A subject will be excluded if he/she has a contraindication to MRI scanning such as the following: Aneurysm clip; Implanted neural stimulator; Implanted cardiac pacemaker or autodefibrillator; Cochlear implant; Ocular foreign body or implant (e.g. metal savings, retinal clips); breast implants; or Insulin pumps. Subjects will be excluded if they have claustrophobia. A pregnancy test will be administered to women of childbearing age. Pregnant women will be excluded from the studies.