Hippocampal CA2 Region: A New Player in Social Dysfunctions

Abstract

For social species, normal social cognitive functions are essential for individuals to survive in a social group. Various neuropsychiatric disorders, including schizophrenia, autism and bipolar disorder are characterized by the impairments in social cognition. The hippocampus has been at the forefront of research in learning and memory for several decades. Hippocampal dysfunction contributes to learning and memory impairments as well as a range of social dysfunctions. However, precise contributions of different hippocampal sub-regions to differential aspects of cognitive functions remain unclear. This review first describes several key features of social abnormalities related to neuropsychiatric disorders, and then introduces the behavioral tasks used in animal models to assess each feature. Second, it gives a basic description of CA2 anatomy followed by an overview of its known functions. Third, it highlights a number of recent findings that associate the abnormalities of the hippocampal CA2 area and social dysfunctions in both animal models and human patients.

The role of the right temporo–parietal junction in social decision‐making

“…Previous studies have shown that the hippocampus is implicated in the encoding, updating, and modulation of memory representations that underlies flexible behavior (Rubin, Watson, Duff, & Cohen, ; Wimmer & Shohamy, ). Especially, the hippocampus’ CA2 subregion, has been causally linked with social memory processes in an animal model (Hitti & Siegelbaum, ), underlining its relevance in social learning (Mou, ). Given these findings we suggest that the rTPJ–hippocampus connectivity indicates that mentalizing and memory formation processes co‐occur and underlie individual social learning during the game as further analyses showed.…”

Social Memory and the Role of the Hippocampal CA2 Region

“…While the other subunits of the hippocampus have received extensive attention, the CA2 region has been largely neglected, poorly understood, and for the most part, unexplained (Chevaleyre and Siegelbaum, 2010; Caruana et al, 2012; Cui et al, 2013; Stevenson and Caldwell, 2014). Recent evidence has shed light on the obscurities of the CA2, characterizing it as a distinct subregion, with its own unique afferents and efferents, cellular composition, and contribution to hippocampal processes (Cui et al, 2013; Dudek et al, 2016; Mou, 2016).…”