Using the context preexposure facilitation effect to study long-term context memory in preweanling, juvenile, adolescent, and adult rats

• Context memory persists in the context preexposure facilitation effect (CPFE).
• Context memory persists for 22 days in adult but for only 15 days in juvenile rats.
• The CPFE may be useful for studying the neural basis of infantile amnesia.

The present study used the context preexposure facilitation effect (CPFE) to examine long-term retention of incidental context learning in periweanling, adolescent and adult rats. The CPFE is a variant of contextual fear conditioning in which encoding the context representation, associating this representation with shock, and expressing the context–shock association each occur on separate occasions. Experiment 1 manipulated the retention interval—1 d, 8 d, 15 d, or 22 d—between context preexposure and training with immediate shock to determine how long the encoded context could be remembered (testing always occurred 24 h following training). The other factors were age—postnatal day (PND) 24 vs 31—and training group—Preexposed to the training context (Pre) vs. an alternate context (Alt-Pre). At both ages, significantly more freezing was evident in the Pre vs. Alt Pre Groups at the 24 h, 8 d and 15 d retention intervals but not at the 22 d interval, indicating that juvenile–adolescent rats remember the context for up to 15 d. In contrast, context memory persists for 22 days in adult rats (Experiment 2); and is not evident after 24 h, 8 d, or 15 d retention intervals in PND 17 rats (Experiment 3). The present study illustrates the value of the CPFE paradigm for investigations of long-term context memory in developing rats. Implications for the neurobiology of infantile amnesia are discussed.