Abstract
Latent inhibition (LI) refers to the reduction in conditioned responding when the conditioned stimulus (CS) is preexposed prior to CS–unconditioned stimulus pairings. Experiment 1a demonstrated that preexposure to an odor CS prior to odor–shock pairings markedly reduced conditioned freezing in 25‐day‐old rats; however, this LI effect was observed only if odor preexposure and odor–shock pairings occurred in the same context (i.e., LI was context‐specific at this age). The results of Experiment 1b showed that 18‐day‐olds also exhibited LI, but this effect was not context‐specific at this age. In Experiment 2, rats were preexposed to the odor at 18 days of age and given odor–shock pairings at 25 days of age. These rats exhibited context‐specific latent inhibition, suggesting that 18‐day‐old rats encoded the preexposure context. In Experiment 3, all parameters were identical to Experiment 2, with the exception that odor–shock pairings were given at ∼PN18 and testing occurred at ∼PN25. These rats exhibited latent inhibition at test, but this effect was not context‐specific. The results of this study suggest that (a) PN18 rats can exhibit latent inhibition, and (b) the expression of context‐specific latent inhibition depends on the age at which conditioning occurs. © 2005 Wiley Periodicals, Inc. Dev Psychobiol 47: 55–65, 2005.