Temporal Dynamics of Associative Contextual Fear Memories Storage in Mice

This study investigated the dynamics of long-term contextual fear memory in mice. Animals were trained to associate a novel context with footshock and tested under two paradigms. In the single-test paradigm, independent groups were tested once at different time points (1 day to 6 months post-training) to assess memory stored without prior retrieval. In the repeated-test paradigm, the same mice were tested six times over 73 days to evaluate the impact of multiple retrieval and reconsolidation episodes on memory persistence. In single testing, contextual memory peaked in behavioral expression between days 14 and 28, remained detectable for up to 3 months, and was no longer expressed by 6 months. In contrast, repeated retrieval prevented memory decay over time. However, memory expression followed a similar temporal profile, reaching a maximum between days 14 and 28. These findings suggest that the contextual memory engram continues to mature until approximately day 14 post-training, independent of retrieval. By one month, the memory transitions into a remote, stable form. Without retrieval, such memory gradually fades, while repeated expression appears to stabilize it for extended periods.