Applying a weak electrical current to the cortex has the potential to modulate neural functioning and behaviour. The most common stimulation technique, transcranial direct current stimulation (tDCS), has been used for causal investigations of brain and cognitive functioning, and to treat psychiatric conditions such as depression. However, the efficacy of tDCS in modulating behaviour varies across individuals. Moreover, despite being associated with different neural effects, the two polarities of electrical stimulation – anodal and cathodal – can result in similar behavioural outcomes. Here we employed a previously replicated behavioural paradigm that has been associated with polarity non-specific disruption of training effects in a simple decision-making task. We then used the linear ballistic accumulator model to quantify latent components of the decision-making task. In addition, magnetic resonance imaging measures were acquired prior to tDCS sessions to quantify cortical morphology and local neurochemical concentrations. Both anodal and cathodal stimulation disrupted learning-related task improvement relative to sham (placebo) stimulation, but the two polarities of stimulation had distinct effects on latent task components. Whereas anodal stimulation tended to affect decision thresholds for the behavioural task, cathodal stimulation altered evidence accumulation rates. Moreover, performance variability with anodal stimulation was related to cortical thickness of the inferior frontal gyrus, whereas performance variability with cathodal stimulation was related to cortical thickness in the inferior precentral sulcus, as well as to prefrontal neurochemical excitability. Our findings demonstrate that both cortical morphology and local neurochemical balance are important determinants of individual differences in behavioural responses to electrical brain stimulation.

向皮层施加微弱的电流可能会调节神经功能和行为。最常见的刺激技术是经颅直流电刺激（tDCS），已用于脑和认知功能的因果研究，并用于治疗诸如抑郁症等精神疾病。但是，tDCS调节行为的功效因人而异。此外，尽管受到不同的神经作用，但电刺激的两个极性（阳极和阴极）可以导致相似的行为结果。在这里，我们采用了先前复制的行为范式，该行为范式已与简单决策过程中的训练效果的极性非特异性中断相关联。然后，我们使用线性弹道累加器模型来量化决策任务的潜在组成部分。此外，在tDCS会议之前需要磁共振成像测量，以量化皮层形态和局部神经化学浓度。相对于假（安慰剂）刺激，阳极刺激和阴极刺激均干扰了与学习有关的任务改善，但刺激的两种极性对潜伏任务成分具有明显影响。阳极刺激往往会影响行为任务的决策阈值，而阴极刺激会改变证据积累率。此外，阳极刺激的性能差异与额下回的皮层厚度有关，阴极刺激下的性能变化与下中央前沟皮质厚度以及前额叶神经化学兴奋性有关。我们的发现表明，皮质形态学和局部神经化学平衡都是对电刺激行为反应个体差异的重要决定因素。