Individual Differences in Reward and Impulse Control

Background: \- The risk for becoming addicted to drugs varies among individual, even those using similar drugs in a similar way. It is not known why some people become addicted and others do not. Studies suggest that some genes may increase the risk of addiction. Negative life experiences may also affect the risk of addiction. Researchers want to test smokers and nonsmokers to study genetic and brain function traits that may lead to drug addiction. Objectives: \- To understand brain function in people who may be at a higher risk of drug addiction. Eligibility: * Healthy volunteers between 18 and 55 years of age. * Smokers (10 to 30 cigarettes per day for more than 2 years) and nonsmokers will be eligible. Design: * Participants will be screened with a physical exam and medical history. They will be tested for drug and alcohol use. A blood sample will be collected. * The study will involve one visit. Participants will have a magnetic resonance imaging (MRI) scan. * At the visit, participants will answer questions about their health and drug use habits. They will then be trained on the tasks they will do during the MRI scan. After the training, they will have the scan and perform the tasks. The scan and tasks will look at brain function related to rewards and impulsiveness. * Other computer tests will be given after the scan. These tests will measure learning, memory, and impulsiveness.