Topographic Organization of Saccade-Related Response Field Properties in the Marmoset Posterior Parietal Cortex.

Despite various histological, electrophysiological, and imaging studies, the topographic organization of saccade-related activity in the posterior parietal cortex (PPC) has been notoriously difficult to characterize. In part, this is because areas of interest in PPC are often embedded deep in sulci in macaques and humans. Understanding the extent of topographic organization in PPC can provide insights into the computation contributions of PPC. The lissencephalic cortex of the common marmoset offers a unique opportunity to investigate fine-scale topographic organization in PPC. Recordings were obtained from the PPC of two male marmosets performing a visually guided center-out saccade task with 8 or 36 peripheral targets using multichannel electrode arrays with 100 μm spacing. By plotting the pattern of saccade direction tuning preferences across all penetrations and cortical depths, we uncovered topographic organizational features within the PPC. Like other primates, multiunits in marmoset PPC tend to prefer saccade targets in the contralateral visual field. The results detail how preference for saccadic direction changes in a systematic manner across cortical distance, such that response units closer in proximity tend to show systematic changes in their tuning preferences. Across cortical distance, the visual field was also systematically encoded but reversals in direction varied across penetrations. The analysis highlights the likelihood of multiple representations of the visual field for saccade direction preference across PPC. These novel findings suggest a possible functional organization of saccade-related activity in marmoset PPC, giving insights into the computational capacity of the PPC.