Postrhinal cortex contributions to the expression of auditory fear conditioning.

The postrhinal cortex (POR), the rodent homologue of the primate parahippocampal cortex (PHC), has been implicated in contextual and spatial processing. For instance, prior studies have demonstrated that permanent lesions of POR impair contextual fear conditioning. In contrast, permanent lesions of POR, specifically prior to training, do not impact auditory fear conditioning. In the current experiments, we examined the role of POR in the expression of auditory fear conditioning by using chemogenetics to silence neural activity in POR at the time of retrieval testing. Considering that extinction is context-dependent, and POR contributes to contextual memory, we hypothesized that POR would be necessary for expression of auditory fear conditioning following extinction. We found that POR inactivation during retrieval impaired freezing to an auditory cue that was tested in the conditioning context (A) after it had been extinguished in a different context (B). However, the involvement of POR was not specific to extinction. POR inactivation also impaired freezing to an auditory fear cue that had not undergone extinction. Thus, while prior studies have identified a role for POR in contextual fear conditioning, the current findings extend the functional role of POR to include the expression of auditory fear conditioning.