Visual perception is mediated by complex interaction amongst urons in the retina, visual cortex and subcortical brain structured. The importance of vision to humans and other primates in reflected in the enormous percentage of cerebral cortex devoted to processing visual information. Thus deficits in visual processing are particularly debilitating and arise from abnormalities not only in the eye, but also in cortical circuitry, For example, strabismus or amblyopia during childhood can have long-lasting effects on the cortical circuits that process visual information. There is also evidence that some forms of dyslexia result from central visual system abnormalities. The proposed studies are aimed at understanding the organization of neural circuits within and between the visual cortical areas V1 and V2, with the broader objective of contributing to understanding how neural circuits mediate the computations that underlie visual perception. In particular, these studies aim to identify: (1) how local circuits in V1 mediate integration and/or segregation of information arising from """"""""parallel M and P retino-geniculate pathways; 2) whether V1 neurons receiving different combinations of M and P input project in turn to different functional compartments in V2; (3) the sources of local functional input to individual neurons in the deep layers of V1 and whether they correlate with the outputs of each deep layer cell type; (4) the organization of local circuits that mediate computations in V2. These goals will be achieved by using a combination of anatomical and physiological methods in living in vitro brain slice preparations. Neurons in area V1 and V2 will be intracellularly labeled and their axonal and dendritic arbors reconstructed to determine their contributions to local cortical circuits. The V1 neurons will also be subject to EM analyses to identify ultrastructural properties of the synapses formed by the various cell types in this area. Scanning laser photo-stimulation will be used to reveal the source of local functional input to individual superficial and deep layer neurons in V1. Some of the superficial V1 neurons will previously have been retrogradely-labeled allowing identification of the extra-striate cortical areas that they target, while deep layer neurons with the various output patterns will be identified by intracellular labeling of their axonal arbors. These combined photo-stimulation and anatomical approaches therefore allow the identification of functional input sources to cells whose outputs are anatomically identified. These analyses reveal the flow of visual information across multiple synapses, allowing an unprecedented view of visual cortical circuits.
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