Modulation of mu wave by repetitive transcranial magnetic stimulation and transcranial direct current stimulation to the motor cortex

rTMS (repetitive transcranial magnetic stimula- tion) is a method which stimulus cerebral nerve by induced current in the brain. It is possible to inhibit or facilitate neu- ronal activity in the brain. tDCS (transcranial direct current stimulation) can also modulate cortical activity just as rTMS. tDCS is a method which stimulate the brain with the direct current generated at electrodes attached on the subject's scalp. Depending on the current polarity, duration or strength, tDCS can induce after effects selectively. Mu wave is traditionally defined as an 8-12Hz wave recorded over sensorimotor cortex that decreases or desynchronizes with imagination of move- ment. However the rTMS and tDCS effects to the mu wave are still unclear. The aim of this study is to investigate the effects of rTMS and tDCS on mu wave. Electroencephalograms (EEGs) were measured before and after the stimulation of rTMS or tDCS. 1Hz rTMS, Anodal tDCS and Cathodal tDCS were applied over the motor hand area of the thumb. On the measurement of EEGs, subjects were required to do motor imagery of grasping right hand when the indication of the word "Imagery" was displayed on the monitor. Electromyography (EMG) was measured simultaneously to remove the data of moving hand during the motor imagery. The peak frequency bands around 10Hz of each subjects were used and the amount of power difference at the frequency bands of mu wave with motor imagery, rTMS and tDCS were calculated and compared. It was found that the power of mu wave tend to decrease with anodal tDCS. In contrast, 1Hz rTMS and cathodal tDCS tend to increase that EEG power. Although rTMS and tDCS can modulate that EEG power, the amount of difference with rTMS and tDCS is smaller than that of difference with motor imagery.