Acquisition and retention of a passive-avoidance task as a function of age in mice

In Experiment I groups of mice between 16 to 100 days of age were tested for retention of a passive-avoidance response between 1 min and 96 hr following a single training trial at 2 shock intensities. In general, although almost all age groups displayed reliable retention at all retest intervals, some retention losses were found among the youngest age groups at the longer retention intervals. Higher shock intensity resulted in longer retest latencies, primarily among the youngest mice. In Experiment II mice 16, 25, and 100 days of age were trained to criterion on the passive-avoidance task and retested on a single trial following retention intervals of 24, 96, 192, and 384 hr. Young mice exhibited severe retention losses relative to 100-day-old mice at the longer intervals, even though they did not show deficiencies in acquisition. Neurological maturity at the time of original training appears to account for the age-related memory differences.