Tom P. Franken, M.D./Ph.D. - US grants

Project Summary/Abstract Making sense of visual scenes requires a correct assignment of the borders that occur between object and background, or between objects, to the foreground object. Macaque visual cortical areas V2, V4 and V1 contain neurons that are selective for border ownership. These cells encode border ownership even if distal visual cues that define which sides of a boundary are object and ground fall far outside of the neuron?s receptive field. This selectivity often persists even when these distal cues disappear, a form of stimulus hysteresis or memory. Prior studies suggest that this border ownership selectivity relies on corticocortical feedback from hypothetical downstream neurons with receptive fields that cover the complete object, termed grouping cells. No prior study has found these hypothesized grouping cells. Thus, though border ownership cells have been found, the neural circuits that endow them with border ownership selectivity remain poorly understood, as does their role in perception. The goals of the proposed research are to determine the micro-organization of border ownership and grouping cells in the macaque visual cortex, and to relate their activity to perceived border ownership. The candidate will use advanced electrophysiological, optophysiological and viral targeting techniques in behaving macaques to achieve these goals. In Aim 1, the candidate will use two-photon calcium imaging to identify border ownership cells and grouping cells, and test specific hypotheses about how they are organized within the columnar layout of macaque Area V4. In Aim 2, the candidate will combine two-photon calcium imaging and viral targeting techniques to distinguish excitatory from inhibitory neurons in V4, and assess their role in border ownership. In Aim 3, the candidate will relate the activity of border ownership and grouping cells in areas V2/V1 and V4 to perception by recording their activity with laminar multielectrodes while reading out perceived border ownership. The candidate has extensive electrophysiological expertise including in behaving non-human primates, but needs training in two-photon calcium imaging and viral approaches, which are the technical goals of the career development plan. The primary mentor is Dr. John Reynolds, a leader in the neurophysiology of visual cortex in behaving macaques. The co-mentor is Dr. Ed Callaway, a pioneer in viral targeting and two- photon imaging in macaques. Both Dr. Reynolds and Dr. Callaway have a strong history of mentoring young scientists and are faculty at the Salk Institute for Biological Studies, an institute with a strong history in visual neuroscience. Recent advances in optical recording techniques and viral approaches have enabled high- resolution studies of genetically targeted neurons in functioning neural circuits. Combined with his background in electrophysiology, the additional training will provide the candidate with the expertise that will enable him to launch a successful career as an independent investigator studying the neural basis of visual perception in behaving non-human primates. A deeper understanding of the computations performed in the primate visual cortex is imperative for designing better diagnostic tools and treatments for central visual processing disorders.