Smokers participated in the following 2 imaging sessions: after 24 hours of biochemically confirmed abstinence (carbon monoxide level, <10 ppm) and after smoking as usual (last cigarette about 20 minutes before the scan). Sessions were performed 1 to 3 weeks apart in counterbalanced order. Participants refrained from use of alcohol or other drugs for at least 24 hours before sessions, confirmed by results of a urine drug screen and a breath test for alcohol. Severity of nicotine dependence was assessed by the Fagerström Test for Nicotine Dependence (FTND).25 The Minnesota Nicotine Withdrawal Scale,26 the brief Questionnaire on Smoking Urges (QSU),27 and the Positive and Negative Affect Schedule28 were administered before each scan. Subjects underwent a 5-minute high-resolution anatomical scan, a 6-minute resting scan, and a 15-minute visual N-back WM task.8 Unless otherwise specified, data are expressed as mean (SD).
