Cerebral Mechanism of Visually Guided Eye Movements

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We tried to reveal the role of the frontal eye field (FEF) in the generation of visually guided eye movements using alert macaque monkeys. We first localized the extent of the FEF as the cortical area in which intracortical microstimulation elicites saccadic eye movements. The area was found to be restricted in the anterior bank of the arcuate sulcus extending anteriorly to the cortical exposed surface. In thus defined FEF, there was topographic organization regarding the amplitude of the electrically elicited saccade. We obtained saccades with similar amplitude and direction in all depth of a cortical locus. When stimulating different loci, saccade vector properties changed systematically. A small saccade was elicited in the lateral portion of FEF, and a large one was in the medial portion. We also investigated the visual input to the FEF by recording visual neurons. They were diffusely present in the FEF, and they were again topographically organized. In the lateral portion, neurons had small receptive fields near the center of gaze. Neurons in the medial portion had large receptive fields in the peripheral visual field. Then, we further examined the relation between the visual input and the motor (saccadic) output in each locus. The saccade brought the visual line into a part where the visual receptive field had occupied before the stimulation, suggesting that the visual input facilitates the saccade generation. Considering these results together with differentiation in the afferent and efferent neural structures, we postulated that the FEF plays an important role in the generation of saccades triggered by a visual object.