Participants will perform a sequential finger tapping movement in response to a series of numbers (stimuli) displayed on a computer monitor. After 10 stimuli, they will be asked which finger they tapped last. They will then imagine the same finger tapping movement and will be asked which finger they tapped last in their imagination. During these exercises, participants will undergo transcranial magnetic stimulation. For this procedure, the subject is seated comfortably in a chair. A wire coil is placed on the scalp and a brief electrical current is passed through the coil, creating a magnetic pulse that passes into the brain. This generates a very small electrical current in the brain, which briefly disrupts the function of the brain cells in the stimulated area. The stimulation may cause twitching in arm or leg muscles. During the stimulation, the electrical activity of muscles is recorded with a computer or other recording device, using electrodes attached to the skin with tape.