<qa>  What is the magnetic pulse that stimulates the brain?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 brain. This may cause muscle, hand or arm twitching if the coil is near the part of the brain that controls movement, or it may induce twitches or transient tingling in the forearm, head or face muscles. Subjects will be asked to move a finger. Just before this movement, a brief electrical stimulation will be applied to the end of either the second or fifth finger. Metal electrodes will be 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 will last 2-3 hours. 