Enhancement of conditioning by a nongustatory CS: Ontogenetic differences in the mechanisms underlying potentiation

Abstract

Three experiments examined stimulus selection in rats at various points during development. In the first experiment, preweanling, periadolescent, and adult rats were conditioned either with a black chamber alone or with an odorant present in the black chamber during conditioning. The expression of overshadowing or potentiation depended on the age of the animal and on the measure used to assess conditioning to the target CS (black chamber). Experiment 2 examined whether the rate of extinction of the odor aversion in animals conditioned with the compound (odor-black chamber) CS was age-dependent. The third experiment examined the mechanisms underlying the potentiation of contextual conditioning by examining the effect of pretest extinction of the odor aversion. The results indicated that effect of the extinction treatment was age-dependent. Extinction attenuated the aversion expressed to the black chamber in the preweanling animals, but enhanced conditioned responding to the target CS in adults. Implications of these data for two major views of potentiation are considered.