In daily life, trust is important in interpersonal interactions. However, little is known about interpersonal brain synchronization with respect to trust; in particular, the differences between individuals with and without siblings are not clear. Therefore, this study applied functional near-infrared spectroscopy hyperscanning in a sequential reciprocal-trust task. We divided pairs of participants (strangers) into two groups according to their only-child status. The two strangers interacted with one another in an online trust game while their brain activities in the medial prefrontal cortex (mPFC) and the right temporoparietal junction (rTPJ) were measured. The behavioral results revealed that compared with the non-only-child group, the only-child group exhibited lower repayment, less reciprocation, and less cooperative decisions during the process. In addition, the brain imaging results showed that the interpersonal synchronization of the mPFC in the only-child group was significantly weaker than that in the non-only-child group. Our findings demonstrate neurobehavioral support for the only-child effect in terms of the trust by revealing that an only child shows less trust than does a non-only-child, resulting in lower inter-brain coherence.

在日常生活中，信任在人际互动中很重要。然而，关于信任的人际大脑同步知之甚少。特别是，有兄弟姐妹与没有兄弟姐妹的个体之间的区别尚不清楚。因此，本研究在顺序互惠任务中应用了功能近红外光谱超扫描。我们根据参与者的独生子女身份将参与者（陌生人）对分为两组。这两个陌生人通过在线信任游戏相互互动，同时测量了他们在前额内侧皮层（mPFC）和右侧颞顶交界处（rTPJ）的大脑活动。行为结果表明，与非独生子女组相比，独生子女组的还款额更低，往返次数更少，以及在此过程中较少的合作决策。此外，大脑成像结果显示，独生子女组中mPFC的人际同步明显弱于非独生子女组。我们的发现通过揭示独生子女比非独生子女表现出更少的信任，从而降低了人脑间的连贯性，从而证明了在信任方面对独生子女效应的神经行为支持。