Participants will undergo diffusion tensor MRI, MR-spectroscopy, and magnetization transfer imaging to look at different compositional, architectural, and microscopic properties of the brain. All of these techniques are similar to conventional MRI, and like the conventional method they use a strong magnetic field and radio waves to measure structural and chemical changes in brain tissue. Each of the three scans will be done on separate days, each lasting about 1 hour. For the procedures, the patient or volunteer lies on a stretcher in a narrow metal cylinder (the scanner) and is asked to remain still for 15 to 30 minutes at a time. A special lightweight coil may be placed on the head to enhance the brain images. The subject can communicate with the person doing the scan at all times.