Role of age, post-training consolidation, and conjunctive associations in the ontogeny of the context preexposure facilitation effect.

The context preexposure facilitation effect (CPFE) is a variant of contextual fear conditioning in which context learning and context-shock associations occur on separate occasions. The CPFE with an immediate shock emerges between Postnatal Day (PND) 17 and 24 in the rat and depends on hippocampal NMDA-receptor function in PND 24 rats (Schiffino et al. [2011] Neurobiology of Learning and Memory 95(2):190-198). This study investigated this ontogenetic effect further and reports three findings: First, the CPFE is absent on PND 19 but emerges modestly in rats given exposure on PND 21. Second, the absence of the CPFE on PND 17 does not reflect inability to consolidate the context-shock association established on the training day. Lastly, the CPFE on PND 24 requires exposure to the combined features of the context. These results are the first to show that the early development of contextual fear conditioning depends on conjunctive representations and that processes underlying the CPFE begin to emerge around PND 21 in the rat.