ORGANIZATION OF INFEROTEMPORAL CORTEX

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DESCRIPTION: (from the investigator's abstract) The long term goal of this research is to elucidate the mechanisms of object perception in the primate visual cortex. In the current proposal, anatomical and physiological techniques will be used to analyze the modular organization of cortical areas V2 and V4 in macaque monkeys and to determine the connections of these modules with area V1 and with inferotemporal cortex. The first goal is to determine the specific patterns of connections of individual V2 cytochrome oxidase (CO) thin stripe and interstripe compartments with area V4. Optical recording of intrinsic cortical signals will be used to identify V2 compartments, in vivo. V2 thin stripes will be identified by their relative activation by iso- luminant color stimuli, while inter-stripes and thick-stripes will be identified by their orientation selectivity and disparity selectivity. Tracer injections targeted at adjacent thin and inter-stripe compartments of V2 will compare their patterns of terminations in V4 and will confirm the nature of their inputs from V1. Injections of distinguishable tracers into functionally distinct portions of the same stripe will reveal their specific connections with modules in V1 and V4. Functional heterogeneity in thin stripes may be due to the segregation of color information from brightness or other surface properties such as texture. Injections into these submodules will test whether these functionally distinct cell clusters project to segregated foci in V4. In complementary experiments, injections into separate orientation- specific clusters in V2 interstripes will test whether V2 projects to V4 in an orientation-specific manner. The second goal is to determine the functional architecture of V4 and to determine the connections of functionally defined clusters in V4 with V2 and inferotemporal cortex (IT). First, optical recording will be used to identify V2 compartments, in vivo. Then, optical recording of V4 will be combined with microstimulation of individual V2 thin stripe and interstripes to identify the terminal domains of these V2 compartments in area V4. Second, optical recording in V4 will be combined with visual stimulation to identify cell clusters that are preferentially activated by chromatic, luminance, orientation, dynamic texture, or motion stimuli. Distinguishable anterograde and retrograde tracers will be injected into these V4 compartments to identify the distribution of their terminals in V2 and inferotemporal cortex. These experiments test whether the V4 modules that analyze object borders or those that analyze the surface properties of color, brightness and texture, project to segregated loci in IT. The third goal is to determine he organization of the intrinsic circuits within areas V2 and V4. The same distinguishable anterograde tracers used in the study of the extrinsic connections of V2 and V4 will reveal the local circuits that will be correlated with the cytochrome oxidase pattern in V2 and the functional maps in V2 and V4. These experiments test the degree of "cross-talk" between compartments that might provide the basis for the generation of more complex receptive field properties in these areas. Overall, these experiments will provide new insights into the mechanisms of integrated object perception in the visual cortex.