Recent studies have demonstrated that electrical stimulation delivered over the skin increases the muscle strength as measured by a dynamometer in chronic stroke patients. We recently also found out that such stimulation enhances the ability of healthy brains to learn faster, enhancing the beneficial effects of the motor training.

The purpose of this study is to find out if this stimulation can enhance the ability of stroke patients to experience plastic changes in the brain. It may aid in the development of new strategies for rehabilitation after brain injury in the future.

A clinical and neurological exam will be administered. Each patient will participate in three different sessions separated by at least 48 hours: a 2-hour peripheral nerve stimulation to the weak hand, a 2-hour peripheral nerve stimulation to the leg, and no stimulation. The sessions will be randomly ordered. A magnetic resonance imaging scan of the brain will be done as well.

Nerve stimulation will be done by transcranial magnetic stimulation (TMS). In TMS, the head is immobilized within a frame. An insulated coil wire is placed on the scalp and brief electrical current passed through it. Participants may be asked to perform movements, do simple tasks, or simply tense muscles. Electrical activity of the muscles will be recorded with a computer. Some experiments may be recorded on videotape.

Participants must be stroke patients who have recovered to the point of being able to make thumb movements, and the stroke must have occurred more than 6 months ago.