Psychology of Reward and Punishment: Functional and Molecular Brain Imaging and Monoaminergic Correlates

Background: * Brain imaging studies, genetic research, and investigations of stress have provided more information about the role of dopamine in processing reward and punishment, and in vulnerability to substance dependence. Researchers are interested in learning more about how the brain responds to rewards, including drugs of abuse, and how these responses may involve genetic factors or previous stressful events. * Researchers intend to use the drug amphetamine to increase levels of dopamine in the brain and study the effects through two kinds of scanning: functional magnetic resonance imaging (fMRI) and positron emission tomography (PET). Objectives: * To examine the relationship among dopamine function, brain activity, reward processing, genetic profile and exposure to stress in normal healthy adults. * To examine the variation in these factors between normal healthy adults and individuals with current cocaine-dependence. Eligibility: \- Individuals 18 to 45 years of age who are either current cocaine users or healthy volunteers with no history of substance abuse or dependence. Design: * The study will consist of an initial evaluation session and six study visits, four of which will involve fMRI scans (3 hours each) and two of which will involve PET scans (8 to 9 hours each). * Cocaine-using participants will enter the inpatient clinical research ward at the National Institute on Drug Abuse Addiction Research Center the night before each scanning session and will be discharged the following day. Healthy volunteer subjects will not be required to stay overnight and will arrive as outpatients for the PET session. Participants will not be released until researchers have determined that participants are not experiencing significant effects of the drug. * Initial session (1): Participants will complete questionnaires about past reactions to stressful situations, and will be trained to do thinking tasks that will be performed in fMRI visits. The tasks will be pr