Transcranial Magnetic Stimulation (TMS) is a non-invasive technique that can be used to stimulate brain activity and gather information about brain function. It is very useful when studying the areas of the brain and spinal cord related to motor activity (motor cortex and corticospinal tract). Repetitive transcranial magnetic stimulation (rTMS) involves the placement of coil of wire (electromagnet) on the patient's scalp and rapidly turning on and off the electrical current. The changing magnetic field produces weak electrical currents in the brain near the coil. This permits non-invasive, relatively localized stimulation of the surface of the brain (cerebral cortex). The effect of magnetic stimulation varies, depending upon the location, intensity and frequency of the magnetic pulses.