Prefrontal ensembles represent freezing of conspecifics

Social buffering is a process in which the presence of other members of the same species (conspecifics) decreases stress reactions during threat exposure. In parallel, prior reports showed that groups of individuals display synchronous actions in non-threatening situations. However, it is unknown if individuals also synchronize actions when facing threats. Prior studies showed social buffering of freezing in pairs of subjects. We now expand these findings and show social buffering of freezing during exposure to a predator and a shock grid in mice of both sexes in a larger group of four conspecifics. Furthermore, mice also displayed synchronized freezing. The presence of freezing synchrony suggests the existence of a neural representation of conspecific freezing. We reasoned that this encoding might be in the medial prefrontal cortex (mPFC), as this region has been implicated in social behaviors and freezing. Strikingly, mPFC neural activity represented the average level of freezing across conspecifics. MPFC ensembles displayed differential encoding of self and conspecific freezing, and during predator exposure the mPFC encoded the number of conspecifics freezing and conspecific freezing bout duration. These data show, for the first time, neural representation of conspecific freezing, and suggest that the mPFC may coordinate behavioral responses to threat across conspecifics.Significance Statement Social animals display attenuated threat-elicited responses when encountering threats as a group. However, it is unknown how freezing signals from conspecifics are encoded by the brain when facing threats, as prior work has been limited to studies of pairs, or assays without social interactions. We identify a neural population in the medial prefrontal cortex (mPFC) that represents conspecific freezing during grouped threat exposure, and these cells dynamically represent the duration of other animals' freezing bouts. Strikingly, the activity of these ensembles also represents the number of conspecifics freezing. These findings uncover a previously unknown function of the mPFC to encode conspecific freezing.