Ontogenetic differences in short-term retention of Pavlovian conditioning

In the present series of studies 16- and 21-day-old rats acquired an aversion to a black compartment (CS+) paired with footshock, only if given preconditioning exposure to a white chamber (CS-) not paired with footshock. The strength of conditioning was inversely related to the length of the retention interval in both age groups. However, the rate of forgetting was accelerated in the 16-day-old subjects, indicating infantile amnesia for the conditioned aversion. Strength of conditioning was also inversely related to the length of the CS-/CS+ interval in both age groups, indicating that expression of the aversion is critically dependent on an active memory of the CS- at the time of conditioning. Additionally, there was an ontogenetic decrease in the rate of forgetting of the CS-, indicating infantile amnesia for elements of the conditioning episode that did not predict occurrence of US.