Dopamine is implicated in signalling model-free (MF) reward prediction errors and various aspects of model-based (MB) credit assignment and choice. Recently, we showed that cooperative interactions between MB and MF systems include guidance of MF credit assignment by MB inference. Here, we used a double-blind, placebo-controlled, within-subjects design to test the hypothesis that enhancing dopamine levels, using levodopa, boosts the guidance of MF credit assignment by MB inference. We found that levodopa enhanced retrospective guidance of MF credit assignment by MB inference, without impacting on MF and MB influences per se. This drug effect positively correlated with working memory, but only in a context where reward needed to be recalled for MF credit assignment. The dopaminergic enhancement in MB-MF interactions correlated negatively with a dopamine-dependent change in MB credit assignment, possibly reflecting a potential trade-off between these two components of behavioural control. Thus, our findings demonstrate that dopamine boosts MB inference during guidance of MF learning, supported in part by working memory, but trading-off with a dopaminergic enhancement of MB credit assignment. The findings highlight a novel role for a DA influence on MB-MF interactions.

中文翻译：

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多巴胺通过促进回顾性基于模型的推理来增强无模型信用分配

多巴胺与无模型（MF）奖励预测错误以及基于模型的（MB）信用分配和选择的各个方面有关。最近，我们证明了MB和MF系统之间的协作交互包括MB推理对MF信用分配的指导。在这里，我们使用了双盲，安慰剂对照的受试者内部设计来检验以下假设，即使用左旋多巴提高多巴胺水平可以通过MB推理来提高MF信用分配的指导。我们发现左旋多巴通过MB推理增强了MF信用分配的追溯指导，而不会影响MF和MB本身。这种药物作用与工作记忆成正相关，但仅在需要为MF信用分配调回奖励的情况下。MB-MF相互作用中的多巴胺能增强与MB信用分配中的多巴胺依赖性变化负相关，这可能反映了行为控制的这两个组成部分之间的潜在权衡。因此，我们的研究结果表明，多巴胺在MF学习指导过程中提高了MB推理能力，部分由工作记忆支持，但在多巴胺能提高MB学分分配方面进行了权衡。这些发现凸显了DA对MB-MF相互作用的新作用。