Age and interstimulus interval in forward and backward long-trace taste-aversion conditioning.

Rats, 70-79 days old and 477-557 days old, experienced either a forward or backward taste-aversion conditioning trial with a 15-min. or 45-min. interstimulus interval. Forward conditioning was evident in both age groups at both interstimulus intervals. Backward conditioning was evident in both age groups only at the 15-min. interstimulus interval. The failure to obtain backward conditioning at the 45-min. interval was attributed to the effect of stress, produced by injection of the US, on long-trace conditioning. As reported with forward conditioning, stress may alter metabolic rate such that the intervals at which associations can be formed are shortened.