- Transcranial magnetic stimulation (TMS): For this test, a wire coil is held on the scalp. A brief electrical current passes through the coil to stimulate the brain. The stimulation may cause a twitch in muscles of the face, arm, or leg, and the subject may hear a click and feel a pulling sensation on the skin under the coil. During the stimulation, the subject is asked to: 1) perform the training task (make brisk thumb movements); 2) watch a video showing the hand of another person performing the same task; and 3) perform the task and watch the video at the same time, synchronizing his or her movements with those observed in the video.