This study will analyze a series of biological and behavioral markers in different populations of smokers. The study groups will differ in their cigarette consumption and level of nicotine dependence. This analysis will help to identify factors that might be important for smoking behavior and nicotine addiction. The results from this study will contribute to improve campaigns for smoking prevention and treatments for smoking cessation.

Inclusion Criteria:

• healthy adults
• age 25-55

Exclusion Criteria:

• alcohol or drug addiction
• unstable significant medical problems
• neurologic disease
• medications known to affect CNS function or impact physiologic parameters measured in the study
• significant visual impairment
• breath carbon monoxide (BCO) level of less than 10 ppm for smokers
• breath carbon monoxide (BCO) level of more than 5 ppm for non-smokers
• for heavy regular smokers: erratic smoking history (i.e. they must have smoked an average of 15 cigarettes daily for at least one year)

General population