To determine the effects of early undernutrition on learning and long-term memory, Swiss mice were cross-fostered randomly at birth to produce litter sizes of 6 and 16, thereby providing “normally nourished” and “undernourished” conditions. At 28 days of age, the pups were housed in groups of 3 and 4, with ad-lib access to food and water until testing began at 60 days of age. Each mouse received 50 active-avoidance training trials daily for 14 consecutive days. Retention testing began 14 days (...) after the end of original training and consisted of 50 trials daily for 5 days. Overall, mice reared in large litters suffered deficits in learning but not in long-term memory. (shrink)