CEREBRAL CORTICAL MECHANISMS FOR EYE MOVEMENTS AND VISUAL ATTENTION

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Three lines of inquiry were followed to determine how the cerebral cortex and its efferent regions control eye movements and visuospatial attention. In the first single, a neuron recording was used to probe the mechanisms whereby the parietal cortex of the monkey achieves spatial accuracy. It is well known that parietal neurons respond to stimuli in a certain location o the retina, the receptive field. The receptive fields of parietal neurons transiently change before a saccadic eye movement, so that they respond, before the eye movement, to stimuli that will be in their receptive fields after the movement. At the same time, the current retinal location becomes unresponsive. These data establish that there is a specific shift of retina receptive field, rather than a general change of excitability. In the second, the oculomotor performance of rhesus monkeys was assessed while the monkeys performed an oculomotor task before and after electrolytic lesions of the deep cerebellar nuclei. A number of deficits we found that were consistent with the cerebellum playing a role in adjusting the amplitude of saccadic eye movements but not in initiating them: monkeys had increased variability in the amplitude of their saccadic eye movements, they had tended to overshoot targets and this inaccuracy was dependent upon the initial position of the eye in the orbit; they were unable to adju the amplitude of their saccadic eye movements for target motion; and they could not adjust the amplitude of their saccadic eye movements in a model of muscle weakness. In the third, the performance of humans with superior cerebellar peduncle lesions was studied in a smooth pursuit task. Cross-coupling between the torsional and vertical pursuit systems was demonstrated.