Twenty seven right-handed male volunteers, including 14 chronic heroin users (HU, heroin using (from the time of their initial heroin use until the time of scanning) for 7.11 ± 2.82 years, range from 2 to 10 years) and 13 non-addicted controls (CN), participated in this study. All HU were recruited from Anhui Detoxification and Rehabilitation Center (Hefei, Anhui province, China), sought medical help on their own initiative and had a DSM-IV diagnosis of heroin dependence or abuse and urine tests positive for heroin before enrolling in the treatment program. According to an interview conducted by a clinical psychologist, all of the patients had never used any other types of illicit drugs, were free of illnesses that required hospitalization or regular monitoring and were deemed to be stable and able to participate in the experiment. Before the fMRI scanning, except 2 of HU who were current heroin users and not under any treatment, the HU were under a methadone treatment and had no illicit drug use during the treatment as confirmed by their care takers. Among the 12 HU under the
