3. The investigators will use TMS to test motor cortex functions. For these tests, participants will sit in a chair that looks like the one at the dentist's office. A magnetic coil will be placed on the scalp on one side of the head, overlying the brain's motor cortex to stimulate the brain's output to the muscles in the opposite hand. A second magnetic coil will be placed on the scalp of opposite side. Recordings from both hands will be made using the magnetic coils placed on scalp.