Ontogenetic factors in the retrieval of memories.

Although rats may show extensive forgetting if a long interval is interpolated between an aversive-conditioning episode and a retention test, this forgetting can be alleviated by a variety of reactivation treatment. This paper reports several experiments analyzing the consequences of one reactivation treatment - noncontingent presentation, between conditioning and testing, of the unconditioned stimulus - when applied to rats which differ in the age at which they are given their conditioning episode. After a long retention interval, both paradigms tested using this reactivation treatment are relatively ineffective for animals conditioned when 16--17 days of age, although both paradigms markedly alleviate forgetting when such immature animals are tested after relatively short retention intervals (a similar effect seems to occur with very old rats). Implications of this finding are tested and discussed.