Subjects brain waves are recorded using magnetoencephalography (MEG) while they are experiencing tics andpre-tic sensory experiences. MEG is a test that records magnetic field changes produced by brain activity. Subjects sit in a chair under a dome containing magnetic field detectors. They watch a clock and report the time a sensory experience starts. Tics are recorded with EMG. Later, a standard MRI of the brain (scan using a magnetic field and radio waves) is done to see which parts of the brain produced the activity recorded with MEG.