Physiological, Cognitive and Cerebral Activity Changes as a Function of Cigarette Smoking (With or Without Nicotine) and Tobacco Abstinence

Background: * Denicotinized cigarettes are similar to commercial cigarettes but contain and deliver virtually no nicotine. Denicotinized cigarettes are used as a control condition in smoking research, as a substitute treatment for nicotine dependence, and as a strategy to reduce incidence of nicotine addiction. However, the symptoms of nicotine withdrawal and craving for cigarettes must be minimized to ensure that smokers will continue to use denicotinized cigarettes instead of their preferred cigarettes. * Although research has shown that smokers preferred cigarettes that delivered nicotine, subjective measures of tobacco craving and withdrawal were similar after standard and denicotinized cigarettes. This suggests that the process of smoking and non-nicotine components of tobacco smoke mediate some of the effects of cigarette smoking. More research is needed on the comparative physical and mental effects of regular cigarettes and denicotinized cigarettes. Objectives: \- To compare the effects of complete abstinence or smoking denicotinized cigarettes with smoking nicotinized cigarettes on the following measures: (1) withdrawal symptoms and quality of sleep, (2) hormonal responses, (3) mood and cognitive performance, and (4) functional brain activity. Eligibility: \- Men between 18 and 50 years of age who are either current smokers (at least 15 cigarettes per day for at least 2 years) or nonsmoking volunteers. Design: * Participants will be divided into four groups: (1) nonsmokers, (2) smokers who receive nicotinized cigarettes, (3) smokers who receive denicotinized cigarettes, and (4) smokers who will abstain from cigarettes. * The study will last 16 days. Smokers will have 14 visits to the clinical center; nonsmokers will have 6 visits. From Day 6 to Day 14, current smokers will follow the smoking regimen assigned by the researchers (not smoking, smoking denicotinized cigarettes, or smoking nicotinized cigarettes). * Nonsmokers will have one day of trainin