The long term goal of the proposed research is to describe forebrain mechanisms involved in the initiation and visual guidance of eye movements and in the selective fixation of targets. Previous unit recording studies, performed in monkeys trained to orient their gaze and to fixate visual targets, have shown that a region of the central thalamus, centered on the intralaminar nuclei, contain neurons related to spontaneous and evoked saccades, as well as neurons responding to visual stimuli. The objective of the proposed unit recording and microstimulation studies in trained monkeys is to elucidate the functional significance of the thalamic signals observed. This will be attempted by: a) testing specific hypotheses about the role of these signals in the control of the gaze. b) determining (by antidromic stimulation) at least some of the cortical areas to which specific signals are transmitted. c) comparing these signals when a gaze shift is accomplished by the eyes alone or by coordinated head and eye movements. The clinical significance of studies aiming at uncovering the role played by the central thalamus in the control of the gaze is attested by recent reports of the effects of central thalamus lesions in man. These lesions were shown to produce unilateral neglect, abnormal roving eye movements and hypometric saccades.
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