EEG modification induced by repetitive transcranial magnetic stimulation.

Repetitive transcranial magnetic stimulation (rTMS) is a powerful, noninvasive tool for investigating cortical physiologic functions in the brain. However, EEG spectral analysis has not been investigated extensively in rTMS study. The authors investigated the influence of rTMS on the EEG power spectrum by stimulating the left frontal cortex in 32 healthy subjects. Stimulation parameters were a 10-Hz frequency, a 3-second duration, and a 100% motor threshold. The data showed that rTMS increased the peak frequency of EEG across the scalp within 2 minutes after stimulation, whereas the value decreased at 3 to 4 minutes. The mean absolute powers within 3 minutes after rTMS did not differ from those estimated before rTMS, but increased uniformly at 4 to 5 minutes. The spectra did not change after sham stimulation. These results indicate that rTMS can influence cortical activities significantly by increasing the frequency and amplitude of EEG, and is a useful tool for helping us understand brain functions.