Role of the prefrontal cortex in the control of express saccades. A transcranial magnetic stimulation study

Single pulse transcranial magnet stimulation (TMS) was applied in five subj ects during a saccadic gap task, i.e. with a temporal gap of 200 ms between the extinguishing of the central fixation point and the appearance of, the lateral target. In all subjects, a significant increase of contralateral e xpress saccades was found when TMS was applied over the dorsolateral prefro ntal cortex (DPFC) at the end of the gap of 200 ms. Earlier stimulation ove r the DPFC during the gay had no significant effect. Furthermore, stimulati on over the posterior parietal cortex with the same time intervals, and sti mulation during a no gap task had no significant influence on express sacca des. These results suggest that TMS is capable of interfering specifically with the functioning of the DPFC, probably by inhibition of this region. Po ssibly such stimulation of the DPFC reduces the inhibition by this region o nto the superior colliculus, which results in a facilitation of express sac cades. (C) 1999 Elsevier Science Ltd. All rights reserved.