Neuronal encoding of rapid categorical decisions across primate oculomotor networks

Project Summary In a professional table tennis rally, the time between successive ping pong ball hits is around 400ms. Within this timeframe, the players must rapidly categorize the motion and spin of the ball to appropriately guide the ongoing motion of their paddle to successfully strike the ball. While numerous studies have investigated the oculomotor system’s role in the visual categorization process, few have done so where the response must be initiated in advance of relevant sensory information, such as in the aforementioned example. Thus, the temporal dynamics of sensory modulation of saccadic decisions remain largely unresolved. To identify the manner in which visual categorization informs ongoing motor plans, I propose recording neural activity from populations of neurons in the lateral intraparietal area (LIP), frontal eye field (FEF), and superior colliculus (SC) while monkeys perform a saccade-based motion categorization task in which motor planning always precedes the identification of the visual stimulus; consequently revealing the temporal evolution of a categorical judgment with millisecond resolution. Results from prior studies identified neurons in LIP and FEF that demonstrate categorical tuning, with increased firing rates when stimuli belonging to the preferred category appear on screen. Additionally, a recent study from our lab demonstrates the causal role of LIP in visual categorization in which reversible inactivation of LIP leads to significant deficits in categorization accuracy. However, the task structure utilized by these studies precludes any attempt to uncover the manner in which categorical signals influence ongoing motor plans, or identify differences in the timing and strength of categorical encoding between these brain regions. To date, no study has investigated categorical encoding in SC, thus we will be the first to identify its role in visual categorization. By simultaneously recording from large, diverse populations of neurons with linear arrays across these interconnected brain regions, the proposed research will provide critical insight into the temporal dynamics underlying the transformation of sensory evidence into oculomotor decisions.