Transcranial magnetic stimulation of extrastriate cortex degrades human motion direction discrimination.

The human temporo-parieto-occipital junction is an extrastriate visual area that may mediate motion vision processing. We determined if transcranial magnetic stimulation (TMS) delivered over this extrastriate area would degrade motion discrimination, similar to the transient decrease in spatial acuity observed when TMS is delivered over striate cortex. TMS was delivered 50-250 msec after the onset of a brief, random dot, motion direction discrimination task or a spatial acuity task. TMS significantly reduced correct motion discrimination when delivered 100-150 msec after the random dot stimulus. During the same time window TMS did not significantly effect spatial acuity. TMS over the left extrastriate cortex reduced motion discrimination in both hemifields and its effect had a crude topographical organization. TMS safely perturbs extrastriate visual areas and may reveal the temporal sequence of higher perceptual processing.