Neuronal Responses to Conspecifics in the Ventral CA1

Conspecific recognition and discrimination is a vital aspect of social interactions. Genetic manipulations have implicated the CA2 sub-field and ventral hippocampus in rodent social memory. However, little is known about the nature of hippocampal responses to social signals. We characterized ventral CA1 responses in rats while interacting with conspecifics across a gap. Many cells showed unusual "social presence responses," i.e., large elevations of firing rates, which were contingent on the presence of a conspecific. Sharp-wave ripple activity was also increased by conspecific presence. The cells were modulated by facial touch and ultrasonic vocalizations. In male rats, female conspecifics evoked stronger responses than males. In addition, responses to females differed more strongly between individual females than between males. Cells showed little response to object presence. Ventral CA1 responses were also markedly different from those of dorsal CA1, where most cells were weakly inhibited by conspecific presence.