Fixation and saccade generation by the frontal eye field

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It has been well known that the frontal eye field (FEF) is responsible for generation of saccadic eye movements. Recently, it turns out that the FEF is also involved in generating smooth pursuit eye movement and convergence eye movement.In contrast, the present study was aimed at identifying the area in the FEF where electrical stimulation produced suppression of saccadic eye movements in the monkey. In addition, the properties of the suppression on saccades were investigated by changing various parameters for the electrical stimulation. For this purpose, the monkeys were trained in a conventional way to make visually-guided saccades to a visual target on the screen in front of them. Then, the FEF was systematically surveyed to find an area whose stimulation suppresses visually-guided saccades. Stimulus intensity for intracortical microstimulation was limited to less than 50 μA. In a fairly wide area of the classical FEF where stimulation produced saccades, stimulation with intensities … More sub threshold for saccade generation could suppress the saccades ipsilateral to the stimulation side, but not the saccades contralateral to it. In contrast, stimulation of the area adjacent to the classical FEF where no saccades were evoked at 100 μA, stimulation at less than 50 μA could easily suppress saccades in both ipsi- and contralateral directions. Stimulation of this site suppressed saccades in 8 directions covering all directions, and strengths of the suppression on the saccades in these different directions were almost equal. This suppression continued as the stimulus duration was increased. Thresholds for the suppression on saccades in ipsi- and contralateral directions were as low as 10 μA and almost equal. To examine the properties of neurons in this suppression area of the FEF, spikes were recorded during the fixation task. Neurons in this area showed increase of activities during the fixation even without a fixation target. These neurons stopped firing at the onset of saccades in any directions. Further properties of these neurons in response to the fixation task are now being investigated. Less