Effects of Transcranial Magnetic Stimulation (TMS) on Somatosensory Perception

Background: \- Different parts of the brain are involved in feeling touch. Researchers want to study whether repetitive magnetic stimulation (rTMS) to the sensory cortex affects how sensation feels. rTMS is a repeated magnetic pulse that interferes with brain activity. It affects a small part of the brain beneath the scalp. Researchers want to find out the role of sensory cortex in sensing different types of touch. Objectives: \- To find out the role of sensory cortex, a brain area, in sensing different types of touch. Eligibility: \- Healthy adults ages 18 45. Design: * Participants will be pre-screened with a telephone interview. Then they will be screened with physical and psychological exams and a urine test. * In Session 1, participants will have an MRI brain scan and fill out questionnaires. * For MRI, a magnetic field and radio waves take pictures of the brain. Participants will lie on a table that slides in and out of a metal cylinder. A coil will be placed over their head. They will perform a task during the scan. The scanner makes loud knocking noises. Participants will get earplugs. They will be in the scanner for up to 60 minutes. * In Sessions 2 and 3, participants will take urine tests. Their perception of touch will be measured. Then rTMS will be used to stimulate their sensory cortex and scalp for about 20 minutes. Their perception of touch will be measured again. * For rTMS, a wire coil is held on the scalp. A brief electrical current passes through the coil and creates a magnetic pulse that affects activity in the brain.