Repetitive Transcranial Magnetic Stimulation Equipment Testing and Pilot Study

Background: \- Brain stimulation called repetitive transcranial magnetic stimulation (rTMS) may help people quit drugs. Researchers want to study how it works in healthy people first. Objective: \- To learn how to use rTMS to stimulate a brain area and to see how it affects brain function and thinking. Eligibility: \- Healthy, right-handed adults ages 18-55. Design: * Participants will be screened under another protocol. * They will have 4-11 study visits. * To start each visit, participants will have: * Physical exam. * Urine sample. * Breath tests for alcohol and cigarette smoke. * Questions about drug use and medications. * Visit 1: participants will have: * Single TMS pulses on the head to determine the right strength. They will wear earplugs and a cap. A wire coil will be placed on the head and an electrical current will go through it. Participants may perform simple muscle movements. They will repeat the procedures wearing another coil, in a helmet. * A few TMS pulses to show how rTMS feels. * A practice thinking task, maybe in a scanner that looks and sounds like a magnetic resonance imaging (MRI) scanner but does not take pictures. The MRI scanner is a metal cylinder surrounded by a strong magnetic field. The participant will lie on a table that slides in and out of the cylinder. * They may have a real MRI scan. * Visits 2-11, participants will: * Complete two questionnaires. * Get varied rTMS stimulation. Their heart rate and blood pressure may be monitored. * Have their vital signs checked. * They may perform thinking tasks at a computer, in a mock scanner, or in an MRI scanner. They may just lie still in the MRI scanner.