Crossed inhibition of sensory cortex by 0.3 Hz transcranial magnetic stimulation of motor cortex.

Low-frequency repetitive transcranial magnetic stimulation (rTMS) of motor cortex causes persistent inhibitory effects in the targeted area. rTMS of motor cortex impairs sensory perception and results in a persistent change in cortical function at remote sites. The ability of rTMS to induce sustained changes in cortical function has led to studies testing its therapeutic efficacy in neurologic disorders, including epilepsy. Studies on the effect of low-frequency rTMS of motor cortex on the contralateral motor cortex have provided evidence for both inhibitory and excitatory changes. This study was designed to determine the effect of low-frequency rTMS of the right motor cortex on the contralateral sensory cortex. Before and after 0.3-Hz rTMS of right motor cortex, perception of ipsilateral threshold of cutaneous stimuli was assessed and somatosensory evoked potentials (SEPs) recorded after stimulation of the right thumb in eight normal subjects. In a control group of six subjects, sensory responses were assessed after rTMS anterior to the right motor cortex. After rTMS of motor cortex, detection of threshold sensory stimuli decreased by more than 50% compared with pre-rTMS (P < 0.05). The change in sensory perception lasted at least 30 minutes. No change was detected in the control group. Amplitude of the N20-P25 waveform of the SEP decreased from a mean of 0.84 muV before rTMS to 0.54 muV immediately after rTMS of motor cortex (P < 0.05). 0.3 Hz rTMS of motor cortex inhibits the contralateral sensory cortex.