Acquisition and retention of separate elements of a conditioned olfactory discrimination in preweanling rats

Acquisition and retention of separate elements of an olfactory discrimination were tested in 15- and 20-day-old preweanling rats. Four or 8 conditioning trials were given in Experiment 1. Each rat was presented one odor always followed by footshock (CS+) and another never paired with footshock (CS-). Conditioning to both stimuli was assessed through 3 types of olfactory preference tests involving comparison between CS+ and a novel odor, CS- and a novel odor, or CS+ and CS-. The results indicated that for 15- and 20-day-olds, both stimuli become excitatory early in training; further conditioning trials diminished the excitation previously accrued to the CS-, and the olfactory discrimination became apparent. When levels of conditioning were equated, retention was tested after intervals of 4 min, 3 days, or 8 days (Exp. 2). Rate of forgetting was more rapid for the 15-day-olds, but both ages of subjects showed similar patterns of forgetting, which included a progressive decrease in the aversion to the CS+ but an increase in aversion to the CS-.