Drug Effects on Preference and Reward

Study Summary

Classical conditioning is widely used to study motivational properties of addictive drugs in animals, but has rarely been used in humans. Here, we are establishing a procedure suitable for studying the neurobiology and individual determinants of classical conditioning in humans. Healthy volunteers are randomly assigned to four groups that received methamphetamine or placebo in the presence of distinctive environmental cues under paired or unpaired conditions. During each session, subjects perform tasks known to activate the ventral striatum in fMRI studies. The tasks are performed in the presence of a distinctive context, consisting of a screen background image of a beach or of mountains, accompanied by corresponding sounds. Separate groups of subjects carry out the tasks under high or low reward conditions. Within each of the two reward conditions, one group (paired), receives methamphetamine (20 mg, oral) or placebo consistently associated with one of the contexts, while the other (unpaired) receives drug or placebo unrelated to context. A fifth group (paired) perform the tasks with contextual cues but in the absence of monetary incentives. Before and after conditioning, participants carry out a series of forced choice tasks, and change of preference over time was analyzed.

Primary Outcome

Subjects rate their preference for several pairs of stimuli before and after conditioning pairings. The stimuli are presented on a computer screen in the pre and post preference tests, and the change in preference after the conditioning trials is the primary outcome measure.

Interventions

• BEHAVIORAL Pairing condition