SACCADIC EYE MOVEMENT STUDIES

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The ultimate goal of our work is to understand how the brain functions. To do this, we study the output ( motor) portions, using the oculomotor system as a model. Our recent studies of saccadic eye movements (the quick, step-like scanning eye movements we use to "look at" our visual world) have revealed new details about how saccades are programmed by the neural saccade generator. Specifically, we showed that the nucleus prepositus hypoglossi (nph) and the interstitial nucleus of Cajal cannot provide an internal control signal (local feedback) that specifies the correct saccade size. Thus, current models must be revised to account for our recent results and local feedback may not be used to control saccade amplitude as is commonly accepted in the oculomotor literature. Once the eye gets to its target, it must remain steady in order to provide clear vision. This is the job of the neural integrator, an hypothesized nucleus that converts velocity-coded commands into ey e-po sition discharge and thus integrates the signals in a mathematical sense. In another study, we confirmed that the nph, the putative location of the neural integrator, generates the oculomotor command signals to produce steady gaze at eccentric eye positions. However, it is apparently not used by the other oculomotor subsystems, such as the smooth pursuit or vestibulo-ocular systems, thus refuting the common integrator hypothesis. These results are basic to the differential neurological diagnosis based on eye movement signs now commonly used clinically as well as to our understanding of oculomotor processes. In addition, they provide a foundation for studies of more complex aspects of central nervous system function such as interactions between motor systems (e.g., eye and head during orientation) or sensory and motor systems (e.g., the visual and oculomotor systems) as well as more abstract functions such as attention and memory. FUNDING NIH grants RR00166 and EY06558. Kaneko, C. R. S. and Fukushima, K. Discharge characteristics of vestibular saccade neurons in alert monkeys. J. Neurophysiol. 79 835-847, 1998. Soetedjo, R., Kaneko, C. R. S., and Fuchs, A. F. The timing of SC activity does not support the moving hill model. Soc. Neurosci. Abstr. 24 418, 1998.