Design: This is a natural history study in which subjects will have a series of neurophysiological tests. Transcranial magnetic stimulation (TMS) is a non-invasive technique that allows for measures of cortical excitation and inhibition. Electroencephalography (EEG) measures baseline brain electrical activity. Nerve conduction studies measure the speed of conduction of impulses by peripheral nerves. Polysomnography records sleep cycles and associated eye movements, muscle potentials, heart rate, and respiration.