The visual system requires a stable image for optimal performance. The optokinetic system works in consort with the vestibular ocular reflex to maintain visual image quality during locomotion. In addition, the visual system is served by saccadic and smooth pursuit eye movement systems in foveating either stationary or moving targets, respectively. Our research is directed at studying the neural basis of some of these important eye movement systems. The overall objective of the proposed research is to study the formation of commands for eye movements that occurs in brainstem regions specifically related to smooth eye movements. We will pursue this research by using several different approaches centered around studies in the trained rhesus monkey. Our own studies as well as those of others have demonstrated that the nucleus of the optic tract (NOT) and dorsolateral pontine nucleus (DLPN) play important roles in optokinetic and smooth pursuit eye movements. Using the potent GABA agonist, muscimol, we will unilaterally inactivate the NOT to assess its potential role in the short latency ocular following response and in the initiation of smooth pursuit. To further our understanding of these visually elicited eye movements, we will study the transformation of cortical signals that occurs in the NOT and DLPN to produce smooth eye movements. The response properties of brainstem and cortical units will be tested during smooth pursuit, optokinetic, ocular following and saccadic eye movements, as well as during visual stimulation. Eye movements will be measured with the scleral search coil technique. Electrical stimulation, delivered in the NOT and DLPN, will be used to antidromically activate identified MT and MST units. This will allow us to determine the properties of cortical neurons projecting to the NOT and DLPN. Discrete permanent lesions will be placed in the NOT and DLPN to determine their relative contribution to the ocular following response, optokinetic nystagmus and to the initiation and maintenance of smooth pursuit. Finally, we will perform correlative anatomical studies to further elucidate the anatomical substrate of the visual/oculomotor pathways responsible for smooth eve movements. The results obtained in these studies will advance our understanding of the visual and oculomotor systems. These findings will assist in diagnosis and potential treatment of disorders effecting vision and the oculomotor system.
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