Multiple context discrimination in adult rats: sex variability and dynamics of time-dependent generalization of an aversive memory

Memory generalization can be defined as the transference of conditioned fear responses to novel contexts. It happens in systems consolidation, a time-dependent reduction of discrimination precision due to the rearrangement of brain regions supporting memory retrieval. To better understand the fine temporal structure of this process in different sexes, young adult female and male rats were trained in a contextual fear conditioning task and tested in the conditioning or in three novel contexts either 2, 28 or 45 days later. A set of neutral contexts was selected and graded levels of fear expression compared to the training context was obtained, albeit observed only in males, not females, in a recent memory test - the first of a number of sexual dimorphisms detected. This asymmetry, however, disappeared over time due to partial generalization, with fear converging to similar, higher values, grouped in two levels, in both sexes. In all experiments, females were better discriminators and displayed lower fear responses than males, apparently valuing different sensory modalities. This is the first study to compare fear responses between adult female and male rats retrieving recent or remote memories in multiple neutral contexts, allowing several dimorphic findings.