Objective. Chronic nicotine exposure is thought to lead to alterations in the dopamine (DA) system that leaves smokers in a hypo-dopaminergic state during periods of abstinence. Varenicline (Chantix), a new efficacious smoking cessation medication, is thought to lead to a modest but sustained increase of DA release thereby reducing nicotine craving and withdrawal. While numerous studies have shown that varenicline is a safe, well-tolerated, and effective pharmacological treatment for nicotine dependence, studies exploring the neurophysiological impact of this drug in the human brain have not been conducted. This protocol will utilize an array of reward processing and cognitive control tasks to explore the effects of subtle DA manipulations (induced by smoking cessation, transdermal nicotine, and varenicline) on brain function and behavioral performance. Brain function will be assessed using functional magnetic resonance imaging (fMRI) and electroencephalography (EEG).