Study Summary

Using functional magnetic resonance imaging (fMRI) and three groups of subjects (a group of healthy subjects and two groups of male opiate dependent subjects on current methadone treatment.

The aim of the study is to:

1. Investigate whether abnormal reward prediction error signals are associated to opiate dependence. If such an abnormality is found, potentially it might help to explain drug seeking behaviour/craving in patients.
2. To investigate the neural substrates of reward discounting in opiate addicts. This is important as impulsivity is a prominent feature of some subjects with addiction and might help explain their increased vulnerability to developing the syndrome over time (Redish et al 2008).
3. To study the effect of methadone administration on reward prediction error signals and neural substrates of reward discounting, on opiate addicts under methadone maintenance treatment. Acute Methadone might act to increase phasic dopamine signals, or it might increase the background tonic dopamine level instead. There are theoretical arguments to support both but only a study can determine the effects. It is important to know which occurs, as this has direct effects on the putative mechanism of addiction.