Norway rat pups, 15 days of age and older, huddle preferentially with members of their own species. This normal filial response can be reassigned, however, by altering the olfactory characteristics of the mother. The present series of experiments was designed to isolate those aspects of maternal stimulation that establish the filial huddling preferences of rat pups. Results of two-choice huddling tests indicated that daily, 4-hr exposures to a perfumed foster dam induced filial preferences for odors associated with maternal care. Similar effects were also achieved with equal amounts of "mere exposure" (familiarization) to odors. Different kinds of odor-experience pairings were evaluated with a within-subject regime of alternating, daily exposures. It was found that preferences induced by maternal contact are stronger than those resulting from familiarization. We rejected the hypothesis that the nursing relationship is a necessary or contributory factor in the establishment of the rat's filial attraction; preferences for odors associated with a nonlactating foster mother were as strong as those derived from maternal contact that included nutritive nursing. Contact interactions with an inanimate, warm, scented tube induced preferences as strong as those induced by maternal care. It was concluded that thermotactile stimulation during mother-young interactions induces olfactory preferences in the weanling rat.

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