station in the optic lobes for processing spectrally independent information from retinotopic afferents. Until recently, it was thought that most lobula plate neurons were color- insensitive wide-field tangential neurons that respond to direction-specific motion. It has been suggested that certain of these supply inputs to premotor descending neurons involved in the control of flight and head movements. The present account describes a Golgi and cobalt-silver analysis that reports evidence for additional lobula plate outputs, which are numerically complex and structurally elaborate. Beneath a retina with approximately 4,000 ommatidia, each of at least 15 populations of morphologically distinct small- field neurons comprises approximately 110-440 elements that contribute to an isomorphic neural assembly subtending the whole retina. Morphologically small-field efferents form three classes according to the origin of their axons and their arborization in the lobula plate and lobula. Neurons arising from the lobula plate, or shared by it and the lobula, visit dorsal descending neurons supplying the neck and flight motor in contrast to output neurons from the lobula, which project to ventral descending neurons supplying leg motor neuropils. The possible functional significance of small- field lobula plate outputs onto descending neurons in the dorsal deutocerebrum is discussed.
• Gilbert, C., & Strausfeld, N. J. (1991). The functional organization of male-specific visual neurons in flies. Journal of Comparative Physiology A, 169(4), 395-411.
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  PMID: 1723431;Abstract: Intracellular recording and Lucifer yellow dye filling of male fleshflies, Sarcophaga bullata, have revealed male-specific neurons in the lobula, the axons of which project to the origin of premotor channels supplying flight motor neurons. Dendrites of male-specific neurons visit areas of the retinotopic mosaic supplied by the retina's acute zone, which is used by males to keep the image of a conspecific female centered during aerial pursuit. Only males engage in high-speed acrobatic chases, and male-specific neurons are suspected to under-lie this behavior. Physiological determination of receptive fields of male-specific neurons substantiates the fields predicted from anatomical studies and demonstrates that they subtend the acute zone. Male-specific neurons respond in a manner predicted on theoretical grounds from observations of tracking behavior. Such properties include directional selectivity to visual motion and higher sensitivity to motion of small images than to wide-field motion. The present account substantiates and extends neuroanatomical evidence that predicts that male-specific lobula neurons comprise a distinct circuit mediating conspecific tracking. © 1991 Springer-Verlag.
• Gronenberg, W., & Strausfeld, N. J. (1991). Descending pathways connecting the male-specific visual system of flies to the neck and flight motor. Journal of Comparative Physiology A, 169(4), 413-426.
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  PMID: 1723432;Abstract: During sexual pursuit, male flies Sarcophaga bullata, stabilize the image of a pursued target on the dorso-frontal acute zone of their compound eyes. By retinotopic projection, this region is represented in the upper frontal part of the lobula where it is sampled by ensembles of male-specific motion- and flicker-sensitive interneurons. Intracellular recordings of descending neurons, followed by biocytin injection, demonstrate that male-specific neurons are dye-coupled to specific descending neurons and that the response characteristics of these descending neurons closely resemble those of male-specific lobula neurons. Such descending neurons are biocytin-coupled in the thoracic ganglia, revealing their connections with ipsilateral frontal nerve motor neurons supplying muscles that move the head and with contralateral basalar muscle motor neurons that control wing beat amplitude. Recordings from neck muscle motor neurons demonstrate that although they respond to movement of panoramic motion, they also selectively respond to movement of small targets presented to the male-specific acute zone. The present results are discussed with respect to anatomical and physiological studies of sex-specific interneurons and with respect to sex-specific visual behavior. The present study, and those of the two preceding papers, provide a revision of Land and Collett's hypothetical circuit underlying target localization and motor control in males pursuing females. © 1991 Springer-Verlag.
• Strausfeld, N. J. (1991). Structural organization of male-specific visual neurons in calliphorid optic lobes. Journal of Comparative Physiology A, 169(4), 379-393.
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  PMID: 1723430;Abstract: The superiority of male flies over female flies in locating and intercepting small rapidly moving targets has been ascribed to differences in their visual systems. In males, this sexual dimorphism is externally expressed by an area of high visual acuity called the acute zone. Selective cobalt uptake reveals 12 types of male-specific visual interneurons in the male lobula, the axons of which terminate in neuropil supplying premotor descending neurons to neck and flight motor circuits. The dendritic fields of the individual male-specific neurons can be extrapolated out into visual space to demonstrate that each is assigned a discrete area of the visual panorama. The dendritic fields of 10 of the 12 male-specific neurons subtend areas of the retina associated with the male acute zone. The functional significance of male-specific neurons is discussed with respect to their putative receptive field and a model circuit for target location by male flies. © 1991 Springer-Verlag.
• Strausfeld, N. J., & Lee, J. K. (1991). Neuronal basis for parallel visual processing in the fly.. Visual neuroscience, 7(1-2), 13-33.
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  PMID: 1931797;Abstract: Behavioral and electrophysiological studies of insects demonstrate both spectrally independent and chromatically dependent behaviors and interneurons. This account describes the neuroanatomical identification of two parallel retinotropic subsystems, one supplying descending channels to spectrally independent neck and flight motor circuits, the other supplying polychromatic channels to neuropils associated with leg motor circuits in the thoracic ganglia. In the compound eye, two classes of photoreceptors contribute to each of several thousand sampling units. High-sensitivity, chromatically uniform short-axon photoreceptors (R1-R6) supply the lamina's external plexiform layer and are presynaptic to L1, L2 efferents. These project in parallel with a second system of trichromatic long-axon receptors and the L3 efferent. Both pathways supply columns of the medulla, equal in number to ommatidia. Golgi and cobalt-silver impregnation demonstrates that neurons from the medulla diverge to two deeper regions, the lobula plate and lobula, the former a thin tectum of neuropil dorsal to the more substantial lobula. Layer relationships between medulla neurons and their afferent supply suggest that the lobula plate and lobula are each supplied by one or the other, but not both, of the two parallel subsystems. Independence of the two parallel pathways is suggested by ablation of the photoreceptor layer leading to selective degeneration of the motion-sensitive lobula plate neuropil. In addition, octets of small-field neurons associated with the R1-R6/L1, L2 pathway give rise to synaptic complexes with motion-sensitive neurons of the lobula plate. A variety of behavioral and electrophysiological studies provide supporting evidence that certain insects possess parallel visual pathways comparable to the magnocellular and parvocellular subsystems of primates.
• Gronenberg, W., & Strausfeld, N. J. (1990). Descending neurons supplying the neck and flight motor of Diptera: Physiological and anatomical characteristics. Journal of Comparative Neurology, 302(4), 973-991.
