Individual Variation in the Extent to Which Drug Cues Acquire Control Over Motivated Behavior.

Abstract

Cues associated with natural or drug rewards can acquire such powerful control over behavior that individuals sometimes have difficulty resisting them. Indeed, the ability of reward-related cues to motivate excessive behavior has been implicated in drug addiction, obesity, and binge eating. There is, however, considerable individual variation in the influence of reward-associated cues on behavior. We have argued that this is due, in part, to individual variation in the degree to which reward-related cues acquire incentive motivational properties (are attributed with incentive salience), and thus acquire the ability to act as incentive stimuli. For example, if a localizable stimulus (the conditional stimulus, [CS]) is repeatedly paired with delivery of a food reward (the unconditional stimulus, [US]) the food cue itself becomes attractive, eliciting approach and engagement with it in some rats (sign-trackers, STs). However, in other rats the food cue itself is not attractive, but instead upon CS presentation these animals approach the location where food will be delivered (goal-trackers, GTs). Yet other rats vacillate between the cue and the goal. A localizable food cue is also a more effective conditional reinforcer, and is more effective in reinstating food-seeking behavior, in STs than in GTs. Thus, only in some animals does a predictive cue also acquire the properties of an incentive stimulus. Recent studies suggest that the propensity of animals to attribute incentive salience to a food cue predicts the extent to which a drug cue acquires incentive properties. While there is now considerable evidence for individual variation in the extent to which a classically conditioned food cue is attributed with incentive salience, there is much less information concerning individual variation in the extent to which classically conditioned drug cues acquire incentive motivational properties. This dissertation will address the following questions: 1) Does individual variation in the tendency to attribute incentive value to a food cue predict the tendency to attribute incentive value to a classically conditioned drug cue? and 2) Are there differences in the ability of food and drug cues that are predictive vs. ones that also acquire incentive motivational properties to engage brain reward systems?