B. Patients (either male or female) will range in age from 18 to 65 years. Female patients of child-bearing potential will have a pregnancy test prior to each PET and MRI scan and specific interview prior to the study to ensure that pregnant patients will not participate in the study. Patients will be asked to stop for two weeks prior to the exam any medication that can influence the CNS. Fluoxetine will be stopped for four weeks. They will be asked to abstain from alcohol for one week before the study.