Familiar contextual odors promote discrimination learning in preweanling but not in older rats

For rats 16- or 28-days-old postnatal, we tested the source of the facilitation in instrumental learning provided by odors from home nest materials. Three experiments confirmed that acquisition of a spatial discrimination (to escape footshock) was facilitated not only by the presence of typical nest odors in the training context, but also by the presence of a non-rat odor (banana) to which the animals had been familiarized for 4 hr/day for 7 days. There was a borderline tendency for a similar facilitation after familiarization to the latter odor for only 10 min. These effects occurred for rats 16 days postnatal but not for those 28 days old. The experiments also confirmed that the prior exposure to non-rat odors did not in itself, in the absence of that odor during learning, affect discriminated escape learning, and that enhanced affinity for a contextual odor is not a sufficient condition for enhancement of learning in its presence. There was some indication that the 16-day-old rat was more likely to select a discriminative odor to guide their choice of spatial locations if a familiar contextual odor was present.