After numbing the skin or muscles of the arm or leg where a pre-tic sensation is experienced, the response of the nerves will be tested by asking subjects to rate the strength of the sensation after a pinprick and by stimulating the nerves with small electrical shocks. Then, over the course of approximately one hour, subjects will report pre-tic sensations while their motor tics are counted. The onset of each tic will be identified with EMG, a test using electrodes on the skin to indicate the activity of the muscles.