Very low-frequency rTMS modulates SEPs over the contralateral hemisphere.

In order to investigate the transcallosal effects of repetitive transcranial magnetic stimulation (rTMS), we studied median somatosensory evoked potentials (SEPs) before and after applying monophasic very low-frequency (0.2 Hz) subthreshold rTMS over the right motor cortex. For SEPs, median nerve was stimulated on each side. Sham rTMS served as the control. Twelve healthy subjects participated in this study. After rTMS over the right hemisphere, the amplitude of N34 component in right median SEPs recorded from the left parietal scalp (C3') increased significantly. Other components of right or left median SEPs or those after sham stimulation showed no changes. Monophasic 0.2 Hz subthreshold rTMS over the motor cortex predominantly affected the contralateral SEPs, probably through the transcallosal pathway.