A study of brain-evoked potential in 100 ms after transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS)-evoked N100 component (TMS-N100) is a negative peak wave at about 100 ms after TMS to the motor cortex. To elucidate the contribution of somatosensory and auditory inputs to the generation of TMS-N100, and to determine the cognitive effect of this potential, we recorded TMS-N100 with the TMS-compatible whole-head 60-channel EEG system from 10 healthy subjects. The peak latencies and pattern of potential distributions were similar between TMS-N100 under the ignore condition and the potential evoked by SMT+AUD in 100 ms (SMT+AUD N1) under the ignore condition. The amplitude of TMS-N100 significantly increased under the cognitive condition, while the latency and the potential distribution of TMS-N100 were not changed. These cognitive effects were also observed on SMT+AUD N1 under the cognitive condition. Therefore, inputs of TMS-N100 are the magnetic stimulation to the cerebral cortex and somatosensory and auditory inputs accompanied with TMS. The amplitude of TMS-N100 is increased by performing the cognitive task, thus, the cognitive status should be considered when the amplitude of TMS-N100 is interpreted.