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  PMID: 1707070;Abstract: In Diptera, dorsal neuropils of the pro-, meso-, and metathoracic ganglia supply motor neurons to neck and flight muscles. Motor circuits are supplied by more than 50 pairs of descending neurons (DNs) whose dendritic trees in the brain are restricted to dorsal neuropils of the deutocerebrum where they are grouped together into discrete clusters. Each cluster is visited by wide-field motion-sensitive neurons and by morphologically small-field retinotopic elements. This organization suggests that flight descending neurons should respond to complex stimuli reflecting panoramic movement and small-field motion. Intracellular recordings, combined with dye filling, confirm this. Certain descending neurons responding to visual flow fields terminate bilaterally in superficial pterothoracic neuropils, at the level of indirect (power) flight muscle motor neurons. Other DNs terminate laterally, and provide segmental collaterals to areas containing neck and direct (steering) flight muscle motor neurons. Such DNs are activated by wide-field directional stimuli corresponding to pitch, roll, or yaw, and to small-field stimuli. Appropriate directional mechanosensory stimuli also activate dorsal descending neurons. The significance of dorsal descending neurons for the control of flight is discussed and compared with studies on course deviation neurons in other insects. It is suggested that, in Diptera, dorsal descending neurons may separately be involved in the control of velocity, stabilization, and steering manoeuvres.
• Lee, J. K., & Strausfeld, N. J. (1990). Structure, distribution and number of surface sensilla and their receptor cells on the olfactory appendage of the male moth Manduca sexta. Journal of Neurocytology, 19(4), 519-538.
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  PMID: 2243245;Abstract: Distribution and neuronal organization of sensilla on the surface of the annulate flagellar segment of the antenna of the male Manduca sexta were studied by scanning and transmission electron microscopy. Nine types of sensilla were identified and their bipolar neurons ascribed to specific sensory modalities on the basis of their cuticular and dendritic morphology. Cuticle morphology identifies two types of sensilla trichodea, two types of sensilla basiconica and one type of sensillum coeloconicum. Certain of these olfactory sensilla are further subdivided on the basis of their dendritic structures. One type of sensillum chaeticum was interpreted as a contact chemoreceptor. A second type of sensillum coeloconicum and a styliform sensilla complex were interpreted as bimodal hygro- and thermosensilla. A second species of sensillum chaeticum serves mechanosensation. Counts from annuli situated about midway along the flagellum revealed a total of about 2200 sensilla supplied by approximately 5160 sensory neurons. A conservative estimate suggests that a male antenna with 85-90 annuli provides the flagellar nerve with at least 3.6 × 105 receptor axons, a number that exceeds previous estimates by almost 50% Each species of receptor has a characteristic location on the annulus. Of the 2100 or so sensilla situated on the dorsal, ventral and the leading edge surfaces, about 800 consist of male-specific type-I trichoids containing pheromone-sensitive receptors. Arciform arrays of these sensilla on the upper and lower surfaces of each annulus presumably optimize the capture and absorbtion of odour molecules. The trailing edge of the flagellum, which is thickly covered by scales and was assumed until now to lack receptors, contains both mechanosensitive and contact chemoreceptors. The modality of non-olfactory receptors is considered with respect to similar elements that have been functionally identified in other species. The coexistence of non-olfactory sensilla with olfactory elements is discussed with respect to current knowledge of the organization of olfactory centres in the brain. © 1990 Chapman and Hall Ltd.
• Milde, J. J., & Strausfeld, N. J. (1990). Cluster organization and response characteristics of the giant fiber pathway of the blowfly Calliphora erythrocephala. Journal of Comparative Neurology, 294(1), 59-75.
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  PMID: 2324334;Abstract: Intersegmental descending neurons (DNs) link the insect brain to the thoracic ganglia. Iontophoresis of cobalt or fluorescent dyes reveals DNs as uniquely identifiable elements, the dendrites of which are situated within a characteristic region of the lateral deutocerebrum. Here we demonstrate that DNs occur as discrete groups of elements termed DN clusters (DNCs). A DNC is a characteristic combination of neurons that arises from a multiglomerular complex in which the main components of each glomerulus are a characteristic ensemble of sensory afferents. Other neurons involved in the complex are local interneurons, heterolateral interneurons that connect DNCs on both sides of the brain, and neurons originating in higher centers of the brain. We describe the structure, relationships, and projections of eight DNs that contribute to a descending neuron cluster located ventrally in the lateral deutocerebrum, an area interposed between the ventral antennal lobes and the laterally disposed optic lobes. We have named this cluster the GDNC because its most prominent member is the giant descending neuron (GDN), which plays a cardinal role in the midleg 'jump' response and which is implicated in the initiation of flight. The GDN and its companion neurons receive primary mechanosensory afferents from the antennae, terminals of wide- and small-field retinotopic neurons originating in the lobula, and endings derived from sensory interneurons that originate in leg neuropil of the thoracic ganglia. We demonstrate that DNs of this cluster share morphological and functional properties. They have similar axon trajectories into the thoracic ganglia, where they invade functionally related neuropils. Neurons of the GDNC respond to identical stimulus paradigms and share similar electrophysiological characteristics. Neither the GDN nor other members of its cluster show spontaneous activity. These neurons are reluctant to respond to unimodal stimuli, but respond to specific combinations of visual and mechanosensory stimulation. These results suggest that in flies groups of morphologically similar DNs responding to context-specific environmental cues may cooperate in motor control.
• Strausfeld, N. J., & Gronenberg, W. (1990). Descending neurons supplying the neck and flight motor of Diptera: Organization and neuroanatomical relationships with visual pathways. Journal of Comparative Neurology, 302(4), 954-972.
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  PMID: 1707069;Abstract: In dipterous insects, a volume of behavioral and electrophysiological studies promote the contention that three wide-field motion-sensitive tangential neurons provide a necessary and sufficient input to specific channels that drive the torque motor during flight. The present studies describe the results of neuroanatomical investigations of the relationships between motion-sensitive neuropil in the fly optic lobes and descending neurons that arise from a restricted area of the brain and supply segmental neck and flight motor neuropil. The present observations resolve at least 50 pairs of descending neurons supplying flight motor centers in the thoracic ganglia. The majority of descending neurons receive a distributed output from horizontal motion-sensitive neurons. However, the same descending neurons are also visited by numerous small-field retinotopic neurons from the lobula plate as well as hitherto undescribed small tangential neurons. Neuroanatomical studies, using cobalt, Golgi, and Texas red histology, demonstrate that these smaller inputs onto descending neurons have dendrites that are organized at specific strata in retinotopic neuropil and that these correspond to horizontal and vertical motion sensitivity layers. Conclusions that only a restricted number of wide-field neurons are necessary and sufficient for visually stabilized flight may be premature. Rather, neuroanatomical evidence suggests that descending neurons to the flight motor may each be selectively tuned to specific combinations of wide- and small-field visual cues, so providing a cooperative descending network controlling the rich repertoire of visually evoked flight behavior.
• Milde, J. J., Seyan, H. S., & Strausfeld, N. J. (1987). The neck motor system of the fly Calliphora erythrocephala - II. Sensory organization. Journal of Comparative Physiology A, 160(2), 225-238.
