Functional and cell-type specific axonal pathways in the primate brain

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Project Summary/Abstract Over the past decade, there have been transformative advances in three areas of mammalian neuroscience. First, our ability to record from large populations of neurons has dramatically increased with the advent of new electrode technologies and improved multiphoton imaging. Second, the study of brain connections in their entirety, connectomics, has come into its own as a field. Most recently, there has been a revolution in the classification of neuronal types, largely by probing which genes are translated into RNA in cells (transcriptomics). What is lacking is a way to bring these three fields together, particularly in the studies of non-human primates and humans. The goal of the current RFA is to create innovative tools for use in humans and non-human primates. In particular, two suggested topics are to develop: (1) “novel methods for tagging individual neurons such that cellular components of a functional circuit can be explored” and (2) “innovative approaches to bridge scales of experimental approach. Studies that can explore molecular and cellular mechanisms of neural activity in broader contexts are encouraged.” To achieve these goals, we present an innovative approach to characterize neuronal cell types in macaques and humans, combining transcriptomics, inter-areal connectivity and functional studies at multiple scales, from individual neurons to entire brains. We will build the necessary tools to create integrated atlases of individual brains that combine six modalities into a common reference frame: (1) functional MRI, to measure functional properties of brain areas at 0.5-1 mm resolution, (2) widefield optical imaging, to map bulk neuronal activity at the cortical surface with ~100 µm resolution, (3) multiphoton calcium imaging, to map neuronal activity in individual neurons across multiple cortical areas, (4) diffusion tensor imaging (DTI), to map axonal tracts in the white matter with 0.5-1 mm resolution, (5) “axonal connectomics”, to map projections of individual myelinated axons from efferent cell bodies to their postsynaptic targets, and (6) multiplexed FISH, to assay transcriptomic identities of the same cells whose physiology and projection targets have been defined. Data from first three modalities will be collected, starting with in vivo studies of macaques and correlated with subsequent analysis of brain tissue with the last three modalities. Only the last three steps will be used in the study of human brain tissue, although functional MRI could, in principle, be obtained from research institutions with appropriate programs for prospective studies.