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Incentive sensitisation theory (IST) claims that the mechanism of reward is comprised of separate neurobiological systems of wanting and liking, that dependent drug use occurs as a result of sensitisation of the system controlling wanting, and that the two systems can be dissociated. To test the IST prediction that wanting and liking for alcohol can be dissociated in humans. Measures of wanting and liking for alcohol were obtained in three experiments. Experiment 1 examined whether liking for alcohol was associated with levels of wanting, as indexed by self-reported weekly alcohol intake. Experiments 2 and 3 also assessed the association between liking and wanting but in these experiments wanting was also indexed by alcohol consumption in the laboratory. Experiment 2 increased wanting for alcohol using an alcohol priming dose to determine whether liking would be similarly affected. Experiment 3 reduced liking for alcohol by adulterating drinks with Tween to see whether wanting would also be reduced. Little evidence for an association between liking and wanting for alcohol was found in Experiments 1–3 but, collapsing across all experiments, a weak positive correlation between liking and wanting was found. However, in Experiment 2, wanting was increased by the alcohol priming dose whereas liking was not and in Experiment 3 liking was reduced without a concurrent reduction in wanting. Although correlations between wanting and liking can be observed these results support the contention of the IST that wanting and liking for alcohol can be dissociated in human participants.

Recent experiments with human subjects have shown that drug cues (e.g. sight of beer or needle and syringe) elicit different responses than do neutral stimuli. However, because conditioning has not been carried out in the majority of cases, it is not clear why drug cues have different response eliciting capacities; associative and non-associative mechanisms may both play a part. In this experiment a counterbalanced differential conditioning procedure was used to isolate the role of associative processes in the development of physiological, behavioural, and subjective conditioned responses to cues for alcohol over the course of repeated conditioning sessions. Twelve healthy volunteers took part in the experiment which involved each subject attending for ten sessions. On physiological measures evidence was found for conditioning of skin conductance and cardiac inter-beat interval responses to cues for alcohol delivery. Over the course of conditioning on behavioural measures of drink consumption there were changes in the rate of consumption and number of sips taken as a function of whether or not the drinks contained alcohol. Finally, on subjective measures, there was a differential change in subjective state in response to alcohol and soft drink expectancy as conditioning progressed.

Different kinds of physiological response to stimuli which have been associated with alcohol ingestion have been observed in human subjects. A literature review shows that when subjects are exposed to alcohol associated stimuli without consuming the drinks then increases in arousal, as indexed by skin conductance and heart rate increases, tend to occur. If subjects consume drinks which have been associated with alcohol ingestion, then decreases in arousal tend to occur. Forty non-dependent drinkers were asked to either consume or hold drinks which either had a history of alcohol association or did not. Interactions were observed between the activities subjects engaged in with the drinks and the degree of alcohol association of the drinks. Presentation of alcohol associated drinks produced smaller increases in arousal than non-alcohol associated drinks if the drinks were consumed but vice versa if the drinks were just held. The results support the conclusions drawn from the literature review and have implications for current theories of conditioned responses to drug cues and the related theories of the motivational processes involved in the regulation of drug intake.

Animal studies have demonstrated decreased reward responsivity during nicotine withdrawal (e.g., Epping-Jordan et al., Nature 393:76-79, 1998) and the Card Arranging Reward Responsivity Objective Test (CARROT) has recently been used to study the effect of nicotine withdrawal on reward responsivity in humans (e.g., Al-Adawi and Powell, Addiction 92:1773-1782, 1997; Powell et al., Biol Psychiatry 51:151-163, 2002). We investigated a suggestion that nicotine withdrawal may have additional reward-related effects apart from the reward responsivity effects already observed.The objective of this study was to determine whether or not nicotine withdrawal results in slower improvements in performance on a card-sorting task over a series of trials.We carried out two experiments using a modified version of the CARROT, the mCARROT, to compare the performance of human participants in nicotine withdrawal with those who were satiated.Although withdrawal produced no direct effect on the mCARROT measure of reward responsivity, the overall sorting rate was lower, and the increase in sorting rate across successive trials was slower during nicotine withdrawal than during satiation.These data indicate that nicotine withdrawal impacted on task performance independently of the introduction of a performance contingent reward, suggesting a novel reward-related effect of nicotine withdrawal.