 Participants also undergo transcranial magnetic stimulation TMS and electromyography EMG before, during and after these activities. For TMS, a wire coil is held on the scalp. A brief electrical current is passed through the coil, creating a magnetic pulse that stimulates the brain. The effect of TMS on the muscles is detected with small electrodes taped to the skin of the arms or legs. EMG measures the electrical activity of the muscles. For this test, small electrodes are taped to the skin over the muscle. 