Human cooperation behavior based on reciprocal altruism has been a hallmark of ancient and modern societies. Prior studies have indicated that inter-brain synchronization (IBS) between partners could exist during cooperation. However, how the sex composition of dyads influences the neural synchronization is still poorly understood. Here, we adopted functional near-infrared spectroscopy (fNIRS) based hyperscanning and a task of building blocks to investigate the sex composition effect on IBS in face-to-face cooperation in a natural situation, by evaluating brain-to-brain interactions of forty-five same-sex and mixed-sex dyads. Results showed significantly stronger inter-brain synchronization in Brodmann area 10 (BA10) in cooperation. In addition, variance analysis indicated that only male-male dyads showed increased inter-brain synchronization in left inferior frontal region (i.e., BA10) specific to cooperation. More importantly, the inter-brain synchronization in male-male dyads was significantly greater than that in male-female and female-female dyads. These findings provide support for the impact of sex composition on social cooperation in a naturalistic interactive setting and extend our knowledge on the neural basis of face-to-face cooperation.

基于互惠利他主义的人类合作行为一直是古代和现代社会的标志。先前的研究表明，合作伙伴之间的大脑间同步 (IBS) 可能存在于合作过程中。然而，对二元体的性别构成如何影响神经同步仍知之甚少。在这里，我们采用基于功能性近红外光谱 (fNIRS) 的超扫描和积木任务，通过评估 40 个人的脑对脑相互作用，研究在自然情况下面对面合作中性别构成对 IBS 的影响-五个同性和混性二人组。结果显示，合作时 Brodmann 10 区 (BA10) 的大脑间同步性显着增强。此外，方差分析表明，只有男性-男性二元组在左下额叶区域（即 BA10）中显示出针对合作的大脑间同步增加。更重要的是，男性-男性二元组的大脑间同步性明显高于男性-女性和女性-女性二元组。这些发现为自然互动环境中性别构成对社会合作的影响提供了支持，并扩展了我们对面对面合作的神经基础的认识。