 Before the TMS session, participants undergo magnetic resonance imaging MRI to determine where to place the coil for TMS. For MRI, the subject lies still for up to 30 minutes at a time on a table that slides into the scanner, a narrow metal cylinder surrounded by a strong magnetic field. Earplugs are worn to muffle loud knocking sounds that occur while the scanner takes pictures. Subjects can communicate with the MRI staff at all times and can ask to stop the procedure at any time. 