The ventral CA2 region of the hippocampus and its differential contributions to social memory and social aggression
Although it is well-known that the hippocampus mediates declarative memory (the repository of information of people, places, things and events) and influences behavior, the differential contributions of the dorsal and ventral hippocampus to specific forms of memory and behavior remain largely unknown. Studies to date show that the dorsal hippocampal CA1 region is important for cognitive and spatial tasks whereas the ventral CA1 region is associated with affective or emotional processing. Whether other regions and forms of hippocampal-dependent memory and behavior show a similar distinction remains unclear. Here we examine how social memory and related social behaviors are encoded across the dorso-ventral axis of the hippocampus. Although recent studies show that the dorsal hippocampal CA2 region is required for social memory and acts to promote social aggression, the behavioral role of ventral CA2 remains unknown. Indeed, whether a defined CA2 region extends throughout ventral hippocampus is controversial. Here, we report that a molecularly, anatomically and electrophysiologically defined CA2 region extends to the extreme ventral pole of hippocampus, with both similarities and important differences in its projection patterns and synaptic impact compared to dorsal CA2. Of particular importance, we find that ventral CA2 is not required for social memory but is critical for promoting social aggression. These results support the view that the ventral region of hippocampus is more generally tuned for emotionally-related behaviors compared to the cognitively-tuned dorsal hippocampus.