Motivation for alcohol assessed by multiple variable interval schedule behaviour: effects of reward size and alcohol cues

Altered motivation for drugs of abuse is a central feature of most definiti ons of drug dependence and the impact of drug-related cues on motivation is of current interest. However, since most studies of cue-reactivity have no t used behavioural measures of motivation, their results are often difficul t to interpret in motivational terms. In the current paper we describe two experiments in which a behavioural technique, based on multiple variable in terval (VI) schedules of reinforcement, was used to study motivation for al cohol in human subjects. In both experiments, subjects attended for several sessions and, during each session, were exposed to a 6-ply VI schedule (va lues ranged from 1 to 720 s), during which they earned points that were lat er exchanged for a preferred beer or lager, In Experiment 1 the procedure w as validated by showing that changes in the magnitude of reinforcement alte red behaviour appropriately. In Experiment 2 we found evidence that the pre sence of an alcohol-related cue increased the value of alcohol rewards. The results are discussed with reference to a model for the behavioural effect s of drug-related cues in triggering relapse and a number of problems we fo und in using the multiple variable interval schedule procedure. (C) 2001 Li ppincott Williams & Wilkins.