Cortical circuit mechanisms of visual shape processing

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PROJECT SUMMARY Humans and other primates rely on using visual shape information to identify and interact with objects in the world. The goal of this project is to gain mechanistic insights into how the primate cerebral cortex processes visual shape information. Cortical area V4 is an ideal locus for these mechanistic studies because many V4 neurons are tuned for visual shape, showing preferences for convex or concave segments along an object's bounding contour. This tuning for visual shape is presumed to be a foundation for behaviorally relevant object representations, but we know little about its mechanistic implementation. Chiefly, we do not know which cortical pathways and cell types are responsible for generating this tuning in V4 neurons. In this project, we will begin to fill these knowledge gaps by employing viral vector-mediated, cell type-specific optogenetics in monkeys. In Aim 1, we will ask: How does visual shape processing in V4 depend on feedforward excitatory signals from earlier cortical areas V1 and V2? The experiments related to this aim will test the hypothesis that feedforward excitation from area V2 is the dominant factor in dictating the shape tuning of V4 neurons. In Aim 2, we will ask: How does visual shape processing in V4 depend on local inhibitory signals within this area? The experiments related to this aim will test the hypothesis that inhibitory neurons are tuned for shape, and that local inhibition sharpens the tuning of excitatory neurons. Accomplishing these aims will provide critical first insights into the role of feedforward excitation and local inhibition in visual shape processing. A deeper understanding of these cortical circuit mechanisms in primates has the potential to transform the way in which we treat disorders of form vision such as visual agnosia. Advancing optogenetic techniques for neural circuit dissection in monkeys will also facilitate the investigation of other complex brain functions that are specific to primates: an imperative for advancing basic science and human medicine.