Effect of repetitive transcranial magnetic stimulation on saccades in depression: a pilot study

Therapeutic repetitive transcranial magnetic stimulation (rTMS) in depression is applied over the prefrontal cortex. This brain region is known to play an important role in the control of saccades. We wanted to investigate whether the fast rTMS procedure affected saccadic activity in depression. Reflexive saccades (RS) and voluntary saccades were studied in 11 patients before and after therapeutic rTMS for depression. Two types of voluntary saccade tasks were used: a voluntary prosaccade (VpS) task and an antisaccade (AS) task. Eye movements were registered by infrared oculography. Latency and directional error rate were analyzed. rTMS was applied over the left dorsolateral prefrontal cortex (DLPFC). RS and VpS parameters were unchanged after 10 sessions of rTMS. However, the latency of antisaccades (AS) was significantly shorter after rTMS than before rTMS. It can be concluded that rTMS over the left DLPFC cortex in depression seems to have no important effect on reflexive saccades, while antisaccade activity is clearly favored by shortening of latency. As voluntary prosaccades were not significantly influenced, our findings may indicate that not merely the voluntary triggering of saccades but the inhibition of unwanted reflexive saccades is influenced by fast rTMS delivered over the DLPFC. These results suggest the intriguing possibility that rTMS might differentially affect specific aspects of saccade behavior.