Alpha-generation as basic response-signature to transcranial magnetic stimulation (TMS) targeting the human resting motor cortex: A TMS/EEG co-registration study

The effects of repetitive transcranial magnetic stimulation (rTMS) on cortical excitability are usually inferred from indirect indexes, such as EMG responses. It has now become possible to directly evaluate rTMS impact by means of concurrent EEG recording. The aim of this study was to examine the modulation induced by high frequency rTMS (20 Hz) over left primary motor cortex on the ongoing oscillatory activity. Thirteen subjects underwent two sham and a real rTMS session while acquiring EEG. Event-related desynchronization/synchronization was calculated for the a and beta bands. rTMS induced a dose-dependent increase in synchronization in both bands over central and parietal sites. The strongest effect found for the a band outlasted the end of the stimulation. Considering previous studies, our data suggest that a generation may represent an intrinsic induced response and a basic response signature to TMS targeting the human resting motor cortex.