Social and spatial codes in the hippocampus

The hippocampal formation is important for encoding, consolidation and retrieval of episodic memories. While integration of spatial information into episodic memories has been studied in great detail, how social information is encoded in the brain has received less attention. Emerging evidence suggests that the hippocampus area CA2 plays an essential role for social recognition memories, and previous studies show that silencing area CA2 impairs social recognition in mice. To determine how social, spatial and object information is computed in the different areas of the hippocampus, we recorded single unit activity and local field potentials from areas CA1, CA2 and CA3 in rats performing a social recognition task followed by recordings in a similar object recognition task.Preliminary data analysis confirms that most units in hippocampal regions CA1, CA2 and CA3 exhibit stable spatial representations. However, a subset of CA2 cells show unstable spatial representation when rats are exposed to a conspecific with a shift in place fields towards the location of the conspecific. However, the proportion of recorded units with social selective firing patterns seems lower in rats compared to previous reports in mice.We currently analyze population dynamics and compare the object recognition with the social recognition in order to explore differences in social coding across the regions.