The effects of microstimulation of the dorsomedial frontal cortex on saccade latency.

Neural regions in the dorsomedial frontal cortex (DMFC), including the supplementary eye field (SEF) and the presupplementary motor area (pre-SMA), are likely candidates for generating top-down control of saccade target selection. To investigate this, we applied electrical microstimulation to these structures while saccades were being planned to visual targets. Stimulation administered to superficial and lateral DMFC sites that were within or close to the SEF delayed ipsilateral and facilitated contralateral saccades. Facilitation was limited to saccades made toward targets in a narrow, contralateral movement field that had endpoints consistent with the goal of evoked saccades. Facilitation occurred with current delivered before target onset and delay with current applied after this time. Stimulation at deeper, medial sites that encompassed the pre-SMA resulted in mostly bilateral delay. The amount of delay at these sites was usually greater for ipsilateral saccades and increased with current amplitude. Changes in saccade latency were not accompanied by altered endpoint, trajectory, or peak velocity. The spatial specificity of SEF stimulation in inducing latency changes suggests that the SEF participates in selecting saccade goals. The less specific delay with pre-SMA stimulation suggests that it is involved in postponing visually guided saccades, thus likely permitting other oculomotor structures to select saccade goals.