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  Abstract: 1. The electrophysiology of the four paired nerves innervating the fly's neck muscles were examined by extra- and intracellular recording and staining with Lucifer Yellow. 2. Units that responded to moving black and white gratings and that were, therefore, termed 'visual' were recorded in all four neck muscle nerves. These visual motor neurons were direction-selective responding most vigorously to a single direction by excitation. 3. The preferred direction and the field of view of visual motor neurons was specific for each of the four neck muscle nerves and generally reflected an organization into horizontal- and vertical-motion-sensitive units. 4. The response characteristics of visual motor neurons corresponded to the structural relationship between their dendrites and visual interneurons in the lobula plate or terminals of descending neurons that were themselves associated with specific lobula plate neurons. 5. Visual units were only a small fraction of all neck motor neurons. A non-visual motor neuron responding to mechanical stimulation of wing and antenna and four mechanosensory fibre tracts associated with the prothoracic neck motor neuropil are described in detail. © 1987 Springer-Verlag.
• Strausfeld, N. J., & Seyan, H. S. (1987). Resolution of complex neuronal arrangements in the blowfly visual system using triple fluorescence staining. Cell and Tissue Research, 247(1), 5-10.
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  Abstract: Consecutive application of the fluorescent dyes, Texas Red and Lucifer Yellow, followed by nuclear staining with Bisbenzimide, reveals spatial relationships between individual neurons and relationships between their cell bodies and the perikaryal rind. The method is particularly useful for light-microscopical studies of complex interrelationships between identified neurons. The method has specific advantages over intraneuropil staining with cobalt or with HRP. These advantages are: simplicity, speed, information content, and aesthetic considerations. © 1987 Springer-Verlag.
• Strausfeld, N. J., Seyan, H. S., & Milde, J. J. (1987). The neck motor system of the fly Calliphora erythrocephala - I. Muscles and motor neurons. Journal of Comparative Physiology A, 160(2), 205-224.
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  Abstract: 1. The organization of muscles that move the head was analysed from serial-section reconstructions of whole animals. Muscle innervation was resolved by reduced silver and ethyl gallate staining or by cobalt or Lucifer Yellow fills from single motor terminals at identified muscles. 2. The organization of cuticular attachments for neck muscles, and the arthrology of joints between the rear of the head and cervical sclerites of the prothorax, was analysed from cleared exoskeletons. 3. As a rule, muscle blocks consist of two or more single muscles each supplied by only one motor neuron. Motor neurons supplying associated muscles of a block share the same peripheral motor nerve and have dendrites in a common area of neuropil. 4. The complex shape of motor neuron dendrites suggests that a variety of sensory fibres and interneurons converge on them. This is confirmed by observations of inputs from the halteres and prosternal organs, from hair receptor fields on the notum, and from chordotonal organs in the prothorax. 5. Cobalt coupling reveals that certain neck motor neurons receive input either from visual interneurons or from descending neurons that relay visual information. © 1987 Springer-Verlag.
• Bacon, J. P., & Strausfeld, N. J. (1986). The dipteran 'Giant fibre' pathway: neurons and signals. Journal of Comparative Physiology A, 158(4), 529-548.
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  Abstract: 1. The uniquely identifiable pair of giant descending neurons of Musca domestica and Calliphora erythrocephala are compared and described in relation to homologues in Drosophila. 2. Cobalt coupling in the giant fibre system suggests that giant descending neurons receive inputs from antennal mechanosensory afferents and small-field visual interneurons. 3. In Musca and Calliphora, terminals of giant descending neurons invade several discrete areas of neuropil. This is in contrast to Drosophila where homologous neurons have a relatively simple terminal. 4. Despite differences in morphology, in all three species a homologous terminal region is cobalt-coupled to the largest of three motorneurons supplying the second leg's tergotrochanteral muscle. 5. Sensory connections revealed anatomically were confirmed electrophysiologically by intracellular recording and dye-filling. Mechanosensory inputs from the ipsilateral antenna, and small field motion stimuli, or light 'on' and 'off' stimuli to the ipsilateral compound eyes, produce subthreshold activation in the giant descending neuron. 6. As in Drosophila, light 'on' or 'off' stimuli presented to white-eyed mutants of Musca and Calliphora elicit a spiking response in the giant descending neuron. In red-eyed flies, spikes could only be routinely induced by electrical stimulation across the head between the compound eyes or by releasing the cell from hyperpolarization. 7. Double recordings from the giant (intracellular combined with lucifer or cobalt iontophoresis for cell identification) and from the tergotrochanteral motorneuron (extracellular in muscle) show that a spike in the giant neuron is usually sufficient to drive a spike in the tergotrochanteral muscle. Latencies are short, as reported in Drosophila. Releasing the giant from hyperpolarization can result in a motorneuron spike in the absence of a spike in the giant: this suggests the presence of an electrical synapse. 8. Spiking in the tergotrochanteral muscle and the giant can occur independently of each other. Thus, this interneuron alone is neither necessary nor invariably sufficient for initiating 'escape behaviour' in the species studied. This is also corroborated by the structure of tergotrochanteral motorneurons whose extensive dendrites receive a variety of other inputs. © 1986 Springer-Verlag.
• Milde, J. J., & Strausfeld, N. J. (1986). Visuo-motor pathways in arthropods - Giant motion-sensitive neurons connect compound eyes directly to neck muscles in blowflies (Calliphora erythrocephala). Naturwissenschaften, 73(3), 151-154.
• Babu, K., Barth, F. G., & Strausfeld, N. J. (1985). Intersegmental sensory tracts and contralateral motor neurons in the leg ganglia of the spider Cupiennius salei Keys. Cell and Tissue Research, 241(1), 53-57.
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  Abstract: Cobalt filling into spider legs reveals plurisegmental receptor endings and the plurisegmental origin of motor neurons. Motor neuron dendrites are organized into two domains, one interacting with plurisegmental receptors, the other arborizing within the lateral neuropil of the leg neuromere. The intersegmental organization of both motor and sensory elements supports behavioural studies demonstrating inhibitory connections between legs. © 1985 Springer-Verlag.
• Strausfeld, N. J., & Bassemir, U. K. (1985). Lobula plate and ocellar interneurons converge onto a cluster of descending neurons leading to neck and leg motor neuropil in Calliphora erythrocephala. Cell and Tissue Research, 240(3), 617-640.
