Changing cortical excitability with low-frequency transcranial magnetic stimulation can induce sustained disruption...

Transcranial magnetic stimulation (TMS) is promising as a therapeutic tool, and TMS of the motor system has served as a model for regionally specific modulations of cortical excitability. It is unclear, however, to what extent response characteristics of the motor cortex are representative of other brain systems. We wanted to determine whether TMS could induce a sustained disruption of somatosensory processing beyond the stimulation duration, similar to observations in the motor system. We applied 1-Hz TMS at 110% of subjects' motor thresholds for a variable duration over the right and left somatosensory cortex before subjects performed a tactile frequency discrimination task with the left hand. Tactile discrimination was impaired only after TMS over the right somatosensory cortex (analysis of variance: p <.01). The duration of this impairment correlated with the duration of the preceding TMS; the effect lasted approximately 2 min after 5 min of TMS, 4 min after 10 min of TMS, and 8 min after 20 min of TMS. Two conclusions arise: 1) low-frequency TMS can interfere with tactile perception in a robust and sustained way, and 2) TMS dosing parameters effective in the motor system are also effective in the somatosensory system and may reflect a modality-independent response characteristic of the cerebral cortex.