Unique roles for the anterior and posterior retrosplenial cortices in encoding and retrieval of memory for context.

The rat retrosplenial cortex (RSC) makes critical contributions to learning and memory but these contributions may not be uniform along its rostro-caudal axis. Previous work suggests that event-related and context-related information are differentially encoded by anterior and posterior RSC subregions. Here, we further test this idea using a procedure in which spatial/environmental cues (context) and discrete event memories are acquired separately. All animals received a 5-min pre-exposure to the training context 24 h before contextual fear conditioning where shock was delivered immediately upon being placed in the chamber. Rats were tested for memory for the context the next day. We found that optogenetic inhibition of cells in only the posterior RSC during the pre-exposure phase, when spatial information is encoded, reduced behavioral responding during the subsequent memory test. However, similar inhibition of either the anterior or posterior RSC during shock delivery, when information about both the context and the shock become integrated, impaired memory. Finally, inhibiting cellular activity in only the posterior RSC during memory retrieval during testing reduced responding. Together, these results suggest that while activity in both subregions is needed during the period in which the event-related information becomes integrated with the context representation, the posterior RSC is important for both memory formation and retrieval or expression of memory for information about the context. These results add to a growing literature demonstrating a role for the RSC in integration of multiple aspects of memory, and provide information on how spatial representations reliant on the retrosplenial cortex interact with associative learning.