Regents Professor and Professor of Neuroscience, Ecology and Evolutionary Biology, Entomology, International Studies, and Adjunct Professor of Art
Director, Center for Insect Science
Ph.D. 1968, University College, London
Functional and anatomical analysis of the visual system - behavioral, electrophysiological, and developmental studies of a learning and memory center - evolutionary studies of arthropod brains
Four areas of research are being pursued in my laboratory. We also administer, with international collaborators in Japan and Germany, the NSF-supported Drosophila nervous system database FLYBRAIN (http://www.flybrain.org/)
Higher brain centers for learning and memory.The brains of insects are equipped with paired mushroom bodies— centers that, like the hippocampus, play a role in spatial learning and memory and in context-dependent sensory integration. We are studying the organization of mushroom bodies in the cockroach, Periplaneta americana, recording from identified neurons during multisensory stimulation. We are also investigating neuronal modification using paired stimuli that condition motor actions. Mushroom bodies are being investigated anatomically, with particular attention to ensembles of peptidergic neurons that subdivide the honey bee mushroom bodies into discrete parallel microprocessors that may play crucial roles in sensory association. Comparisons between mushroom body organization in advanced and primitive Hymenoptera suggest interesting parallels with the evolutionary elaboration of the vertebrate forebrain.
Comparative studies amongst taxa reveal common principles of organization. Information derived from one species can be confidently integrated with information derived from another. For example, although it is not feasible to obtain long-term intracellular recordings from neurons in Drosophila mushroom bodies, there are obvious similarities between their cellular arrangements and those in cockroaches.
Development of learning and memory neuropils. Regions of the brain specialized for learning and memory comprise intricate yet modifiable neural circuits. Studying how such circuits develop will provide insights into how neurons are arranged to provide substrates for sensory association and subsequent modifications of efferent neuron responses. Although not yet manipulatable using gene technology, the cockroach has certain advantages over Drosophila. It is an evolutionary basal taxon with many primitive features. Cockroaches develop through many instars (hemimetaboly), each being differently challenged by the sensory environment. The following are a few of the many questions that can be asked of this system. How does the internal network of the mushroom bodies develop, and which connections are necessary and sufficient for learning to occur? What roles do hormones play in the proliferation and differentiation of the many hundreds of thousands of intrinsic neurons in the mushroom bodies? To what sensory combinations are mushroom body output neurons tuned at different developmental stages, and are differences of stimulus selectivity associated with specific age-related alterations of intrinsic neuron circuits?
Brain evolution and Arthropod Phylogeny. Arthropods comprise the most species-rich phylum, and enormous challenges to systematists in resolving the evolutionary history of this ancient group. Traditionally, hypotheses regarding the relationships of the major arthropod clades have focused on suites of morphological characters whereas modern phylogenomics relies on large amounts of molecular sequence data to infer evolutionary relationships. However, studies since 1995 have shown that brain organization is remarkably consistent within certain groups, irrespective of differences of external morphology. For example, the brains of coleopteran insects share numerous structural similarities that are distinct from those that typify the brains of, say, Diptera or Lepidoptera. The same is true for Orders of Crustacea, Chelicerata, and Myriapoda. Because neural architectures are so conserved, they can serve as diagnostics for deriving possible phylogenetic relationships amongst these invertebrates. Hennigian cladistics provides the most neutral route to resolving such relationships. Defined structural features (characters), such as neurofibrillar architectures, types of tracts, heterolaterality of neuropils, cell body arrangements, and many more, are scored as present or absent in representative taxa across the two protostome clades — Ecdysozoa and Lophotrochozoa — and selected outgroup species, thereby inferring relatedness among taxa using tools such as PAUP (Phylogenetic Analysis Using Parsimony). Cladistic analyses support the view that Hexapoda are most closely related to Malacostraca. These results conform to phylogenies published recently (2010) by certain other laboratories using molecular sequence data.
Such comparisons are invaluable for investigating neural adaptations, convergence, and filter matching between a brain’s organization and its ecology. For example, in the fly visual system, a specialized achromatic neuropil called the lobula plate, contains systems of wide-field neurons that collate information about visual flow fields over the retina. These neurons supply pathways involved in visual balance. An agile and highly visual species of isopod crustacean also possesses a lobula plate equipped with wide-field neurons. Because isopods are separated from flies by at least 400 million years, it would appear that these similar centers have evolved independently. However, comparisons across a wide variety of Crustacea reveal that these neuropils are ubiquitous and may represent the earliest neural network to have evolved beneath the compound eye. Related to this work is an ongoing study on fossilized stem group crustaceans from the Lower Mid-Cambrian, certain of which show well-preserved compound eyes, traces of brain and ganglia, and details of sensory fields and their constituent sensilla. Together, these elements suggest that quite complex nervous system must have already evolved by the Mid-Cambrian to deal with a rich sensory world.
Functional organization in visual systems. Research on the organization of the insect visual system focuses on the functional dissection of neural circuits that compute directional motion during flight, and which are distinct from the organization of neurons that are tuned to small-field orientation during visual discrimination by the walking or resting animal. Our research on the latter employs intracellular recording from extremely small retinotopic neurons that have restricted receptive fields and which respond to motion and direction cues with either spiking or non-spiking (graded) potentials. Immunocytology and cell marking are used to elucidate the distribution of transmitter substances in this system, with the aim of determining what transmitters are used by identified neurons and how these are interconnected. Collaborations with Professor Charles Higgins in the Department of Electrical and Computer Engineering have resulted in printed circuits on silicon chips based these studies. These circuits are able to resolve directional motion across a range of velocities and ambient light intensities. Current studies now focus on the integration of visual and other sensory inputs at levels beneath the optic lobes, including the central body complex, which is a neuropil involved in the control of motor actions.
Selected Recent Publications
Strausfeld NJ 2010. Neurons and circuits that contribute to the detection of directional motion across the retina of the fly. Handbook of Brain Microcircuits. Eds: Gordon M. Shepherd and Sten Grillner. Oxford University Press.
Strausfeld NJ 2009. Brain organization and the origin of insects: an assessment. Proc Roy Soc Biol Sci 276:1929-37.
Brown S, Strausfeld N 2009. The effect of age on a visual learning task in the American cockroach. Learn Mem. 16:210-23.
Rister J, Pauls D, Schnell B, Ting CY, Lee CH, Sinakevitch I, Morante J, Strausfeld NJ, Ito K, Heisenberg M. 2007. Dissection of the peripheral motion channel in the visual system of Drosophila melanogaster. Neuron, 56:155-70
Strausfeld NJ, Sinakevitch I, Okamura JY. 2007. Organization of local interneurons in optic glomeruli of the dipterous visual system and comparisons with the antennal lobes. Dev Neurobiol, 67:1267-88
Lent DD, Pinter M, Strausfeld NJ. 2007. Learning with half a brain. Dev Neurobiol, 67:740-51
Strausfeld NJ Okamura JY. 2006. Visual system of calliphorid flies: Organization of optic glomeruli and their lobula complex efferents. J Comp Neurol, 500:166-188
Sinakevitch I, Strausfeld NJ. 2006. Comparison of octopamine-like immunoreactivity in the brains of the fruit fly and blow fly. J Comp Neurol, 494:460-75
Loesel R, Nassel DR, Strausfeld NJ. 2002. Common design in a unique midline neuropil in the brains of arthropods. Arthropod Struct Dev, 31:77-91
Strausfeld NJ. 2002. Organization of the honey bee mushroom body: representation of the calyx within the vertical and gamma lobes. J Comp Neurol, 450:4-33
Publications: links to abstracts on PubMed (pdf)
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