Optogenetic inhibition of either the anterior or posterior retrosplenial cortex disrupts retrieval of a trace, but not delay, fear memory

Previous work investigating the role of the retrosplenial cortex (RSC) in memory formation has demonstrated that its contributions are not uniform throughout the rostro-caudal axis. While the anterior region was necessary for encoding CS information in a trace conditioning procedure, the posterior retrosplenial cortex was needed to encode contextual information. Using the same behavioral procedure, we tested if there was a similar dissociation during memory retrieval. First, we found that memory retrieval following trace conditioning results in increased neural activity in both the anterior and posterior retrosplenial cortex, measured using the immediate early gene zif268. Similar increases were not found in either RSC subregion using a delay conditioning task. We then found that optogenetic inhibition of neural activity in either subregion impairs retrieval of a trace, but not delay, memory. Together these results add to a growing literature showing a role for the retrosplenial cortex in memory formation and retention. Further, they suggest that following formation, memory storage becomes distributed to a wider network than is needed for its initial consolidation.