TRANSCRANIAL MAGNETIC STIMULATION SELECTIVELY IMPAIRS INTERHEMISPHERIC-TRANSFER OF VISUO-MOTOR INFORMATION IN HUMANS

We investigated the cerebral cortical route by which visual informatio n reaches motor cortex when visual signals are used for manual respons es. Subjects responded unimanually to photic stimuli delivered to the hemifield ipsilateral or contralateral to the moving hand. On some tri als, trans-cranial magnetic stimulation (TMS) was applied unilaterally over the occiput, with the aim of stimulating extrastriate visual are as and thereby modifying transmission of visual input. In association with the side of a visual stimulus and a motor response, TMS could cha nge inter-or intra-hemispheric transmission needed to convey visual in formation to motor areas. Reaction time differences following TMS sugg ested that TMS exerted an inhibitory effect only when visuo-motor info rmation had to be transferred interhemispherically. This result reinfo rces evidence for an extrastriate pathway of interhemispheric transfer of visuomotor information.