Moral behavior requires learning how our actions help or harm others. Theoretical accounts of learning propose a key division between “model-free” algorithms that cache outcome values in actions and “model-based” algorithms that map actions to outcomes. Here, we tested the engagement of these mechanisms and their neural basis as participants learned to avoid painful electric shocks for themselves and a stranger. We found that model-free decision making was prioritized when learning to avoid harming others compared to oneself. Model-free prediction errors for others relative to self were tracked in the thalamus/caudate. At the time of choice, neural activity consistent with model-free moral learning was observed in subgenual anterior cingulate cortex (sgACC), and switching after harming others was associated with stronger connectivity between sgACC and dorsolateral prefrontal cortex. Finally, model-free moral learning varied with individual differences in moral judgment. Our findings suggest moral learning favors efficiency over flexibility and is underpinned by specific neural mechanisms.

道德行为需要了解我们的行为如何帮助或伤害他人。学习的理论解释提出了在动作中缓存结果值的“无模型”算法和将动作映射到结果的“基于模型”算法之间的关键划分。在这里，我们测试了这些机制的参与及其神经基础，因为参与者学会了避免对自己和陌生人造成痛苦的电击。我们发现，在学习避免伤害他人而不是伤害自己时，无模型决策被优先考虑。在丘脑/尾状核中跟踪其他人相对于自己的无模型预测误差。在选择时，在膝下前扣带皮层 (sgACC) 中观察到与无模型道德学习一致的神经活动，伤害他人后的转换与 sgACC 和背外侧前额叶皮层之间更强的连接性有关。最后，无模型的道德学习随着道德判断的个体差异而变化。我们的研究结果表明，道德学习有利于效率而不是灵活性，并以特定的神经机制为基础。