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  Abstract: In the fly, Calliphora erythrocephala, a cluster of three Y-shaped descending neurons (DNOVS 1-3) receives ocellar interneuron and vertical cell (VS4-9) terminals. Synaptic connections to one of them (DNOVS 1) are described. In addition, three types of small lobula plate vertical cell (sVS) and one type of contralateral horizontal neuron (Hc) terminate at DNOVS 1, as do two forms of ascending neurons derived from thoracic ganglia. A contralateral neuron, with terminals in the opposite lobula plate, arises at the DNOVS cluster and is thought to provide heterolateral interaction between the VS4-9 output of one side to the VS4-9 dendrites of the other. DNOVS 2 and 3 extend through pro-, meso-, and metathoracic ganglia, branching ipsilaterally within their tract and into the inner margin of leg motor neuropil of each ganglion. DNOVS 1 terminates as a stubby ending in the dorsal prothoracic ganglion onto the main dendritic trunks of neck muscle motor neurons. Convergence of VS and ocellar interneurons to DNOVS 1 comprises a second pathway from the visual system to the neck motor, the other being carried by motor neurons arising in the brain. Their significance for saccadic head movement and the stabilization of the retinal image is discussed. © 1985 Springer-Verlag.
• Strausfeld, N. J., & Bassemir, U. K. (1985). The organization of giant horizontal-motion-sensitive neurons and their synaptic relationships in the lateral deutocerebrum of Calliphora erythrocephala and Musca domestica. Cell and Tissue Research, 242(3), 531-550.
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  Abstract: Three giant horizontal-motion-sensitive (HS) neurons arise in the lobula plate. Their axons terminate ipsilaterally in the medial deutocerebrum and suboesophageal ganglion. Both Golgi impregnations and cobalt fills demonstrate that endings of the two HS cells, representing the upper and middle third of the retina, differ in shape and location from that of the HS cell subtending the lower third of the eye. This dichotomy is reflected by the terminals of a pair of centrifugal horizontal cells (CH), one of which invades lobula plate neuropil subtending the upper two-thirds of the retina. The other overlaps the dendrites of the HS cell subtending the lower one-third of the retina. The HS cells are cobalt-coupled to a variety of complexly arborizing descending neurons. In Musca domestica, gap-junction-like apposition areas have been observed between HS axon collaterals and descending neuron dendrites. The three HS cells also share conventional chemical synapses with postsynaptic elements, which include the dendritic spines of descending neurons. Unlike the giant vertical-motion-sensitive neurons of the lobula plate, whose relationships with descending neurons appear to be relatively simple, the horizontal cells end on a large number of descending neurons where they comprise one of several different populations of terminals. These descending neurons terminate within various centres of the thoracic ganglia, including neuropil supplying leg, neck, and flight muscle. © 1985 Springer-Verlag.
• Strausfeld, N. J., & Seyan, H. S. (1985). Convergence of visual, haltere, and prosternai inputs at neck motor neurons of Calliphora erythrocephala. Cell and Tissue Research, 240(3), 601-615.
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  Abstract: Neck muscles of Calliphora erythrocephala, situated in the anterior prothorax, are innervated on each side by 8 motor neurons arising in the brain (cervical nerve neurons, CN1-8) and at least 13 motor neurons arising in the prothoracic ganglion (anterior dorsal and frontal nerve neurons, ADN1,2 and FN1-11). Three prominent motor neurons (CN6 and FN1,2) are described in detail with special emphasis on their relationships with giant visual interneurons from the lobula plate, haltere interneurons, and primary afferents from the prosternal organs and halteres. These sensory organs detect head movement and body yaw, respectively. Neuronal relationships indicate that head movement is under multimodal sensory control that includes giant motion-sensitive neurons previously supposed to mediate the optomotor response in flying flies. The described pathways provide anatomical substrates for the control of optokinetic and yaw-incurred head movements that behavioural studies have shown must exist. © 1985 Springer-Verlag.
• Strausfeld, N. J., & Wunderer, H. (1985). Optic lobe projections of marginal ommatidia in Calliphora erythrocephala specialized for detecting polarized light. Cell and Tissue Research, 242(1), 163-178.
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  Abstract: The structure of ommatidia at the dorsal eye margin of the fly, Calliphora erythrocephala is specialized for the detection of the e-vector of polarized light. Marginal zone ommatidia are distinguished by R7/R8 receptor cells with large-diameter, short, untwisted rhabdomeres and long axons to the medulla. The arrangement of the R7 microvillar directions along the marginal zone is fan-shaped. Ommatidia lining the dorsal and frontal edge of the eye lack primary screening pigments and have foreshortened crystalline cones. The marginal ommatidia from each eye view a strip that is 5 °-20 ° contralateral to the fly's longitudinal axis and that coincides with the outer boundaries of the binocular overlap. Cobalt injection into the retina demonstrates that photoreceptor axons arising from marginal ommatidia define a special area of marginal neuropil in the second visual neuropil, the medulla. Small-field neurons arising from the marginal medulla area define, in turn, a special area of marginal neuropil in the two deepest visual neuropils, the lobula and the lobula plate. From these arise local assemblies of columnar neurons that relay the marginal zones of one optic lobe to equivalent areas of the opposite lobe and to midbrain regions from which arise descending neurons destined for the the thoracic ganglia. Optically, the marginal zone of the retina represents the lateral edge of a larger area of ommatidia involved in dorsofrontal binocular overlap. This binocularity area is also represented by special arrangements of columnar neurons, which map the binocularity area of one eye into the lobula beneath the opposite eye. Another type of binocularity neuron terminates in the midbrain. These neuronal arrangements suggest two novel features of the insect optic lobes and brain: (1) Marginal neurons that directly connect the left and right optic lobes imply that each lobe receives a common input from areas of the left and right eye, specialized for detecting the pattern of polarized light. (2) Information about the e-vector pattern of sky-light polarization may be integrated with binocular and monocular pathways at the level of descending neurons leading to thoracic motor neuropil. © 1985 Springer-Verlag.
• Strausfeld, N. J., Bassemir, U., Singh, R. N., & Bacon, J. P. (1984). Organizational principles of outputs from Dipteran brains. Journal of Insect Physiology, 30(1), 73-93.
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  Abstract: Two major classes of Descending Neurones (DNs) originate in fly cerebral ganglia: (1) uniquely identifiable DNs, most of which arise preorally in duetocerebral neuropil of the supraoesophageal ganglion, the brain proper (2) parallel projecting DNs (PDNs) most originating in the suboesophageal ganglion. Brain DNs receive inputs directly from sensory systems and indirectly via higher center and peptidergic interconnections of the protocerebrum. Direct inputs include primary mechanosensory afferents, first order relay neurones from the olfactory lobes and ocellar receptor cups, and higher order visual neurones that interact with retinotopic inputs from compound eyes. Uniquely identifiable DNs arising in the brain are arranged in uniquely identifiable clusters. Each cluster receives a unique combination of inputs which are shared wholly or in part by the dendritic trees of its constituent DNs. Axons arising from a cluster diverge to different targets in the thoracic ganglia. PDNs form groups of as many as 40 neurones, as determined from outgoing axon bundles. Dendrites of PDNs are thin and diffuse, and arborize amongst collaterals from through-going axons of descending neurones arising in the brain. Axon bundles of PDNs are typically organized in rather simple ladder-like patterns in thoracic ganglion. A third type of uniquely identifiable DN also arises in the suboesophageal ganglion but does not seem to be arranged in clusters. © 1984.
