 For the TMS procedure, subjects are seated in a comfortable chair with their hands placed on a pillow on their lap. An insulated wire coil is placed on the scalp. A brief electrical current is passed through the coil, creating a magnetic pulse that stimulates the outer part of the brain, called the cortex. This may cause muscle, hand or arm twitching if the coil is near the part of the brain that controls movement, or it may affect movements or reflexes. Subjects are asked to make movements, do simple tasks, or tense muscles. Metal electrodes are taped to the skin over the muscle for computer recording of the electrical activity of the hand and arm muscles activated by the stimulation. The testing lasts 2-3 hours. 