People between 18 and 65 years of age with TS who have at least once tic involving an arm may be eligible for this 3-part study. Those enrolled may participate in all parts or in part 1 or part 2. Those who choose to participate in part 3 must first complete part 2. All must stop taking medication for TS and any other medication that may affect the brain for at least 1 week before the study.