Primate gaze (line of sight in space) movements require coordinated interactions between visual, vestibular and oculomotor systems. The long-term goal of this study is to define the role of different components of the cortico-ponto-cerebellar system in gaze behavior. Our preliminary studies, employing multiple retrograde and anterograde tracers, indicate considerable specificity in anatomical connections between different regions of cortex and the basilar-pontine nuclei including the dorsolateral pontine nucleus (DLPN) and nucleus reticularis tegmenti pontis (NRTP). These pontine nuclei are thought to play a critical role in processing gaze-related signals from the frontal eye field (FEF) and medial superior temporal (MST) cortex and delivering these signals to different regions of the cerebellum (e.g., ventral paraflocculus and vermis). Our preliminary results support the suggestion that DLPN and rNRTP play differential roles in smooth pursuit and gaze movements. The FEF and MST cortical areas appear to have biased inputs to the NRTP and DLPN, respectively. These findings along with functional differences in response properties FEF, MST, NRTP and DLPN neurons support the suggestion that there could be separate gaze-related channels of information in the cortical-pontine system. Therefore, our studies are designed to compare and contrast gaze-related information carried in FEF-NRTP and MST-DLPN pathways in awake, behaving macaques. To accomplish this goal we will use quantitative methods (e.g., multiple linear -regression modeling) to define gaze-related signals (visual-, eye- and head-motion) carried in FEF, MST, DLPN and rNRTP neurons. We will include comparative analysis of gaze signals in different regions of FEF-NRTP and MST-DLPN pathways during gaze movements. Because only some cortical neurons project to the brainstem, we will use electrical stimulation of NRTP and DLPN to antidromically activate FEF and MST neurons. We will then be able to characterize gaze-related signals in these identified neurons. Our preliminary results indicate that neurons in the FEF-NRTP pathway provide information especially related to the initial phase of gaze movements. In contrast, neurons in the MST-DLPN pathway appear to provide signals related to maintaining gaze movements. Successful completion of our studies will provide new information that could help in the diagnosis and potential treatment of gaze disorders in patients.
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