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, a single neuron recording was used to probe the mechanisms whereby the frontal eye field of the monkey achives spatial accuracy. It is well known that frontal neurons respond to stimuli in a certain location int he retina, the receptive field. The receptive fields of frontal 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. Frontal neurons also demonstrate a memory mechanism: they respond to flashed targets well after the stimulus has left the receptive field. Such neurons also respond to recently flashed targets whose spatial location will be brought into their receptive fields by a saccadic eye movement. These neurons provide insight into the mechanism by which the oculomotor system can perform in a spatially accurate manner despite the constant motion of the eyes. In the second inquiry, the oculomotor performance of normal rhesus monkeys was used to probe the processing that underlies saccadic eye movement. Monkeys were trained to perform express saccades, very short-latency eye movements that occur when there is no current attentive fixation. They were then trained on short-term saccadic adaptation, a motor learning task designed to study the plasticity of motor behavior in the monkey. Monkeys trained on a normal adaptation task had adapted express saccades; monkeys trained on express adaptation also had adapted normal saccades. In the third inquiry, eye movements were used to follow the clinical status of patients with Type 3 Gaucher's disease who were receiving enzyme replacement therapy. Although their liver size and general status improved with treatment, their oculomotor performance failed to improve.