Neural Control of Visually Guided Eye Movements

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DESCRIPTION (provided by applicant): The aim of the proposed research is to determine how three cortical areas in the primate contribute to the generation of visually guided saccadic eye movements: the frontal eye fields, the medial eye fields and the lateral intraparietal sulcus. The experiments we propose are designed to assess: (1) How the signals from the cortex reach the brainstem oculomotor centers, (2) how excitatory and inhibitory circuits in these three areas mediate eye-movement control, and (3) the extent to which the three areas are also involved in eye/hand coordination. Three sets of experiments are planned: Experiment 1 will determine whether in the intact animal saccadic eye-movement generation is achieved through two parallel channels, the anterior and the posterior, as we had hypothesized in our earlier long-term lesion studies. To determine whether these two pathways are functional in the intact animal, the effects of electrical stimulation of the frontal eye fields and medial eye fields will be studied using short-term unilateral and bilateral reversible inactivation of the superior colliculus. Experiment 2 will assess the role excitatory and inhibitory neuronal circuits play in the frontal eye fields, the medial eye fields and the lateral intraparietal sulcus in eye movement control. To accomplish this, the generation of eye movements will be studied in a series of behavioral tasks when these areas are infused with briefly acting agonists and antagonists of glutamate and GABA. Experiment 3 will determine the extent to which these three areas contribute to eye/hand coordination in addition to saccadic eye-movement generation. Performance on eye/hand coordination tasks will be assessed before, during and after local infusions of reversible blocking agents. The results obtained from the proposed experiments should have significant implications for the treatment of eye-movement disorders. If in the intact organism the anterior and posterior streams, as had been proposed in our earlier work, are indeed functional, as to be determined in the first set of experiments in this series, more effective treatment routines can be devised than if all cortical commands to move the eyes traverse through the superior colliculus.