The Effects of Early Life Stress on Context Fear Generalization in Adult Rats

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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.

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