• Bassemir, U. K., & Strausfeld, N. J. (1983). Cytology of cobalt-filled neurons in flies: cobalt deposits at presynaptic and postsynaptic sites, mitochondria and the cytoskeleton. Journal of Neurocytology, 12(6), 949-970.
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  PMID: 6663324;Abstract: Combined light and electron microscopy of identified neurons requires an intracellular marker that is both photon opaque and has electron scattering properties. We describe results using cobalt chloride block intensified with silver as an intracellular label. The novelty of the method is its integration in tissue fixation, prior to dehydration, resulting in fine grain precipitates that resolve certain intracellular structures. Filled neurons are clearly distinguishable from unfilled profiles by cobalt-silver precipitates. Energy dispersive X-ray analysis confirms that silver is specifically deposited onto cobalt sulphide cores which are characteristically associated with microtubules, mitochondria, presynaptic and postsynaptic specializations and gap junction-like membrane appositions. © 1983 Chapman and Hall Ltd.
• Duve, H., Thorpe, A., & Strausfeld, N. J. (1983). Cobalt-immunocytochemical identification of peptidergic neurons in Calliphora innervating central and peripheral targets. Journal of Neurocytology, 12(5), 847-861.
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  PMID: 6196455;Abstract: Certain neurons of the blowfly, Calliphora erythrocephala, show immunoreactivity to anti-gastrin/cholecystokinin (CCK) COOH terminal specific antisera. However, as is common to immunocytochemical staining, much of the structure of the immunoreactive neurons escapes detection. We describe here whole-neuron identification by backfilling with Co2+ and subsequent silver reduction, combined with immunocytochemistry of the filled cells. Cobalt-silver filled neurons can be examined directly by fluorescence microscopy for the presence of a secondary, rhodamine-conjugated antibody linked to the primary one. Two peptide-containing pathways have been resolved, one leading out of the brain to the corpus cardiacum, the other innervating certain higher brain centres, such as the central body. Both arise from neurosecretory cells of the mid-brain. Immunoreactive peptidergic neurons leading, respectively, to the corpus cardiacum and to the central body have been matched to single nerve cells visualized by Golgi impregnation, cobalt backfilling or focal injection of cobalt into the brain. © 1983 Chapman and Hall Ltd.
• Strausfeld, N. J., & Bassemir, U. K. (1983). Cobalt-coupled neurons of a giant fibre system in Diptera. Journal of Neurocytology, 12(6), 971-991.
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  PMID: 6420522;Abstract: Certain intact nerve cells in flies can be filled with cobalt from presynaptic or postsynaptic neurons. This cobalt coupling is best demonstrated in giant fibre systems where the phenomenon was originally termed 'transsynaptic staining'. Fine structural analysis of silver-intensified, cobalt-coupled neurons indicates that the passage of cobalt ions occurs at gap junctions that are accompanied by conventional chemical synapses. Cobalt-coupled systems in dipterous insects are uniquely identifiable and can always be detected between the same kinds of neurons. The visualization of cobalt-coupled neurons allows the identification of functional pathways linking the brain to motor neuropils. © 1983 Chapman and Hall Ltd.
• Nässei, D., & Strausfeld, N. J. (1982). A pair of descending neurons with dendrites in the optic lobes projecting directly to thoracic ganglia of dipterous insects. Cell and Tissue Research, 226(2), 355-362.
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  PMID: 6812960;Abstract: The lobula descending neuron (LDN) of dipterous insects is a unique nerve cell (one on each side of the brain) that projects directly from the lobula complex of the optic lobes to neuropil in thoracic ganglia. In the supraoesophageal ganglia the LDN has two prominent groups of branches of which at least one is dendritic in nature. Postsynaptic branches are distributed in the lobula and some branches, the synaptic relations of which are not yet known, extend to the lobula plate. A second group of branches is found among dendrites of the descending neurons proper, in the lateral midbrain. The arborizations of LDN in the lobula (and lobula plate) map onto a retinotopic neuropil region subserving a posterior strip of the visual field of the compound eye. The arborizations in the lobula complex are extremely variable in size. The numbers of dendritic spines they possess vary greatly between left and right optic lobes of one animal, and between individual animals. © 1982 Springer-Verlag GmbH & Co. KG.
• Hausen, K., & Strausfeld, N. J. (1980). Sexually dimorphic interneuron arrangements in the fly visual system. Proceedings of the Royal Society of London - Biological Sciences, 208(1170), 57-71.
• Strausfeld, N. J. (1980). Male and female visual neurones in dipterous insects. Nature, 283(5745), 381-383.
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  Abstract: In many insects some visually guided behaviour patterns differ between the sexes. For example, male hoverflies and houseflies chase females in the air using visual cues but are not chased by females. Presumably information processing by nerve cells also differs. The genetic and histochemical identification of a brain area in Drosophila that must be male for male behaviour to occur suggests that circuits for sexual behaviour are localised. Recent anatomical studies of houseflies (Musca domestica) have demonstrated certain visual neurones present only in males. I report here results from another species (the blowfly, Calliphora erythocephala) demonstrating another kind of sexual difference of neural architecture in the visual system. In this fly dimorphism is expressed by differences in the shapes of analogous neurones in males and females, as well as by the presence of some cells in only one sex. The sexually dimorphic neurones of both sexes 'view' a region of the visual field coinciding with the region of binocular overlap.
• Strausfeld, N. J., & Singh, R. N. (1980). Peripheral and central nervous system projections in normal and mutant (bithorax) Drosophila melanogaster.. Basic life sciences, 16, 267-291.
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  PMID: 6161600;Abstract: Projections of axons from the wing, haltere and the head are described from silver intensified cobalt preparations of normal and bithorax mutant Drosophila. Dorsal projections from the homeotic wing into thoracic ganglia and to the brain are haltere-like. Ventral projections are wing-like. In general these results are in complete agreement with previous studies by Palka et al. and Ghysen. However, considerable variation of projection patterns is seen between individual mutant animals some of which were previously described only from mosaics (clones off bithorax sensory fibers into normal ganglia). Evidence for possible transformations of the third thoracic ganglion in mutants is therefore ambiguous.
• Strausfeld, N. J., & Ortega, J. C. (1977). Vision in insects: pathways possibly underlying neural adaptation and lateral inhibition. Science, 195(4281), 894-897.
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  PMID: 841315;Abstract: Like horizontal cells in vertebrate retinas, horizontal amacrine cells beneath the insect eye intervene between receptors and interneurons at the first level of synapses. Synaptic arrangements between amacrines and interneurons that give rise to regular networks of axon collaterals may explain recent electrophysiological observations of lateral inhibition beneath the insect retina. Neural adaptation mechanisms acting on single retinotopic channels or assemblies of channels can also be referred to reciprocal relationships between receptors and first order interneurons as well as to centrifugal cells from levels of so called photopic receptor endings.
