CONTROL OF VERGENCE EYE MOVEMENTS BY THE FRONTAL CORTEX

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Alert, rhesus monkeys will be trained to perform oculomotor tasks to clarify how neurons within the prearcuate cortex (8Ar) encode the visual characteristics of binocular stimuli that elicit vergence eye movements. Visually-guided vergence eye movements are reported to be composed of an initial transient vergence component and a later, sustained fusional component that "locks" vergence angle sufficiently for sensory fusion to occur. These components have been studied extensively in humans but not in the rhesus monkey. Initially, these components of vergence eye movements will be characterized in monkeys using the electromagnetic search coil method. Subsequently, these vergence components and the sensory stimuli eliciting them will be correlated with single-unit activity recorded from neurons within the prearcuate cortex. I. The first aim will characterize the behavior of neurons within the prearcuate cortex during the transient and sustained components of vergence. Briefly presented dichoptic images or long presentations of dissimilar images will separate transient vergence from sustained vergence. II. The second aim will look more closely at those visual characteristics encoded by neurons within the prearcuate cortex. A forced-choice paradigm will be used to determine what target characteristics (e.g. luminance, orientation, spatial frequency) affect transient vergence and neural activity. III. The final aim uses dichoptic stimuli that dissociate binocular matches based on local and global cues during transient vergence. Correlated, dynamic random-dot stereograms will test how prearcuate neurons respond to these global disparity cues. The results of this project will improve our understanding of neurological deficits associated with strabismus and of vergence dysfunction.