Conditioned effects of environmental stimuli paired with smoked cocaine in humans

Rationale: Clinical data suggest that stimuli paired with cocaine use acquire emergent stimulus effects, such as the ability to elicit cocaine craving. Objectives: The purpose of this study was to determine the conditioned effects of neutral stimuli paired with cocaine smoking. Methods: Eight experienced adult cocaine smokers participated in 22 experimental sessions while residing on a Clinical Research Center. One set of cues (CS–) was paired with placebo smoked cocaine and one set of cues (CS+) was paired with 25 mg smoked cocaine. Results: After 18 training trials, the effects of cocaine on heart rate and ratings of ”anxious” were greater, and skin temperature and ratings of ”tired” were smaller when compared to the effects of cocaine after the first training trial. When instructed to select a cue to experience after training, seven of eight participants selected the CS+, while only three of the participants selected the CS+ prior to training, i.e., the CS+ functioned as a conditioned reinforcer. Presentation of the CS+ alone without cocaine during extinction trials increased HR, SP, and ratings of ”anxious””tired”, and ”I want cocaine” and decreased skin temperature. These changes elicited by presentation of the CS+ decreased over the course of the extinction sessions. Conclusions: The present results indicate that classical conditioning is one mechanism by which stimuli paired with cocaine acquire emergent stimulus effects. Received: 21 April 1999 / Final version: 4 November 1999