Presented in part at the 8th International Congress on Schizophrenia Research, Whistler, British Colombia, Canada, April 30, 2001. Received Jan. 17, 2001; revisions received June 26 and Aug. 17, 2001; accepted Aug. 29, 2001. From the Cognitive Neuropsychiatry Research and Academic Unit, Department of Psychiatry, and the Howard Florey Institute, University of Melbourne, Victoria, Australia; Sunshine Hospital, Melbourne; the Applied Schizophrenia Division, Mental Health Research Institute, Parkville, Victoria; the School of Psychological Sciences, La Trobe University, Bundoora, Victoria; the PET Centre, Austin and Repatriation Medical Centre, Heidelberg, Melbourne; and the Brain Sciences Institute, Swinburne University of Technology, Hawthorn, Australia. Address reprint requests to Dr. Yücel, Cognitive Neuropsychiatry Unit, Mental Health Research Institute, Locked Bag 11, Parkville, Victoria, Australia 3052; email@example.com (e-mail). Supported by a Ph.D. scholarship from La Trobe University (Dr. Yücel), a National Alliance for Research on Schizophrenia and Depression Young Investigator Award (Dr. Stuart), National Health and Medical Research Council (NHMRC) grant 970599, the NHMRC Brain Research Network, the Woods Family, and the Ian Potter Foundation. The authors thank Drs. Phyllis Chua, James Olver, and Simon Collinson for their assistance with task and subject preparation and image acquisition. They also thank the PET Centre staff for their assistance and support throughout the study.