Effects of transcranial magnetic stimulation over the region of the supplementary motor area during sequences of memory-guided saccades.

Transcranial magnetic stimulation (TMS) over the region of the supplementary motor area (SMA) was used to study the cortical control of sequences of memory-guided saccades. In ten healthy subjects, TMS was applied during (a) the target presentation (learning) phase, (b) the memorization phase, and (c) the execution phase of such saccade sequences. Stimulation during the presentation phase resulted in a significant increase in errors, compared to the results without stimulation. In contrast, stimulation during the memorization or execution phases had no significant influence on the performance of these sequences. The effect of TMS during the presentation phase seems to be specific for an interaction with the SMA function, since, in a control experiment with TMS of the occipital cortex during the same phase, the results were similar to those without stimulation. It is hypothesized that different cortical areas are involved in the learning, memorization and execution of sequences of memory-guided saccades. The SMA action could be crucial during the learning phase, but not during the memorization and execution phases of such sequences.