Participants will undergo a medical history and physical examination. During the study, they may have three or four sessions of MRI. During the MRI, patients will lie still on a table that can slide in and out of a metal cylinder surrounded by a strong magnetic field. Scanning time varies from 20 minutes to 3 hours, with most scans lasting between 45 and 90 minutes. Patients may be asked to lie still for up to 60 minutes at a time. As the scanner takes pictures, there will be loud knocking noises, and the patients will wear earplugs to muffle the sound. Patients will be able to communicate with the MRI staff at all times during the scan and may ask to be moved out of the machine at any time. Some scans may be done in a 3 Tesla scanner. It is the latest advance in MRI, with a stronger magnetic field than in the more common 1.5 Tesla scanner. Functional MRI (fMRI) is done while patients are performing tasks, such as moving a limb or speaking. Patients will have an opportunity to practice such tasks before entering the scanner. The fMRI will take about 1 hour.