<p>Neural activity correlated with SR.</p>

Bargaining is a fundamental social behavior in which individuals often accept unfair offers. Traditional behavioral models, based solely on choice data, typically interpret such acceptance as simple reward-maximization. However, regulating inequity aversion may also play a critical role in these decisions. Incorporating response time alongside choice data allows us to quantify participants’ internal mental effort when deciding to accept unfair offers. We conducted functional magnetic resonance imaging (fMRI) while participants played the ultimatum game, deciding within 10 s whether to accept or reject monetary offers from a proposer. Using the drift diffusion model (DDM), we quantified decision-making dynamics based on both choice and response time. Participants with lower levels of behavioral disadvantageous inequity (DI) aversion (reflected by a lower DDM weight for DI) showed stronger neural representations of DI in the dorsal anterior cingulate cortex (dACC). Functional connectivity analysis revealed a negative correlation between the dACC and bilateral ventrolateral prefrontal cortex (vlPFC) when DI was high. This connectivity predicted both rejection rates and response times associated with the acceptance of DI offers. Furthermore, robust linear regression showed that only dACC-vlPFC connectivity—not reward-related activity—explained both the rejection rates and response times. Finally, right vlPFC activity correlated with amygdala activity under high DI conditions. These findings suggest that the dACC plays a key role in regulating responses to DI, thereby facilitating the acceptance of unfair offers.议价是一种基本的社会行为，个体在此过程中往往会接受不公平的提议。传统行为模型仅基于选择数据构建，通常将此类接受行为解读为单纯的奖励最大化行为。然而，对不公平厌恶的调节可能在这些决策中同样发挥关键作用。将反应时与选择数据相结合，我们可以量化参与者在决定接受不公平提议时的内部心理努力。我们在参与者进行最后通牒博弈（ultimatum game）时开展了功能磁共振成像（functional magnetic resonance imaging, fMRI）扫描，要求他们在10秒内决定接受或拒绝提议者给出的金钱提议。我们借助漂移扩散模型（drift diffusion model, DDM），结合选择数据与反应时量化了决策动态。行为层面上，不利不公平待遇（disadvantageous inequity, DI）厌恶程度较低的参与者（表现为DDM对DI的权重更低），其背侧前扣带回皮层（dorsal anterior cingulate cortex, dACC）中DI的神经表征更强。功能连接分析显示，当DI水平较高时，dACC与双侧腹外侧前额叶皮层（ventrolateral prefrontal cortex, vlPFC）之间存在负相关关系。这种连接模式可以预测接受DI提议时的拒绝率与反应时。此外，稳健线性回归分析表明，唯有dACC-vlPFC连接——而非与奖励相关的神经活动——能够解释拒绝率与反应时的变化。最后，在高DI条件下，右侧vlPFC的活动与杏仁核（amygdala）活动呈显著相关。上述研究结果表明，dACC在调节个体对DI的反应中发挥关键作用，从而促进了个体对不公平提议的接受。