The long-term objectives of this study are to use electrophysiological and anatomical techniques to understand the neural control of vergence and ocular accommodation in primates. Whenever eye movements are made between objects located at different distances, changes in vergence and ocular accommodation are required. Deficits in either vergence or accommodation often result in common oculomotor complaints such as diplopia, blurred vision, headaches, and reading problems. These problems can result from either insufficient or excessive amounts of convergence, divergence, or accommodation. They can also result from an inability to appropriately adjust the gains of the adaptable elements that cross-couple the vergence and accommodative systems or an inability to appropriately adapt tonic levels of vergence and accommodation. In general, we know very little about the neural control of vergence and accommodative eye movements. In particular, we know essentially nothing about the neural mechanisms of their adaptive capabilities. Information of this nature should provide important insights into the underlying causes of deficiencies in vergence and accommodative eye movements. To address the issues raised above, the proposed experiments will be carried out in alert, behaving Rhesus monkeys. In general, we propose to investigate the role of specific cerebellar and precerebellar nuclei in controlling vergence and accommodative eye movements; we also propose to begin to identify the regions of the cerebral cortex that are involved in these eye movements. Specifically, we intend to use electrophysiological techniques to study single-unit activity in the cerebellum related to the sensory components of a far target. We propose to investigate how single- unit activity in specific cerebellar and precerebellar regions is influenced by phoria adaptation and by adaptation of the gains of the cross-links coupling vergence and accommodation. Then, to further examine the role that these regions play in these adaptive capabilities, we propose to study how reversible and permanent lesions of them affect the ability of the animal to show adaptation. We will also document any effects that these lesions have on the fast vergence and accommodation integrators. A region of the nucleus reticularis tegmenti pontis, a precerebellar nucleus, has been shown to play a role in vergence and accommodative eye movements. Anatomical studies indicate that this region receives a significant input from cells in the frontal eye fields (FEF). We therefore believe that cells related to vergence and accommodation may be located in, or near to, the FEF. Using microstimulation and single-unit recording, we propose to investigate the FEF and surrounding areas for vergence and accommodation regions. Finally, we propose to better characterize vergence and accommodation pathways in the primate by injecting anatomical tracers into physiologically-identified vergence and accommodation regions and studying the connections that are demonstrated.
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