Contributions of the Lateral Intraparietal Cortical Area to Smooth Pursuit Eye Movements

We use the information we receive through our senses to guide our movements. Our daily lives are full of far more sensations than we want to act upon, however, so it is essential that our brain can direct the right parts of our sensory experience to our motor systems. This thesis explores how the brain might control how strongly a visual input affects action in the context of smooth pursuit and saccades, which are the eye movements we use to keep a moving object in our high-resolution center of vision. I explored the hypothesis that area LIP is involved in the control of smooth pursuit by recording from the area while monkeys followed moving targets. I found that the trial-to-trial fluctuations of LIP firing rate and pursuit velocity were correlated. This "LIP-pursuit correlation" was present for pursuit both before and after the saccade. The correlation with postsaccadic pursuit velocity could not be explained away when metrics of the saccade were included as control variables. The LIP-pursuit correlation was not present when the target appeared outside the receptive field of the neuron under study. Variability in the strength of the LIP-pursuit correlation was predictable from the from the average firing rates at the end of the saccade. Meanwhile, one monkey performed another task in which the target did not move. In this task, there were nonetheless small postsaccadic eye movements known as "glissades", and LIP activity was also correlated with these glissades. Taken together, these results suggest that LIP is involved in the guidance of pursuit eye movements. I conclude by discussing what sort of role LIP could be playing in the pursuit system, and speculate that it could be either encoding features of the motion such as direction or speed or it could be setting a gain that determines how strongly visual motion at a spatial location is converted to an eye movement