Tardiff Nathan, Graves Kathryn N, Thompson-Schill Sharon L
Department of Psychology, University of Pennsylvania Philadelphia, PA, United States.
Front Hum Neurosci. 2018 Dec 17;12:472. doi: 10.3389/fnhum.2018.00472. eCollection 2018.
Instructions have a powerful effect on learning and decision-making, biasing choice even in the face of disconfirming feedback. Detrimental biasing effects have been reported in a number of studies in which instruction was given prior to trial-and-error learning. Previous work has attributed individual differences in instructional bias to variations in prefrontal and striatal dopaminergic genes, suggesting a role for prefrontally-mediated cognitive control processes in biasing learning. The current study replicates and extends these findings. Human subjects performed a probabilistic reinforcement learning task after receiving inaccurate instructions about the quality of one of the options. In order to establish a causal relationship between prefrontal cortical mechanisms and instructional bias, we applied transcranial direct current stimulation over dorsolateral prefrontal cortex (anodal, cathodal, or sham) while subjects performed the task. We additionally genotyped subjects for the COMT Val158Met genetic polymorphism, which influences the breakdown of prefrontal dopamine, and for the DAT1/SLC6A3 variable number tandem repeat, which affects expression of striatal dopamine transporter. We replicated the finding that the COMT Met allele is associated with increased instructional bias and further demonstrated that variation in DAT1 has similar effects to variation in COMT, with 9-repeat carriers demonstrating increased bias relative to 10-repeat homozygotes. Consistent with increased top-down regulation of reinforcement learning, anodal subjects demonstrated greater bias relative to sham, though this effect was present only early in training. In contrast, there was no effect of cathodal stimulation. Finally, we fit computational models to subjects' data to better characterize the mechanisms underlying instruction bias. A novel choice bias model, in which instructions influence decision-making rather than learning, was found to best account for subjects' behavior. Overall, these data provide further evidence for the role of frontostriatal interactions in biasing instructed reinforcement learning, which adds to the growing literature documenting both costs and benefits of cognitive control.
指令对学习和决策有着强大的影响，即使面对与预期不符的反馈，也会使选择产生偏差。在一些先于试错学习给出指令的研究中，已报道了有害的偏差效应。先前的研究将指令偏差中的个体差异归因于前额叶和纹状体多巴胺能基因的变异，这表明前额叶介导的认知控制过程在偏差学习中发挥作用。本研究重复并扩展了这些发现。人类受试者在收到关于其中一个选项质量的不准确指令后，执行了概率强化学习任务。为了建立前额叶皮层机制与指令偏差之间的因果关系，我们在受试者执行任务时，对背外侧前额叶皮层施加经颅直流电刺激（阳极、阴极或假刺激）。我们还对受试者进行了COMT Val158Met基因多态性和DAT1/SLC6A3可变数目串联重复序列的基因分型，前者影响前额叶多巴胺的分解，后者影响纹状体多巴胺转运体的表达。我们重复了COMT Met等位基因与指令偏差增加相关的发现，并进一步证明DAT1的变异与COMT的变异有相似的效果，9重复携带者相对于10重复纯合子表现出更大的偏差。与强化学习中自上而下调节的增加一致，阳极刺激组相对于假刺激组表现出更大的偏差，尽管这种效应仅在训练早期出现。相比之下，阴极刺激没有效果。最后，我们将计算模型拟合到受试者的数据中，以更好地描述指令偏差背后的机制。一种新的选择偏差模型，即指令影响决策而非学习，被发现最能解释受试者的行为。总体而言，这些数据为额纹状体相互作用在偏差指导强化学习中的作用提供了进一步的证据，这也为记录认知控制的成本和收益的不断增长的文献增添了内容。
