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Sex differences in social synchronization of conditioned fear

Coordinated behaviors are prevalent in the animal kingdom as they promote the survival of social specie. Meanwhile, the distinct social roles of males and females predict sex differences in behavioral coordination. Because of its complexity, behavioral coordination and the underlying circuits have not been studied extensively in laboratory animals. Recently, we established a mouse model of social synchronization of conditioned fear, which revealed a sex difference and identified the ventral hippocampus to the amygdala pathway as the integrator of the affective and social information. Here, we investigated the sex differences further by manipulating the social cues or emotional state. Familiarity with social cues increased fear synchrony in male but not female dyads. The emotional distress from brief immobilization disrupted fear synchrony in males but enhanced it in females. Finally, inactivation of the ventral hippocampus abolished fear synchrony in both sexes but elicited negative synchrony in females only. These findings reveal that conspecific identity and emotional state are sex-specific modulators of social synchrony, suggesting sex-specific functions within the socio-emotional integrator, which includes the ventral hippocampus and yet unknown circuits.