Participants will be asked not to sleep the entire night before the test. Before the scan, both patients and volunteers will have EEG electrodes placed on their heads to record the electrical activity of their brains. Patients will also have EMG electrodes placed in areas of the body where tics occur. A small catheter (plastic tube) will be placed in an arm vein for injecting the radioactive tracers, and a mask will be placed on the face to help keep the head still during scanning. The mask has large openings for eyes, nose and mouth, so that it does not interfere with talking or breathing. The entire test takes about 4 hours. During this time, the subject will sleep for 1.5 hours either at the beginning or end of the scan. For the other 2.5 hours, scans will be done every 10 minutes for 1 minute under the different conditions of tic suppression or release of tics.