• Strausfeld, N. J., & Obermayer, M. (1976). Resolution of intraneuronal and transynaptic migration of cobalt in the insect visual and central nervous systems. Journal of Comparative Physiology ■ A, 110(1), 1-12.
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  Abstract: Conventional cobalt chloride procedures, using either diffusion into cut nerves or application via an electrode, can only incompletely resolve nerve cells for light microscopical observation. Enhanced resolution can be obtained by the addition of small quantities of serum albumin to the cobalt chloride. This allows sufficient contrast many nerve cells and enhances the details of thin fibres and their appendages. That this should be possible is of cardinal importance for combined electrophysiological and structural studies. The present account also illustrates that in Dipterous insects there are certain conditions where cobalt chloride will move from one neuron into another. This movement is between functionally contiguous neurons and is here described from the visual system, with reference to electrophysiological studies that employ procion yellow identifications. Transynaptically filled neurons are only faintly resoluble in whole mounts. A block modification of the Timm's enhancement procedure is described which will reveal the finest details of neurons in thick sections and will also reveal nerve cells that have taken up minute quantities of CoCl2 after passage across at least two synapses. These observations are discussed with reference to their implications and applications for electrophysiological mappings of structural pathways. © 1976 Springer-Verlag.
• Campos-Ortega, J., & Strausfeld, N. J. (1973). Synaptic connections of intrinsic cells and basket arborizations in the external plexiform layer of the fly's eye. Brain Research, 59(C), 119-136.
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  PMID: 4747746;Abstract: The first synaptic region of the fly's visual system contains sets of climbing fibres enclosing each optic cartridge in a double basket-like arrangement of processes. The two sets of processes, termed α and β, can be separately identified by their fine structure. αfibres are more electron dense than β; they are postsynaptic to receptor endings from the retina and contain synaptic specializations apposed to epithelial cell membranes, to β fibres and to the distal processes of the L4 monopolar neurone. β is postsynaptic to receptors and to α. It has a lighter cytoplasm and contains peculiar glial invaginations called 'gnarls'. Degeneration experiments, where the optic chiasma between the 1st and 2nd synaptic regions has been severed, demonstrate that α fibres are intrinsic to the lamina. Golgi impregnation and electron microscopy of Golgi-impregnated cells have demonstrated that β fibres belong to a type of medulla-to-lamina cell, T1, whereas α fibres belong to an intrinsic (amacrine) cell in the lamina. The amacrine cells have wide fields through several cartridges. However, Golgi-EM studies show that each cartridge must be invaded by the processes of at least two cells. The synaptology of these elements is discussed with respect to previous data about the lamina, and certain analogies with the vertebrate plexiform layer are drawn. © 1973.
• Strausfeld, N. J., & Campos-Ortega, J. (1973). L3, the 3rd 2nd order neuron of the 1st visual ganglion in the "neural superposition" eye of Musca domestica. Zeitschrift für Zellforschung und Mikroskopische Anatomie, 139(3), 397-403.
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  PMID: 4707518;Abstract: Only three of the five types of monopolar cells which are present in each cartridge of the lamina have synaptic connections with receptor endings (R1-R6). Due to the distribution of their dendrites two of these (L1 and L2) contact the whole length of the six receptor endings of their cartridge whereas the third type (L3) contacts only their outer 2/3rds. Although these three cells may function as the second order neurons of the neurosuperposition eye, their anatomical relationship imply functional differences between them. © 1973 Springer-Verlag.
• Strausfeld, N. J., & Campos-Ortega, J. (1973). The L4 monopolar neurone: a substrate for lateral interaction in the visual system of the fly musca domestica (L). Brain Research, 59(C), 97-117.
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  PMID: 4747774;Abstract: Optic cartridges of the first synaptic region of the fly's visual system are interconnected by a set of collaterals derived from the L4 monopolar cells. These neurones are the only efferent monopolar cells to contact elements in more than one cartridge. Electron microscopy of Golgi-impregnated cells has shown that sets of distal (outer) processes of L4 contact, and are postsynaptic to, the α profiles of lamina intrinsic cells at single cartridges. L4's proximal (inner) collaterals, situated at the inner face of the lamina, contact the receptor terminals and the radial monopolar cells (L1 and L2) of its own and of two adjacent cartridges. One L4 meets components of 6 other L4 cells of 6 surrounding cartridges. Conventionally fixed material shows that the proximal collaterals of L4 are presynaptic to radial monopolar cells and some receptor endings as well as being pre-and postsynaptic to the other L4 neuronal components to which they extend, or which extend to them. The numbers of the distal processes postsynaptic to α fibres vary across the eye. There is a graded increase from back to front and from the dorsal and ventral poles of the eye towards its equator. © 1973.
• Campos-Ortega, J., & Strausfeld, N. J. (1972). The columnar organization of the second synaptic region of the visual system of Musca domestica L. - I. Receptor terminals in the medulla. Zeitschrift für Zellforschung und Mikroskopische Anatomie, 124(4), 561-585.
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  PMID: 5010818;Abstract: The projections of long visual fibres (R7+R8) from the retina to the medulla and their levels of termination in the second synaptic region have been studied with the aid of light and electron microscopy. Normal and degenerated material has revealed the fine structural characteristics of the long visual fibres as well as their orientations relative to those of a pair of first order interneuron terminals (monopolar cells). R7 and R8 project as pairs across the first optic chiasma. Their position equatorial to monopolar cells in the lamina is shifted to a polar position in the medulla via the chiasma. Their endings are situated at two levels: namely, R7 is deeper than R8. Like the short visual fibre endings in the lamina (R1-R6) the terminals of R7 and R8 in the medulla have synaptic specialisations throughout their length. The long visual fibres provide a point for point projection from the retina to the medulla and with monopolar cell terminals are arranged coincident with the three axes of the visual neuropil. © 1972 Springer-Verlag.
• Strausfeld, N. J. (1971). The organization of the insect visual system (Light microscopy) - I. Projections and arrangements of neurons in the lamina ganglionaris of Diptera. Zeitschrift für Zellforschung und Mikroskopische Anatomie, 121(3), 377-441.
