For the current protocol, participants have three 2-hour testing sessions at the NIH Clinical Center, scheduled at least one day apart. In each session, sponge electrodes are placed on the head so that they affect different areas of the brain. Two areas are involved with hand movement; the third does not. The electrodes are dampened with water and attached to the sides of the patient's head. When the current is turned on, the patient may feel some tingling. The current is on for 40 minutes, but can be reduced or stopped early if the tingling becomes uncomfortable.