rTMS over human motor cortex can modulate tremor during movement

Abnormally large tremor during movement is a symptom of many movement disorders and significantly impairs activities of daily living. The aim of this study was to investigate whether repetitive magnetic brain stimulation (rTMS) can reduce tremor size during human movement. We hypothesised that inhibitory rTMS over motor cortex would reduce tremor size during subsequent movement. The study involved 26 healthy young adults (21 ± 2 years) and began with application of single TMS stimuli to measure baseline corticospinal excitability. The response to stimulation was recorded in hand muscles with electromyography. Subjects then performed a 3-min task to measure baseline tremor during movement. This involved matching index finger position with a moving target on a computer screen. Tremor was recorded with an accelerometer on the fingernail. Finger acceleration was analysed with fast-Fourier transform to quantify tremor in the physiological range (7.8-12.2 Hz). Subjects then received 10 min of real (n = 13) or sham (n = 13) inhibitory rTMS. Tremor and corticospinal excitability were then remeasured. Real rTMS significantly decreased corticospinal excitability by ~30% (P = 0.022) and increased tremor size during movement by ~120% (P = 0.047) relative to sham rTMS. However, the direction of tremor change was opposite to that hypothesised for inhibitory rTMS. The results suggest that rTMS over human motor cortex can modulate action tremor and the level of corticospinal excitability may be important for setting the amplitude of action tremor in healthy young adults.