Subjects were included in the study if they were (1) able to understand and give informed consent; and (2) had at least 12 years of education (or equivalent) and verbal intelligence ≥85 (estimated with the Wide Range Achievement Test reading subtest standard score). Subjects were excluded if they had: (3) history of head trauma or loss of consciousness (greater than 30 minutes) or other neurological disease of central origin (including seizures); (4) abnormal vital signs at time of screening or history of major medical conditions that may alter cerebral function, such as cardiovascular (including high blood pressure), endocrinological (including metabolic), oncological or autoimmune diseases for which the participant is required to take medications; (5) present or past history of psychiatric disorders other than substance abuse in cocaine abusers and nicotine dependence in all subjects; (6) positive urine screens for psychoactive drugs (or metabolites) other than cocaine (phencyclidine, benzodiazepines, cannabis, opiates, barbiturates and inhalants); (7) pregnancy, as confirmed with a urine test in all female subjects of childbearing age on study day; and (8) metal implants or other contraindications for MRI.
