Your smiles inspired my smiles: the interpersonal neural coupling of positive emotion contagion during social interactions

Emotional contagion refers a process that by which the emotions of a perceiver become more similar to those of others as a result of exposure to these emotions. The present study investigated the behavioral and interpersonal neural coupling mechanisms underlying positive emotional contagion. We recruited forty-six stranger dyads and created an emotional contagion task using the fNIRS-based hyper-scanning technique to track brain activities of interactive partners (the sender, the perceiver), examining brain regions such as the prefrontal cortex and temporo-parietal junction, which are parts of the cognitive control and mirroring brain networks. In each dyad, the senders were demanded to watch positive/neutral clips or imitate the actor's non-emotional facial actions, the perceivers were demanded to observe the senders' positive/neutral facial expressions or non-emotional facial movements passively. Results revealed that interactive partners exhibited more synchronous facial expressions, higher interpersonal brain synchronizations (IBS) associated with the mirror neuron system (IFG, SMG) and the cognitive control system (DLPFC) and reported more positive emotions in the positive condition than neural condition or facial movements condition, indicating positive emotional contagion has occurred. Furthermore, the perceiver's self-rated valence scores positively mediated the relationship between facial expression synchrony and IBS of mirror neuron system between dyads (IFG_TRI _sender - left_SMG _perceiver). Our findings revealed that automatic mimicry of other's positive emotional expressions (indicating by facial expression synchronization) might be one of the mechanisms responsible for the contagion of positive emotions among strangers. We discussed the evolutional benefits of positive emotional contagion adhering to an automatic mimicry process.