REVERSIBLE INACTIVATION OF MACAQUE FRONTAL EYE FIELD

The macaque frontal eye field (FEF) is involved in the generation of s accadic eye movements and fixations. To better understand the role of the FEF, we reversibly inactivated a portion of it while a monkey made saccades and fixations in response to visual stimuli. Lidocaine was i nfused into a FEF and neural inactivation was monitored with a nearby microelectrode. We used two saccadic tasks. In the delay task, a targe t was presented and then extinguished, but the monkey was not allowed to make a saccade to its location until a cue to move was given. In th e step task, the monkey was allowed to look at a target as soon as it appeared. During FEF inactivation, monkeys were severely impaired at m aking saccades to locations of extinguished contralateral targets in t he delay task. They were similarly impaired at making saccades to loca tions of contralateral targets in the step task if the target was flas hed for less than or equal to 100 ms, such that it was gone before the saccade was initiated. Deficits included increases in saccadic latenc y, increases in saccadic error, and increases in the frequency of tria ls in which a saccade was not made. We varied the initial fixation loc ation and found that the impairment specifically affected contraversiv e saccades rather than affecting all saccades made into head-centered contralateral space. Monkeys were impaired only slightly at making sac cades to contralateral targets in the step task if the target duration was 1000 ms, such that the target was present during the saccade: lat ency increased, but increases in saccadic error were mild and increase s in the frequency of trials in which a saccade was not made were insi gnificant. During FEF inactivation there usually was a direct correlat ion between the latency and the error of saccades made in response to contralateral targets. In the delay task, FEF inactivation increased t he frequency of making premature saccades to ipsilateral targets. FEF inactivation had inconsistent and mild effects on saccadic peak veloci ty. FEF inactivation caused impairments in the ability to fixate light s steadily in contralateral space. FEF inactivation always caused an i psiversive deviation of the eyes in darkness. In summary, our results suggest that the FEF plays major roles in (1) generating contraversive saccades to locations of extinguished or flashed targets, (2) maintai ning contralateral fixations, and (3) suppressing inappropriate ipsive rsive saccades.