Cortical areas are generally assumed to be uniform in internal structure, with each area homogeneously repeating a common processing module across its microcolumns. However, various lines of evidence indicate significant heterogeneities within individual areas of sensory cortex. Within primary visual cortex (V1), for example, the horizontal dimension of cortex is tiled with ocular dominance columns, orientation columns, and columns related to other stimulus attributes such as direction selectivity and spatial frequency. How the specific structure of any of these columns influences visual information processing is unknown. We propose to examine the effect of one set of columns -- orientation columns -- on cortical responses within V1. Our hypothesis is that the particular structure of the orientation map, comprised of pinwheel centers and orientation domains, regulates key features of neuron responses, of plasticity in these responses, and of vision. Specific questions are as follows: 1. Do neurons in iso-orientation domains and pinwheel centers of the orientation map in V1 integrate cortical inputs differently? 2. Does orientation selectivity of single neurons evolve with different time courses and dynamics at different locations within the orientation map? 3. Does the correlated firing of neuron pairs vary at different locations in the cortex? 4. Does short-term plasticity of orientation tuning, as revealed by briefly adapting V1 neurons to a particular stimulus orientation (""""""""temporal context""""""""), depend on cortical location? Does the degree of orientation plasticity relate to the size of orientation domains in which neurons are located? 5. What is the relationship between multiple V1 columnar systems such as those for space, orientation, direction, spatial frequency and ocular dominance? In particular, how does the proximity to pinwheel centers and iso-orientation domains influence the mapping of visual space? 6. Are long-range inputs that convey surround responses (""""""""spatial context"""""""") to neurons from outside their classical receptive field integrated differently at different locations in cortex? 7. Does V1 in alert monkeys show differences between pinwheel centers and iso-orientation domains with respect to: (a) the dynamics of orientation tuning at different map locations, (b) the effects of short-term pattern adaptation on orientation selectivity and dynamics, and (c) the effect of long-range inputs on response magnitude, selectivity and time course. 8. What is the effect of spatial attention on orientation-specific responses in alert monkey V1? 9. Does a related top-down influence, reward expectancy, modulate orientation-specific responses in alert monkey V1? Are these effects more pronounced at pinwheel centers, which integrate inputs broadly and might be particularly sensitive to signals that modulate response levels or gain? These experiments will utilize multiple approaches, including optical imaging of intrinsic signals, intracellular recording in vivo and extracellular unit recording with single and multiple electrodes to analyze how particular locations of V1 integrate local, long-range and descending inputs in space and time and hence provide the substrate for vision. The results would provide information that is fundamental for understanding cortical networks and function, and for treating malfunction and disease.
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