Individual differences in the attribution of incentive salience to a reward-related cue: influence on cocaine sensitization.

When a discrete cue (a "sign") is presented repeatedly in anticipation of a food reward the cue can become imbued with incentive salience, leading some animals to approach and engage it, a phenomenon known as "sign-tracking" (the animals are sign-trackers; STs). In contrast, other animals do not approach the cue, but upon cue presentation go to the location where food will be delivered (the goal). These animals are known as goal-trackers (GTs). It has been hypothesized that individuals who attribute excessive incentive salience to reward-related cues may be especially vulnerable to develop compulsive behavioral disorders, including addiction. We were interested, therefore, in whether individual differences in the propensity to sign-track are associated with differences in responsivity to cocaine. Using an autoshaping procedure in which lever (conditioned stimulus) presentation was immediately followed by the response-independent delivery of a food pellet (unconditioned stimulus), rats were first characterized as STs or GTs and subsequently studied for the acute psychomotor response to cocaine and the propensity for cocaine-induced psychomotor sensitization. We found that GTs were more sensitive than STs to the acute locomotor activating effects of cocaine, but STs showed a greater propensity for psychomotor sensitization upon repeated treatment. These data suggest that individual differences in the tendency to attribute incentive salience to a discrete reward-related cue, and to approach and engage it, are associated with susceptibility to a form of cocaine-induced plasticity that may contribute to the development of addiction.