Context- and experience-dependent modulation of the sensorimotor transformation for smooth pursuit eye movements

Smooth pursuit eye movements work in combination with other eye movement systems to ensure stable vision in a non-stationary world. Pursuit eye movements are tracking eye movements that allow primates to keep moving objects stable on the retina for improved visual processing. Although the basic task of the pursuit system is to perform a sensorimotor transformation that generates an eye velocity that matches target velocity, the relationship between target motion and subsequent eye movement is not fixed. This thesis investigates the neural signals that modulate the sensorimotor transformation for pursuit, based both on current context and on previous experience.; The amplitude of the pursuit response to a brief perturbation of target velocity is larger if the perturbation is presented during ongoing pursuit vs. during fixation. To understand the neural signals used by the pursuit system to control the gain of the response to target perturbations under different initial conditions and thereby constrain the possible sites and mechanisms of context-dependent pursuit modulation, I used passive whole body rotation to distinguish between eye velocity (eye in head) and gaze velocity (eye in world) signals. Adaptive modification of the vestibulo-ocular reflex allowed a further distinction between gaze velocity per se and the visually-driven component of gaze velocity. The results demonstrate that signals intermediate to gaze velocity and visually-driven gaze velocity control context-dependent modulation of pursuit.; In a separate set of experiments, I investigated the signals that modulate the sensorimotor transformation for pursuit based on experience. Specifically, I used microstimulation in cortical area MT to test the hypothesis that visual motion signals represented there could provide instructive signals for pursuit learning. The results demonstrate that activity in MT, consistently associated with pursuit in a given direction, is sufficient to drive learning for pursuit. Additional experiments stabilizing the target on the retina and using motion of a visual background to mimic MT stimulation demonstrate that visual signals in general, including target motion relative to the eye, and activity in MT, are provide powerful instructive signals for pursuit learning under physiological conditions.