Participants will undergo prepulse inhibition tests to assess nervous system function. The participant sits comfortably in a quiet room. Several cables are attached to the face and legs using a special cream that conducts electrical signals through the cables to recording equipment. Nervous system activity is evaluated while the subject is at rest and after sensory stimulation (stimulating the nerves in the legs and face with a very brief electrical current of mild to moderate intensity). At times, the subject receives a short, mild sound stimulation delivered through earphones. The testing session takes 4 to 6 hours.