Emotional contagion and helping behavior: Learning to be good recruits cell subpopulation in the dorsal hippocampus in mice

Emotional contagion, the capacity to internally simulate another's emotional state, plays a crucial role in modulating prosocial behavior. This includes rescue behaviors, wherein individuals in a safe context intervene to release a trapped conspecific from an aversive context. However, little is known about how the perceived emotional arousal of the distressed individual influences the helper's behavior and the underlying neuronal mechanisms driving prosociability. This study explores the involvement of the dorsal hippocampus (dHPC), associated with contextual learning, in emotionally charged helping in mice. Male and female mice were trained to rescue a distressed familiar conspecific of the same sex by opening a door under two conditions: the trapped mouse in a dry or flooded chamber. Cold water in the flooded chamber induced higher emotional arousal in the victim, resulting in reduced latency for rescuing by the helper. Silencing the dHPC prior to sessions significantly impaired rescue behavior, increasing latency and reducing the total number of helpers. C-fos expression after dHPC silencing suggested that emotional processing related areas were less engaged during the task. A decoder model, trained with 1-p calcium imaging and manually annotated behavioral data, revealed that ~10% of dHPC cells exhibited correlated activity with helping behavior, showing increased activity after the release of the victim. The number of task-related cells decreased over days, with higher engagement on the first day. These findings suggest that the dHPC is engaged during learning of rescue behavior, hinting at a contextual or episode-like memory component in the acquisition of this behavior.