Role of neural variation in smooth pursuit eye movements

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Smooth pursuit eye movements are a well-understood behavior with a known neural substrate. Pursuit is generated when a target moves smoothly. It depends on a traditional cortical-cerebellar circuit with inputs from sensory cortex, processing in parietal sensory-motor areas, and motor commands from a frontal motor area. Outputs from the cerebral cortex interact with cerebro-cerebellar circuits and cerebro-basal ganglia circuits to generate motor commands. Much is known about the mean responses of neurons in these areas and how they contribute to the generation of the average pursuit movement. However, the analysis of variation in neural codes and pursuit behavior opens a new vista. The sensory input for pursuit is highly variable, yet the behavior itself is remarkably precise. The presence and ease of quantifying variation in the neural signals and the behavior offers the opportunity to ask where neural variation falls on the continuum from being a negative, neutral, or positive component of the neural generation of behavior. This project will focus on the frontal pursuit area (FPA), near the saccadic frontal eye fields and will ask 3 questions that are tightly linked to the aims of the Conte Center for Neuroscience Research. First, it will ask how much the neural code in the FPA varies and what fractions of the variance are 1) related to the behavior and 2) "residual", unrelated to the behavior. How do these fractions vary over the different phases of a pursuit movement? Second, it will use differential reward and penalty to modulate the distribution of behavioral variation and explore how that variation is effected by changes in the neural variation in the FPA. Third, it will explore neural variation in the FPA during the instructional period for visually-guided learning in pursuit, and during the subsequent expression of learning. The research in this project will contribute to the overall goals of the CCNR by providing an exemplar behavior where narrowly defined, quantitative questions can be answered about the specific roles of neural variation in a tightly controlled and well-understood behavior. In addition, an understanding of how the frontal cortex controls pursuit may help us to understand why schizophrenics have such profound deficits in smooth pursuit eye movements.