Microstimulation of the supplementary eye field during saccade preparation

Electrical stimulation of the supplementary eye field (SEF) of monkeys has been reported to evoke saccades with low threshold currents. In previous reports, the evoked saccades have appeared either as 'converging', 'goal directed', or at times 'constant vector'. In the present study, a new aspect of intracortical microstimulation (ICMS) was found when the stimulus was applied at the time when an animal was prepared to initiate its own voluntary saccades. A cue signal was given to the animal that indicated targets of impending saccades. After a variable delay period, a 'go' signal told the monkey to initiate the saccade toward the target. ICMS was applied shortly (50-100 ms) before the go signal. The stimulus-evoked saccades were directed toward and captured the cued target, provided that the target direction was contralateral to the cortical stimulus site. Saccades with that property were evoked only from a limited portion of the cortical field that corresponded to the SEF, characterizing this particular oculomotor area.