When making judgments in a group, individuals often revise their initial beliefs about the best judgment to make given what others believe. Despite the ubiquity of this phenomenon, we know little about how the brain updates beliefs when integrating personal judgments (individual information) with those of others (social information). Here, we investigated the neurocomputational mechanisms of how we adapt our judgments to those made by groups of different sizes, in the context of jury decisions for a criminal. By testing different theoretical models, we showed that a social Bayesian inference model captured changes in judgments better than 2 other models. Our results showed that participants updated their beliefs by appropriately weighting individual and social sources of information according to their respective credibility. When investigating 2 fundamental computations of Bayesian inference, belief updates and credibility estimates of social information, we found that the dorsal anterior cingulate cortex (dACC) computed the level of belief updates, while the bilateral frontopolar cortex (FPC) was more engaged in individuals who assigned a greater credibility to the judgments of a larger group. Moreover, increased functional connectivity between these 2 brain regions reflected a greater influence of group size on the relative credibility of social information. These results provide a mechanistic understanding of the computational roles of the FPC-dACC network in steering judgment adaptation to a group’s opinion. Taken together, these findings provide a computational account of how the human brain integrates individual and social information for decision-making in groups.

当在一个小组中做出判断时，个人通常会修改自己对最佳判断的信念，从而根据他人的信念做出判断。尽管这种现象无处不在，但我们对将个人判断（个人信息）与他人判断（社会信息）相结合时大脑如何更新信念知之甚少。在这里，我们研究了在罪犯的陪审团决定的背景下，如何使我们的判断适应由不同规模的群体做出的判断的神经计算机制。通过测试不同的理论模型，我们证明了社会贝叶斯推理模型比其他两个模型更好地捕获了判断的变化。我们的结果表明，参与者通过根据各自的可信度适当权衡个人和社会信息来源，从而更新了他们的信念。在调查贝叶斯推断的2种基本计算，信念更新和社会信息的可信度估计时，我们发现背前扣带回皮质（dACC）计算了信念更新的水平，而双侧额叶皮质（FPC）则更多地参与了为更大的群体的判断赋予了较高的信誉。此外，这两个大脑区域之间的功能连接性增加反映了小组规模对社交信息相对可信度的更大影响。这些结果提供了对FPC-dACC网络在指导决策适应小组意见方面的计算作用的机械理解。在一起