The goal is to clarify the role that pontine and cerebellar nuclei play in the control of visually guided smooth motor behavior as exemplified by smooth eye and/or head movements. Attention will be focused on (i) investigating interactive, sensori-oculomotor mechanisms in the dorsolateral pontine nucleus and the fastigial nucleus of the monkey and (ii) clarifying cerebellar roles in regulating corrdinated eye and head movements. Anatomical results implicate the dorsolateral pontine nucleus (DLPN) as a major mediator of sensory and oculomotor information. To elucidate the sensorimotor signal processing occurring in DLPN, single unit recordings will be made of DLPN activity during the performance of selected visuo-oculomotor tasks. Of special, though not exclusive, concern will be interactive, direction-selective visual and visuo-oculomotor mechanisms that are relevant to the regulation of smooth-pursuit eye movements. Single unit responses to various combination of relative target and background motion will be investigated with the goal of clarifying the neural mechanisms underlying DLPN involvement in tracking targets against a visual background. In addition, the neuronal activity associated with the different stages of the initiation of smooth-pursuit eye movements will be studied together with the effects of micro-stimulation on eye movements at each stage of initiation. The goal will be to clarify the neural mechanisms involved with the initiation of pursuit. Extracellular activity will be recorded in the fastigial nucleus in order to test the hypothesis that a neural correlate of target velocity in space exists in this intracerebellar nucleus and that this singal contributes to fastigial roles in smooth-pursuit control and in coordinating eye and head movements. The investigations of sensorimotor mechanisms in DLPN and festigial nucleus will contribute providing a comprehensive functional picture of cerebro-ponto-cerebellar roles in regulating visually guided motor behavior. The determination of the neural substrates for the regulation of smooth-pursuit eye movements and the coordination of eye and head tracking should ultimately be of diagnostic value in the clinic.