MethadoneUsersandRiskydecisions 12

Reinforcing properties of psychoactive substances are considered to be critically involved in the development and maintenance of
substance dependence. While accumulating evidence suggests that the sensitivity to reinforcement values may generally be altered in
chronic substance users, relatively little is known about the influence reinforcing feedback exerts on ongoing decision-making in these
individuals. Decision-making was investigated using the Cambridge Risk Task, in which there is a conflict between an unlikely large reward
option and a likely small reward option. Responses on a given trial were analyzed with respect to the outcome on the previous trial,
providing a measure of the impact of prior feedback in modulating behavior. Five different groups were compared: (i) chronic
amphetamine users, (ii) chronic opiate users in methadone maintenance treatment (MMT), (iii) chronic users of illicit heroin, (iv) ex-drug
users who had been long-term amphetamine/opiate users but were abstinent from all drugs of abuse for at least 1 year and (v) matched
controls without a history of illicit substance use. Contrary to our predictions, choice preference was modified in response to feedback
only in opiate users enrolled in MMT. Following a loss, the MMT opiate group chose the likely small reward option significantly less
frequently than controls and heroin users. Our results suggest that different opiates are associated with distinctive behavioral responses
to feedback. These findings are discussed with respect to the different mechanisms of action of heroin and methadone.