This study will be conducted in three phases. In Phase 1, participants will be admitted to the Clinical Center while continuing to take their medication and will undergo diagnostic interviews, physical and laboratory assessments, physiological monitoring, and neuropsychological testing. Behavioral ratings will also be performed and blood and urine samples will be collected. During Phase 2, participants will continue taking medications in a blinded fashion for 8 to 12 weeks. The active medications will be replaced with a placebo (an inactive pill) part of that time. PET, fMRI, and MRI scans will be used to monitor how the continuation or lack of medication affects the brain. Psychological tests will also be given to measure changes in cognition. In Phase 3, participants will have the opportunity for clinical stabilization.