Background: Little is known about the time it takes for nerve signals to go from one area of the brain to another. Using advanced methods for brain research, researchers want to look at the time it takes to send messages between different brain areas. They also want to develop new tests. Objectives: To develop tests to measure the sizes of nerve fibers in the peripheral nerve system and in the brain. Also to find out the different speeds that information travels in nerve fibers. Eligibility: Healthy, right-handed people ages 18-70 Design: Participants will be screened with medical history and a physical exam. Participants will have up to 7 visits depending on the tests they choose. Visits last about 2-4 hours and may involve the following tests: * Physical exam * Urine tests * Magnetic resonance imaging (MRI). Participants lie on a table that slides into a scanner. They will be in the scanner for up to 1 hour. For some scans, sensors are placed on the skin. They will get earplugs for loud noises. * Small, sticky pads on the skin will electrically stimulate nerves in the forearm. * Transcranial magnetic stimulation (TMS). A wire coil will be held to the scalp. A brief electrical current passes through the coil to affect brain activity. * Electroencephalography. TMS will be given to the brain. Small electrodes on the scalp measure brain activity. Participants may do small tasks. * Electrodes on the scalp will send an electrical current to the brain. * A cone with magnetic detectors will be lowered onto the head to record brain activity. Participants will perform various tasks.
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measure motor evoked potential (MEP) amplitude
Timeframe: throughout