Developmental change in reversal learning of an olfactory discrimination

Abstract

We examined developmental changes in the reversal of a learned discrimination in an olfactory conditioning paradigm in three experiments. Preweanling rats were exposed to an odor (CS+) paired with footshock and a different odor (CS−) that was explicitly unpaired with footshock. The rats were then immediately tested for their preference between the CS+ and CS− odors. In Experiment 1, animals trained at 12 or 18 days of age showed equivalent conditioned aversions to the CS+. When the significance of the cues was reversed, the younger animals showed rapid reversal learning; that is, their aversion to the original CS-I- was displaced by an aversion to the original CS−. However, the 18-day-old animals were slower to acquire discrimination reversal. In Experiment 2, a similar pattern of results emerged when animals were given separate preference tests involving the CS+ versus a novel odor, or the CS− versus a novel odor. In Experiment 3, intact 18-day-old rats and 18-day-olds with damage to the septum and fornix showed equivalent conditioned aversions to the CS+. In contrast to the intact animals, however, the lesioned rats showed rapid reversal of the discrimination, which resembled that of intact 12-day-olds. Thus, there appears to be a dramatic change in reversal learning of conditioned odor aversions in rats after the second week of postnatal life. These data are discussed with reference to the role of septo-hippocampal maturation in the ontogeny of olfactory learning.