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  Abstract: The structure of optic cartridges in the frontal part of the lamina ganglionaris (the outermost synaptic region of the visual system of insects) has been analysed from selective and reduced silver stained preparations. The results, obtained from studies on five different species of Diptera, confirm that six retinula cells, together situated in a single ommatidium, project to six optic cartridges in a manner no different from that described by Braitenberg (1967) from Musca domestica. Each optic cartridge contains five first order interneurons (monopolar cells) which project together to a single column in the second synaptic region, the medulla. The dendritic arrangement of two of these neurons (L1 and L2) indicates that they must make contact with all six retinula cell terminals of a cartridge (R1-R6). Two others (L3 and L5) have processes that reach to only some of the retinula cell endings. A fifth form of monopolar cell (L4) sometimes has an arrangement of processes which could establish contact with all six retinula cells: other cells of the same type may contact only a proportion of them. This neuron (L4) also has an arrangement of collaterals such as to allow lateral interaction between neigbouring optic cartridges. The processes of the other four monopolar cells (L1, L2, L3 and L5) are usually contained within a single cartridge. In addition to these elements there is a pair of receptor prolongations (the long visual fibres, R7 and R8) that bypasses all other elements of a cartridge, including the receptor terminals R1-R6, and finally terminates in the medulla. Four types of neurons, which are derived from perikarya lying just beneath or just above the second synaptic region, send fibres across the first optic chiasma to the lamina. Like all the other interneuronal elements of cartridges the terminals of these so-called "centrifugal" cells have characteristic topographical relationships with the cyclic arrangement of retinula cell terminals. Apart from the above mentioned neurons there is also a system of tangential fibres whose processes invade single cartridges but which together could provide a substrate for relaying information to the medulla derived from aggregates of cartridges. Optic cartridges contain at least 15 neural elements other than retinula cells. This complex structure is discussed with respect to the receptor physiology, as it is known from electrophysiological and behavioural experiments. The arrangements of neurons in cartridges is tentatively interpreted as a means of providing at least 6 separate channels of information to the medulla, four of which may serve special functions such as relaying color coded information or information about the angle of polarised light at high light intensities. © 1971 Springer-Verlag.
• Strausfeld, N. J. (1971). The organization of the insect visual system (Light microscopy) - II. The projection of fibres across the first optic chiasma. Zeitschrift für Zellforschung und Mikroskopische Anatomie, 121(3), 442-454.
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  Abstract: Each optic cartridge in the lamina of Diptera1 gives rise to a bundle of fibres composed of the prolongations of at least 11 neurons (two first order receptors, R7 and R8, five monopolar cells, L1-L5 and four "centrifugal" cells, T1, T1a, C2 and C3). The bundles project to the outer surface of the second synaptic region, the medulla. The projection patterns of the bundles means that a point for point map of the cartridge arrangement in the lamina is conferred on the medulla. The cross-over of bundles, along the horizontal axis of the eye, merely reverses the lamina map on the medulla. All eleven fibres that enter a bundle at the lamina are contained within it as far as the medulla. © 1971 Springer-Verlag.
• Strausfeld, N. J., & Braitenberg, V. (1970). The compound eye of the fly (Musca domestica): connections between the cartridges of the lamina ganglionaris. Zeitschrift für Vergleichende Physiologie, 70(2), 95-104.
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  Abstract: In addition to the three first order interneurons (L1, L2, L3) which are present in each optic cartridge of the lamina, a fourth type of interneuron (L4) has been discovered whose collaterals to other cartridges compose an orderly network arrangement of fibres under the lamina's inner face. © 1970 Springer-Verlag.

Presentations

• Strausfeld, N. J. (2017, 2017-3-23). Phenotypic homology of the insect and crustacean mushroom bodies. Invited talk: German Neurobiology Conference, Germany. Goettingen, Germany: University of Cologne.
• Strausfeld, N. J. (2017, June). FOSSIL BRAINS, TIME, AND CONSTANCY. Student Choice Keynote Lecturer at OHSU Research Week 2017. Oregon Health Science Center: OHSU Research Week 2017.
• Strausfeld, N. J. (2017, June). FOSSIL BRAINS, TIME, AND CONSTANCY. invited lecture. Univ. Maryland, Baltimore Campus, Dept. Biology: Dept. Biology.
• Strausfeld, N. J. (2017, June). Pancrustacean brains: origin, diversity and reconciling neural and molecular phylogenies. HHMI Janelia Research Conference. HHMI Janelia Research Campus: HHMI.
• Strausfeld, N. J. (2017, March). Genealogical Correspondence of Brain Centers across Pancrustacea: identifying the ancestral ground pattern. Twelfth Göttingen Meeting of the German Neuroscience Society. Göttingen, Germany: German Neuroscience Society.
• Strausfeld, N. J. (2017, March). Half a billion years of brain stability. Technau Festschrift 2017. Mainz, Germany: University of Mainz.
• Strausfeld, N. J. (2017, March, 2017). Brain homologies in Pancrustaceans. Insited speaker: Technau Festschrift. Mainz, germany: University of Mainz.
• Strausfeld, N. J. (2017, November). ARTHROPOD BRAINS AND THEIR CAMBRIAN ANTECEDENTS. invited lecture. Harvard: Harvard.
• Strausfeld, N. J. (2016, March 20 - 23). Functional implications of taxonomic distinctions of central complexes in Pancrustacea. Central Complex IV: A New Hope to Understand a Multifaceted Brain Region. Ashburn, Virginia: HHMI Janelia Research Campus.
• Strausfeld, N. J. (2016, May 15 - 18). A neuro-evolutionary understanding of circuit function: Fata morgana or structured destination?. Neuro-evo: A Comparative Approach to Cracking Circuit Function. Ashburn, Virginia: HHMI Janelia Research Campus.
• Strausfeld, N. J. (2016, November 17-18). Half a billion years of evolved stability and divergence. NSF Workshop: Comparative Principles of Brain Architecture and Functions. San Diego, California: National Science Foundation.
• Strausfeld, N. J. (2015, January). Tripartite Brains and Deep Time: Fossil Brains. FAREWELL MEETING HEINRICH REICHERT “NERVOUS SYSTEM DEVELOPMENT IN INVERTEBRATES”. Basel, Switzerland: Neurex.
• Strausfeld, N. J. (2015, July). The Evolution of the Arthropod Brain and the Fossil Record. The Future Is Now: Innovative Concepts in Neuroethology and New Technologies. Lucca, Italy: Gordon Research Conference on Neuroethology.
• Strausfeld, N. J. (2015, June). Excursions into Deep Time: Ancient Brains and their Genealogical Correspondences. 16th French Conference on Invertebrate Neurobiology. Gif-sur-Yvette, France: French Neuroscience Society.
• Strausfeld, N. J. (2015, September). Deep Time and Modern Brains. Invited Seminar, Queensland Brain Institute, University of Queensland, Brisbane, Australia. Brisbane, Australia: Queensland Brain Institute, University of Queensland.
• Strausfeld, N. J. (2014, April). Deep Time and Modern Brains. Invited lecture at Duquesne University, Dept. Biology.
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  Dates: 04/24/2014
• Strausfeld, N. J. (2014, April). Origin and evolution of mushroom bodies. Keynote lecture at HHMI Janelia Farms.
