Abstract
The objective of the present study was to determine whether methadone maintenance treatment (MMT) in heroin-dependent patients affects inhibitory control, whether any MMT-induced changes correlate with methadone dose and MMT duration, and whether these changes depend on the psychological characteristics of patients, such as depression, anxiety and impulsivity. Response inhibition in the GO/NO-GO test was combined with functional magnetic resonance imaging (fMRI) scanning data to examine whether MMT affects inhibitory control in 21 heroin-addicted patients who had already undergone at least three months of MMT. Patients were evaluated one year prior to and after the MMT period. Participants exhibited no difference in their GO/NO-GO reaction time and accuracy rate, or in their false alarm rate under NO-GO conditions. However, increased activation was detected in numerous brain regions in their 12-month fMRI scans, although these were not in the frontal-striatal loop. Increased fMRI activation in the left precentral gyrus and superior temporal gyrus were negatively correlated with the daily methadone dose and total methadone dose during the one-year study period. In conclusion, these results suggested that MMT over one year does not significantly change the behavioral indicators of inhibitory control function in heroin-dependent patients. The increase in activation leads to the hypothesis that MMT over one year may increase cognitive inhibitory control, which may be the result of the combined negative effect of methadone and the positive effect of functional recovery after withdrawal of heroin.