This project will explore the role of the cerebellar flocculus in the directional organization of the vestibulo-ocular reflex in cats. We will measure the eye movements of the vestibulo-ocular reflex in the presence and absence of flocculus influence, and we will record the neural activity of flocculus neurons and the brainstem neurons that receive flocculus signals. The results will tell us whether or not the flocculus is necessary for aiming vestibulo-ocular reflex eye movements, and the extent to which adaptation of the direction of vestibulo-ocular reflex eye movements depends on the flocculus. (1) We will record the amplitude and direction of vestibulo-ocular reflex eye movements during rotations in many directions and in many body orientations. Vestibulo-ocular reflex will be recorded before, during, and after procedures which elicit adaptive changes in reflex direction. These recordings will be repeated in cats that have received bilateral lesions of the flocculus. In other cats, the flocculus will be reversibly inactivated by infusion of lidocaine or other agents. This inactivation will be done either before, during, or after vestibulo-ocular reflex direction adaptation, to test the role of flocculus in normal reflex and in establishing and retaining adaptive state. (2) We will record single neuron activity from flocculus purkinje neurons before, during, and after vestibulo-ocular reflex adaptation procedures. We will record the activity of brainstem vestibular neurons, including those that receive flocculus input, under the same conditions. The changes in complex spikes and simple spikes of flocculus purkinje cells across these conditions, and the changes in brainstem neuron responses, will allow us to reject or support hypotheses about the site and nature of learning processes that involve the cerebellum.
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