Changes of resting-state EEG microstates induced by low-frequency repetitive transcranial magnetic stimulation

Repetitive Transcranial magnetic stimulation (rTMS) is a noninvasive brain stimulation technique that can influence cortical excitability. Low-frequency rTMS (stimulation frequency <= 1Hz) induces long-lasting inhibitory effects on cortical excitability. At the same time, EEG microstates have been studied and have been thought to corresponding to functional relevant brain-states. In order to investigate dynamic changes in EEG microstates after low-frequency rTMS, 20 healthy subjects received 1-Hz rTMS over the right motor area, and electroencephalography (EEG) in resting condition with eyes open was recorded before rTMS (Pre) and at 0 min, 20 min, 40 min, and 60 min after rTMS (Post0, Post20, Post40, and Post60). Resting state EEG data of all five sessions were computed using a clustering algorithm. Four EEG microstates were found and labeled with the letters A, B, C and D. No significant difference in duration was found among five sessions for four microstates. For microstates A, and B, there is an increase in the mean duration immediately after rTMS. And for microstate C, the mean duration at Post0 and Post60 was significantly higher than that before rTMS. For microstate D, there is an increase in the mean duration at 60min after rTMS. These results showed that we reproduced the same four microstate maps best representing the resting state EEG as found by others and that low-frequency rTMS produced long-lasting alterations in the mean duration of EEG microstates. It implies that low-frequency rTMS increases the stability of EEG microstates.