The effects of early life stress on context fear generalization in adult rats

Research shows that memory for a context generalizes (i.e., becomes less precise) over time. In this series of experiments, we examined the impact of early life stress on context generalization. Early life stress was modeled using a maternal separation procedure, whereby pups were separated from the dam for 3 hr a day from postnatal Day 2 to 14, or reared as normal. In adulthood, rats were trained to fear a context, and were then tested for freezing in either the training context or a generalization context. Across 5 experiments, we found that maternally separated animals showed generalization when tested 1 day after training (Experiments 1a, 2, 3a, 3b), whereas standard reared rats discriminated at this time point (Experiments 1a & 3b). When tested 1 week after training, all rats generalized (Experiment 1b). Furthermore, maternally separated animals froze more to the training context than the generalization context when tested 1 hour after training (Experiment 2), indicating that the increased generalization expressed by these animals when tested after 1 day is not due to a general inability to discriminate. Manipulations that have been found to reduce generalization in standard reared animals failed to enhance memory specificity at the 1-day retention interval in maternally separated animals (i.e., a pretest reminder, Experiment 3a, and context preexposure, Experiment 3b). Thus, early life stress results in faster generalization that is more resistant to treatments designed to enhance memory specificity. (PsycINFO Database Record (c) 2019 APA, all rights reserved).