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Conditioning of an odor aversion in preweanlings with isolation from home nest as the unconditioned stimulus.

Four experiments assessed the acquisition of aversions by preweanling rats to odors experienced during isolation from their home-nest environment. Conditioned aversion occurred for animals given a second novel odor paired with the home-nest environment, depending upon the duration of the odor-isolation pairing. With a brief duration of pairing (two pairings of 3 min each) novel odors became more preferred when paired with isolation or, to a lesser extent, when paired with home. With longer durations of pairing (two pairings of 4 hr each) the odor paired with isolation became absolutely aversive, although the odor paired with home did not become absolutely preferred. With intermediate durations neither aversion nor preference for the odors was substantial. Animals conditioned at ages 9, 16, or 23 days postnatal acquired aversions to odors paired with isolation, but 30-day-old rats did not.