NEURAL BASIS OF SPATIAL, CONTEXTUAL, AND TEMPORAL MEMORY IN THE RETROSPLENIAL CORTEX
The Retrosplenial cortex (RSC) is a brain region which plays an important role in spatial navigation and has also been shown to be involved in episodic memory in humans. Although several studies have shown the involvement of the RSC in various cognitive functions, still a lot remains to be understood about its information coding mechanisms. In this work, I examine the RSC firing patterns underlying its functions in spatial, contextual, and temporal memory. RSC is interconnected with the Hippocampus (HPC), which is also involved in similar functions. Even though both the regions are involved in navigation-related firing, there has been little work directly comparing the information coding mechanisms of these two brain regions. To address this, I examined the similarities and differences in spatial and contextual firing patterns in the two regions and found that even when encoding the same type of navigational information, they used different coding schemes. Also, head direction was prominently encoded by the RSC but not by the HPC. The results show that the RSC and HPC make related, but somewhat different contributions to spatial cognition. RSC lesions have been shown to cause impairment in temporal memory but the neuronal firing patterns supporting it have not been studied. I addressed this by analyzing archival RSC neuronal firing data during the intertrial delay period from two behavioral tasks with different memory demands. I discovered time cells in the RSC, and they are sensitive to the memory demands of the task. This suggests that temporal coding is a prominent feature of the RSC firing patterns. Lesion studies have found that the RSC is also necessary for spatial working memory tasks but the firing patterns underlying it remain unknown. To address this, I analysed the firing activity of RSC neurons while rats held spatial information in memory over the delay period of a spatial alternation task. I found that the RSC neurons exhibited reliably different firing patterns throughout the delay periods preceding each trial type, suggesting that these firing patterns represent critical memory information underlying the role of the RSC in spatial working memory.