Effects of delayed testing on passive avoidance of conditioned fear stimuli in young rats

Abstract

Deficits in passive avoidance learning in immature animals have been explained in terms of immature response-inhibition mechanisms, the role of age-specific defense responses to conditioned or unconditioned stimuli, or differential levels of fear acquisition. In Experiment 1, shock-elicited UCRs and fear strength were held constant by training all subjects at the same age. Sixteen-day-old rat pups received Pavlovian fear conditioning and were tested 1, 5, or 10 days later for passive avoidance of the conditioned stimuli. To offset retention losses, half of each group received a noncontingent footshock reactivation 24 h before testing. Passive avoidance latencies increased with delay (age) in reactivated groups. But with an active avoidance (escape from fear) measure (Experiment 2), performance was consistently poor and unrelated to age at testing. These data suggest that maturation of response-inhibition mechanisms may contribute to the ontogeny of passive avoidance performance. More generally, some implications of the distinction between learning and performance for developmental studies are considered. © 1981, The psychonomic Society, Inc.. All rights reserved.