Central amygdala mediates social modulation of on-going behavior
Human empathy emerges over phylogeny from various behavioral precursors. One of the simplest is emotional contagion, i.e. sharing emotional states between individuals. Tuning one’s emotional state to that of another increases the probability of similar behavior, which thereby allows for a rapid adaptation to environmental challenges. Emotional contagion, commonly observed in animals, is well described at the behavioral level, but the neural circuits necessary for sharing emotions are not well understood. To study neural circuits underlying emotional contagion we have developed behavioral rat models of adult, same-sex social interactions that induce positive emotions, active fear and passive fear. The neural circuits in the central nucleus of the amygdala (CeA) are crucial for both appetitively and aversively motivated non-social behaviors. In the latter case the CeA mediates both active and passive defensive responses. To test the hypothesis that the neural circuits of the CeA are necessary for socially transferred emotions of different valence we used c-fos-driven targeting of channelrhodopsin and halorhodopsin to activate or inhibit neurons involved in social interactions. We show that activation of the CeA neurons involved in social interactions of different emotional valence in a novel environment resulted in distinct behavioral patterns. Activation of the CeA “positive” neurons increased exploration of the environment, activation of the “passive fear” neurons motivated rats to hide and activation of the “active fear” neurons enhanced risk assessment behavior. Inhibiting the CeA neurons led to opposite effects. Taken together, our results show that the neural circuits within the CeA control socially transmitted emotions and their impact on on-going behavior. Social emotions of different valence involve subpopulations of CeA neurons that are, at least partially, distinct. FINANCIAL SUPPORT: the National Science Centre grant 2013/11/B/NZ3/01560, European Research Council Starting Grant.