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  Date: 04/27
• Strausfeld, N. J. (2014, February). Deep Time and Modern Brains. Invited seminar at University of Illinois, Dept. Biology.
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  Dates: 02/25/2014
• Strausfeld, N. J. (2014, January 8). Deep Time and Modern Brains. Invited seminar at the Biocenter Colloquium, University of Wuerzburg. University of Wuerzburg: Biocenter.
• Strausfeld, N. J. (2014, January). Time Traveling: What Our Brains Share with Beetle Brains. UA Science Lecture Series: The Evolving Brain.
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  Date: 01/27
• Strausfeld, N. J. (2014, July). Invited lecture: Ecology, Predation, and Neural Ground Patterns in Deep Time. 11th International Congress of Neuroethology. Sapporo, Japan.
• Strausfeld, N. J. (2014, March). Deep Time and Modern Brains. Invited lecture at Yale University.
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  Dates: 03/06/2014
• Strausfeld, N. J. (2014, October). Deep Time and Modern Brains. 2014 MacArthur Fellows Forum.
• Strausfeld, N. J. (2014, September). Exceptionally Preserved Chengjiang Fossils Resolve Evolutionary Trajectories of Brain and Nervous System Typifying Panarthropoda. Keynote lecture at 4th International Palaeontological Congress, Mendoza, Argentina.
• Strausfeld, N. J. (2013, April). Arthropod brains: their origin, evolution, and what they share with brains of vertebrates. USCD Neuroscience Graduate Program Founder’s Day Lecture.
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  Dates: 04/02/2013
• Strausfeld, N. J. (2013, August). Origin, Elaboration and Homologies of Arthropod Visual Systems. International Conference on Insect Vision. Backaskog Slot, Sweden.
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  Dates: 08/01-08/08
• Strausfeld, N. J. (2013, Fall). Evolution of the insect brain. Cold Spring Harbor Drosophila course.
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  Dates: 07/05-07/07
• Strausfeld, N. J. (2013, Fall). Of prawns and people: the evolutionary correspondence of brains. Carl Friedrich von Siemens Foudation lecture. Munich, Germany.
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  Date: 11/21
• Strausfeld, N. J. (2013, March). Insects, vision, correspondences and genealogy: of fliesand felines. Insect Vision: Cells, Computation, and BehaviorJanelia Farm Research Campus.
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  Dates: 03/03-03/06
• Strausfeld, N. J. (2013, September). How old is the insect brain and how similar is it to ours?. The Nervous System of Drosophila melanogaster: from development to Function. Freiburg, Germany.
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  Dates: 09/26-09/29
• Strausfeld, N. J. (2013, September). “What” and “where” in sensory space: parallels between olfactory and visualperception. Keynote lecture at 1st International Workshop on "Odor spaces". Hannover, Germany.
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  Dates: 09/03-09/08
• Strausfeld, N. J., & Hirth, F. (2013, October). Deep homology of arthropod central complex and vertebrate basal ganglia. ESF-FENS Brain Conference: The Neurobiology of Action. Stresa, Italy: European Science Foundaion.
• Strausfeld, N. J. (2012, April). Towards a common framework to study the function of the insect central complex. HHMI Janelia Farms Campus meeting.
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  Dates: 04/15-04/18
• Strausfeld, N. J. (2012, December). Arthropod brains: their evolution and what they suggest about the brains of other phyla. Dept of EEB. University of Arizona. Tucson, AZ.
• Strausfeld, N. J. (2012, July). Circuit comprehension: a synthesis from studies of the insect visual system. Barcelona Cognition, Brain and Technology Summer School 2012. Barcelona, Spain.
• Strausfeld, N. J. (2012, July). Euro EvoDevo July. Euro EvoDevo July. Lisbon, Portugal.
• Strausfeld, N. J. (2012, July). Exploring the origins of higher cerebral centers and their vertebrate equivalents. Barcelona Cognition, Brain and Technology Summer School 2012. Barcelona, Spain.
• Strausfeld, N. J. (2012, July). Time travelling to find a brain. Barcelona Cognition, Brain and Technology Summer School 2012. Barcelona, Spain.
• Strausfeld, N. J. (2012, June). Arthropod Brain Evolution. Keynote lecture at Cold Spring Harbor Asia International Conference on Insect Neuroscience. Suzhou, China.
• Strausfeld, N. J. (2012, May). Identification of neural and sensory pathways in Cambrian fossils. Yunnan University Key Laboratory for Paleaontology. Kunming, China.
• Strausfeld, N. J. (2012, November). 2012-2013 Brains & Behavior Distinguished Lecturer Seminar Series. 2012-2013 Brains & Behavior Distinguished Lecturer Seminar Series. Atlanta, Georgia: Georgia State University.
• Strausfeld, N. J. (2012, September). Arthropod NeuroNetwork. Arthropod NeuroNetwork. Konstanz, Germany.

Reviews

• Strausfeld, N. J., Ma, X., & Edgecombe, G. D. (2016. Fossils and the Evolution of the Arthropod Brain(pp R989-R1000).
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  The discovery of fossilized brains and ventral nerve cords in lower and mid-Cambrian arthropods has led to crucial insights about the evolution of their central nervous system, the segmental identity of head appendages and the early evolution of eyes and their underlying visual systems. Fundamental ground patterns of lower Cambrian arthropod brains and nervous systems correspond to the ground patterns of brains and nervous systems belonging to three of four major extant panarthropod lineages. These findings demonstrate the evolutionary stability of early neural arrangements over an immense time span. Here, we put these fossil discoveries in the context of evidence from cladistics, as well as developmental and comparative neuroanatomy, which together suggest that despite many evolved modifications of neuropil centers within arthropod brains and ganglia, highly conserved arrangements have been retained. Recent phylogenies of the arthropods, based on fossil and molecular evidence, and estimates of divergence dates, suggest that neural ground patterns characterizing onychophorans, chelicerates and mandibulates are likely to have diverged between the terminal Ediacaran and earliest Cambrian, heralding the exuberant diversification of body forms that account for the Cambrian Explosion.

Others

• Strausfeld, N. J. (2015, March). International Meeting: Origin and evolution of the nervous system. Funded by the Royal Society of London.
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  Co-organized (with Frank Hirth, King's College London) an International Meeting at the Royal Society of London on Origin and evolution of the nervous system, and co-edited the resulting special issue of Philosophical Transactions of the Royal Society B (ISSN 0962-8436, Volume 370, Issue 1684, 19 December 2015).
• Strausfeld, N. J. (2015, March). International Meeting: Homology and convergence in nervous system evolution. Funded by the Royal Society of London.
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  Co-organized (with Frank Hirth, King's College London) an International Meeting at the Royal Society of London on Homology and convergence in nervous system evolution, and co-edited the resulting special issue of Philosophical Transactions of the Royal Society B (ISSN 0962-8436, Volume 371, Issue 1685, 5 January 2016).