RESUMO
Although environmental enrichment is presumed to enhance learning, appetitive behavior may also be altered by this experience: anticipatory responding for sucrose is reduced in environmentally enriched (EE) rats [van der Harst, J.E., Baars, A.M. and Spruijt, B.M. Standard housed rats are more sensitive to rewards than enriched housed rats as reflected by their anticipatory behaviour. Behav Brain Res 2003;142:151-156]. To assess the impact of differential environmental experience on learning and appetitive behavior, we trained 17 EE and socially isolated (SI) rats in a three-phase, operant-shaping procedure for sucrose reinforcement. In phase one, a feeder cue was paired with sucrose availability. In phase two, a nose poke to either one of two lit holes on the opposing wall activated the feeder cue. In phase three, the feeder cue was elicited by a poke to a single lit hole. While acquisition rates in phase one and phase two were similar, EE animals reached phase-three criteria [completion of 100 trials in 45 min and 15 or fewer bad pokes] faster than SI animals. These two groups showed similar session completion rates, reinforced and non-reinforced licking responses, and overall behavioral activity during phase three acquisition; however, SI rats performed more bad pokes (responses to the non-lit hole after nose-poke cue onset) and intertrial interval (ITI) pokes during this training period. Because all ITI (and presumably many bad) pokes were initiated before onset of nose-poke cue, this difference indicates greater anticipatory responding in SI animals. This experience-dependent alteration in appetitive behavior may explain, in part, the tendency of SI rats to show attenuated learning rates in appetitive contexts in which complex contingencies exist.