Structural and Functional MRI: Scans will be acquired on a 3.0T GE magnet at baseline and upon 12-week follow-up at the Stanford Center for Cognitive and Neurobiological Imaging (CNI). Both structural and functional brain imaging will be conducted, and total scan time will be 1 hour. All scans will be examined by a neuroradiologist to detect the presence of unanticipated structural lesions, including tumors, infarcts, and other abnormalities or signs of vascular injury. Data from subjects with abnormalities will be excluded from further analysis and they will be contacted and referred for a clinical scan. We expect less than 10% of scans to be excluded on this basis.