The perception of a visual """"""""figure"""""""" often relies upon the overall spatial arrangement of its local elements, as demonstrated by the perception of occluded or illusory contours. The global attributes of a visual stimulus can affect the response of visual cortical neurons to the local attributes of the stimulus. For example, the response of neurons in cortical areas V1 and V2 to stimuli within their classical receptive field (cRF) can be modulated by contextual stimuli outside their cRF (in their """"""""surround""""""""). Similarly, V1 and V2 neurons respond to illusory contours (ICs) within their cRF. Neuronal cRFs and local interactions cannot account for these perceptual and neurophysiological phenomena; rather, fast interactions across distant visual field locations are needed to mediate perceptual completion. The long-term goal of this proposal is to disentangle the relative contributions of long-range inter-areal (feedforward and feedback) and intra-areal (horizontal) corticocortical connections to these global-to-local computations in early visual cortex. The neural circuitry and mechanisms involved are likely to be the cornerstone of contour integration, and figure-ground segregation. Thus, results from these studies ultimately will help understanding the neural substrates for higher visual cortical processing and perception in primate and man. ? As a first step towards the broader goal, the work described in this application is designed to investigate how the spatial extent and organization of intra-areal (Aim 1) and inter-areal, feedforward and feedback (Aims 2 and 3), connections relates to the spatial scale and organization of single V1 and V2 neurons' RF, modulatory surround field and response to ICs. The rationale is that the spatial scale of a given connectional system must be commensurate with the spatial scale of the specific neuronal response that it underlies in retinotopically-organized early visual cortex. We will map the total field of connections labeled by small tracer injected cortical points, and overlay these anatomical maps to physiologically recorded retinotopic maps from the same regions of cortex. The visuotopic scale of the connectional fields will then be related to the spatial dimensions of receptive field and modulatory surround field, and with the limits of neuronal responses to ICs, measured physiologically at the injected cortical points ? ?
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