The purpose of this study is to clarify the role that the pontine nuclei and cerebellum play in the control of visually guided smooth motor behavior as exemplified by smooth-pursuit eye movements. Implicated within cerebellar vermal lobules VI and VII is a neural correlate of a target velocity signal of import to the smooth pursuit control system. We seek to determine the anatomical and physiological origins for the sensory and oculomotor signals that comprise the target velocity signal. Anatomical results implicate the dorsolateral pontie nucleus (DLPN) as a major mediator of sensory and oculomotor information. To elucidate the sensorimotor signal processing occurring in DLPN, signle unit recordings will be made of DLPN activity during the performance of selected visuo-oculomotor tasks. Of special, though not exclusive, concern will be retinal image slip-related neuronal activity that is relevant to oculomotor control. Vermal lobules VI and VII and the flocculus are involved with oculomotor behavior and receive inputs from DLPN. Utilizing both antidromic stimulation and extracellular recording techniques, we will determine the type(s) of sensorimotor information conveyed by DLPN to these two cerebellar regions. The results should help clarify whether these structures play parallel or independent roles in smooth-pursuit eye movement regulation. Furthermore, an investigation of smooth-pursuit eye movements in the absence of lobules VI and VII and the fastigial nucleus of the cerebellum will facilitate a re-examination of the clinical custom of attributing only saccadic dysmetria to vermal pathology. Clarification of the elusive functional significance of oculomotor proprioception will derive from correlating eye movement-related vermal Purkinje cell activities with proprioceptive responses Knowledge of the sensorimotor interactions occurring in dorsolateral pontine neurons and the cerebellar regions they project to, will shed light on the functional basis of tecto- and cortico-ponto-cerebellar pathways. An understanding of how the pursuit eye movement system processes sensory and motor information will facilitate clarification of the neural substrate for smooth-pursuit eye movement regulation.
