The global working hypothesis is that corticopontine pathways that project to visual and visuomotor-related pontine structures are subcortical branches of the hierarchical schema conceptualized for vision-related cortical areas. The goal is to gain an understanding of pontine function in order to organize pontine structures into a conceptual framework. Roles in visuomotor signal processing have been implicated for the cortical areas projecting to the pontine nuclei of interest. Presumably a pontine functional hierarchy would process similar visuomotor signals in controlling visually guided behavior. The proposed studies will be conducted against a background of extensive progress in characterizing cerebral cortical mechanisms responsible for visuo-oculomotor signal processing. These cortical areas are known to project to the nucleus reticularis tegmenti pontis (NRTP) and several nuclei of the pontine grey, but knowledge of the function of these pre-cerebellar structures is limited. The proposed studies seek to provide this knowledge and broaden our understanding of parallel corticopontine roles in regulating visuo-oculomotor behavior. The specific goal of the proposed study is to clarify the role that selected pre-cerebellar nuclei play in the control of visually guided smooth motor behavior as exemplified by smooth-pursuit eye movements. Attention will be focused on (i) the visuo-oculomotor signal processing in NRTP and pontine grey terminal zones for parietal and frontal eye field projections, (ii) the effects upon ocular motor behavior of pharmacological lesions and microstimulation in NRTP and selected pontine nuclei, and (iii) clarifying the functional significance of enhanced visual responses in the dorsolateral pontine nucleus' In each of these studies, single unit responses will be recorded during the performance of a variety of visual motion- and visuo-oculomotor related tasks. A behavioral study will employ ibotenic acid as a pharmacological agent. The proposed investigations of visuo-oculomotor signal processing in NRTP and selected pontine nuclei will contribute to the long-term goal of (i) creating a conceptual framework to organize pontine structures and (ii) 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 should ultimately be of diagnostic value in the neuro-ophthalmic clinic. Our results will provide a better understanding of anatomic functional specificity that will aid the physician in identifying and treating neurologic diseases.
