Theta Burst Transcranial Magnetic Stimulation Can Modify Cortico-Muscular Coherence in Humans

Previous studies have shown that repetitive transcranial magnetic stimulation (rTMS) can modify cortical excitability in humans, and particularly that a recentlyproposed rTMS protocol, “theta burst stimulation” (TBS) can induce the long-lasting effects with the stimulation duration much shorter than those of conventional rTMS protocols. However, in those studies, the effects of rTMS were assessed mainly by means of motor evoked potential, and how the rTMS affects functional coupling between cortex and muscle was least studied. Here, we examined the coherence between electroencephalographic (EEG) and electromyographic (EMG) signals during isometric hand (first dorsal interosseous muscle) contraction, before and after application of TBS to primary motor area (PMA). Magnitude of the EEG-EMG coherence at beta band (13–30Hz), localizing for the C3 scalp site, significantly decreased 30–60 minutes after TBS and, in 90–120 minutes, gradually recovered to the control level before TBS. The present results suggested that TBS applied to PMA can suppress the cortico-muscular synchronization.