The ventral CA2 region of the hippocampus and its differential contributions to social memory and social aggression.

The dorsal and ventral regions of the CA1 field of the hippocampus play distinct roles in the encoding of cognitive vs. emotional behaviors, respectively. Whether this distinction applies to other hippocampal fields and other behaviors is unclear. Here, we focus on the hippocampal CA2 field and compare the properties and behavioral roles of its dorsal (dCA2) and ventral (vCA2) regions. Although dCA2 is known to be required for social memory and to promote social aggression, the role of vCA2 is unknown. We report that a defined CA2 region extends to the extreme ventral pole of the hippocampus, with certain distinctions to dCA2. Unlike dCA2, chemogenetic silencing of vCA2 pyramidal neurons did not impair social memory. Similar to dCA2, vCA2 was required to promote social aggression. Thus, consistent with the CA1 region, CA2 may be differentially tuned to support cognitive compared with emotional processes along its dorsal to ventral axis.