Visual Stimulus Coding and Metabolic Demand in Macaque Primary Visual Cortex

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Project Summary/Abstract The relationships between neural response properties, their anatomical underpinnings, and the metabolic profile of neural tissue are key issues that define the normal functional architecture of the cerebral cortex. Understanding how these different systems are organized and work together is fundamental to neuroscientific research. Recent advances in optical imaging of cerebral activity have made it possible to record activity of both neuronal and metabolic dynamics simultaneously. In primate primary visual cortex (V1), the relationships between neuronal orientation and color selectivity have been related to distribution of the metabolic enzyme cytochrome oxidase (CO) and vascular dynamics. The pattern of CO distribution in macaque V1 is a defining characteristic of this brain area. In V1, metabolic demand varies locally and by layer, as evident by diffuse CO-dense patches of cortex surrounded by less dense CO regions in layer 2/3. The distribution of CO in neurons has also been shown to be related to the density and organization of the vasculature which supplies the cortical tissue with nutrients and metabolites. The long-established idea of how these systems interact suggests that strongly orientation tuned neurons reside in only CO interpatch regions while unoriented color tuned neurons reside exclusively in CO patches. However, recent research has shown that such a functional segregation is unlikely. Because earlier techniques failed to measure cone-specific and orientation-specific responses in the same cells and relate them to the CO pattern, new techniques—such as 2-photon imaging—are needed to develop an accurate picture of the functional organization of V1. In addition, the vasculature surrounding tuned neurons has been shown to have its own tuning through changes in vessel dilation and contraction, and therefore are expected to be related to the CO pattern if neural sensitivity to specific stimuli is locally organized in V1. The goal of this proposal is to characterize the interaction of neuronal visual stimulus tuning, CO compartment identity, and vascular dynamics in primate V1. In Aim 1 we will use multiphoton calcium imaging to record orientation and cone specific selectivity in V1 and align the imaged regions with histological sections of CO staining to determine how neurons with different response profiles are distributed among CO patch or interpatch regions. In Aim 2 we will examine whether vascular dynamics are related to cone-specific orientation selectivity and CO compartment identity. The findings of this study will give us comprehensive information on the basic organization of the V1 and fundamentally alter our understand of visual processing.