Empathy with another’s pain is an important social glue for maintaining interpersonal relationships. In most previous studies investigating the sharing of pain, a signal conveying a painful experience is presented by a target (“sender”) as a stimulus to a participant (“receiver”), and the emotional/physiological responses of the participant are measured. However, this unilateral “sender-receiver” paradigm does not adequately address the possible bidirectional experience of shared pain accruing from interaction. Our aim was therefore to investigate the bidirectional effects of sharing pain in social settings. Thirty-six unfamiliar pairs were simultaneously and repeatedly exposed to the same pain-provoking (thermal) stimuli, either in a face-to-face or a “shielded” condition where a partition prevented the partner’s responses from being fully observed. We recorded the blood volume pulse of each participant to measure the acute sympathetic response while a pair of participants experienced the stimuli simultaneously. The results revealed that participants with weaker reactions elevated their physiological reactivity to the stimulus in accordance with their partner’s reactions in the face-to-face condition. The pair-level physiological similarity was also higher compared to the shielded condition. Such a low-to-high physiological convergence may underlie the collective elevation of pain expressions, which is often observed in interactive settings.
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