Revenge during intergroup conflict is a human universal, but its neurobiological underpinnings remain unclear. We address this by integrating functional MRI and measurements of endogenous oxytocin in participants who view an ingroup and an outgroup member's suffering that is caused mutually (Revenge group) or by a computer (Control group). We show that intergroup conflict encountered by the Revenge group is associated with an increased level of oxytocin in saliva compared to that in the Control group. Furthermore, the medial prefrontal activity in response to ingroup pain in the Revenge group but not in the Control group mediates the association between endogenous oxytocin and the propensity to give painful electric shocks to outgroup members, regardless of whether they were directly involved in the conflict. Our findings highlight an important neurobiological correlate of revenge propensity, which may be implicated in conflict contagion across individuals in the context of intergroup conflict.

The debate regarding whether women are more empathetic than men has broad scientific, social, and clinical implications. However, previous independent questionnaires and brain imaging studies that tested different samples reported inconsistent results regarding sex/gender differences in empathic ability. We conducted three studies to investigate sex/gender differences in empathic ability using large-sample questionnaire and electroencephalography (EEG) measures. We showed that estimation of empathic ability using the interpersonal reactivity index questionnaire showed higher rating scores in women than men in all studies. However, our EEG measures of empathy, indexed by both phase-locked and non-phased locked neural responses to others' painful (vs. neutral) facial expressions, support a null hypothesis of the sex/gender difference in empathic ability. In addition, we showed evidence that priming social expectations of women and men's ability to share and care about others' feelings eliminated the sex/gender difference in questionnaire measures of empathic ability. Our large-sample EEG results challenge the notion of women's superiority in empathy that is built based on subjective questionnaire measures which are sensitive to social desirability. Our findings indicate that whether the notion of women’s superiority in empathic ability reflects a biological/social difference between women and men or a gender-role stereotype remains an open question.

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