Drug expectancy is necessary for stimulus control of human attention, instrumental drug-seeking behaviour and subjective pleasure

Background: It has been suggested that drug-paired stimuli (S+) control addictive behaviour by eliciting an explicit mental representation or expectation of drug availability. Aims: The aim of the present study was to test this hypothesis by determining whether the behavioural control exerted by a tobacco-paired S+ in human smokers would depend upon the S+ eliciting an explicit expectation of tobacco. Design: In each trial, human smokers (n=16) were presented with stimuli for which attention was measured with an eyetracker. Participants then reported their cigarette reward expectancy before performing, or not, an instrumental tobacco-seeking response that was rewarded with cigarette gains if the S+ had been presented or punished with cigarette losses if the S- had been presented. Following training, participants rated the pleasantness of stimuli. Results: The S+ only brought about conditioned behaviour in an aware group (those who expected the cigarette reward outcome when presented with the S+). This aware group allocated attention to the S+, performed the instrumental tobacco-seeking response selectively in the presence of the S+ and rated the S+ as pleasant. No conditioned behaviour was seen in the unaware group (those who did not expect the cigarette reward outcome in the presence of the S+). Conclusions: Drug-paired stimuli control selective attention, instrumental drug-seeking behaviour and positive emotional state by eliciting an explicit expectation of drug availability.