Environmental enrichment reduces attribution of incentive salience to a food-associated stimulus

Animals reared in an enriched environment are less vulnerable to abuse-like behavior and exhibit less persistent drug seeking, perhaps due to a decrease in the incentive value of stimuli associated with reward. The present study investigated the effects of environmental enrichment on Pavlovian conditioned approach (PCA) performance, a measure of incentive salience attribution. Rats were first reared from postnatal day 21 to postnatal day 51 in either an enriched environment with large cages, social cohorts and novel objects, or in an isolated environment with small, hanging cages, no social cohorts and no novel objects. Rats were then trained on a PCA task for 5 consecutive days, where a retractable lever was predictive of a food reward. Isolated rats predominantly exhibited sign-tracking responses directed toward the reward-predicted lever (indicative of incentive salience attribution), while enriched rats predominantly exhibited goal-tracking responses directed toward the location of food delivery. Both groups learned their respective response type at equal rates. The results indicate that environmental enrichment reduces the readiness to attribute incentive value to reward-associated cues, which may explain the enrichment-induced protection against addiction-like behaviors. (C) 2011 Elsevier B.V. All rights reserved.