Non-invasive transcranial stimulation of cerebellum and primary motor cortex (M1) has been shown to enhance motor learning. However, the mechanisms by which stimulation improves learning remain largely unknown. Here, we sought to shed light on the neural correlates of transcranial direct current stimulation (tDCS) during motor learning by simultaneously recording functional magnetic resonance imaging (fMRI). We found that right cerebellar tDCS, but not left M1 tDCS, led to enhanced sequence learning in the serial reaction time task. Performance was also improved following cerebellar tDCS compared to sham in a sequence production task, reflecting superior training effects persisting into the post-training period. These behavioral effects were accompanied by increased learning-specific activity in right M1, left cerebellum lobule VI, left inferior frontal gyrus and right inferior parietal lobule during cerebellar tDCS compared to sham. Despite the lack of group-level changes comparing left M1 tDCS to sham, activity increase in right M1, supplementary motor area, and bilateral middle frontal cortex, under M1 tDCS, was associated with better sequence performance. This suggests that lack of group effects in M1 tDCS relate to inter-individual variability in learning-related activation patterns. We further investigated how tDCS modulates effective connectivity in the cortico-striato-cerebellar learning network. Using dynamic causal modelling, we found altered connectivity patterns during both M1 and cerebellar tDCS when compared to sham. Specifically, during cerebellar tDCS, negative modulation of a connection from putamen to cerebellum was decreased for sequence learning only, effectively leading to decreased inhibition of the cerebellum. These results show specific effects of cerebellar tDCS on functional activity and connectivity in the motor learning network and may facilitate the optimization of motor rehabilitation involving cerebellar non-invasive stimulation.

中文翻译：

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小脑 tDCS 对运动学习的有益影响与壳 - 小脑连接的改变有关：同时进行的 tDCS-fMRI 研究

小脑和初级运动皮层 (M1) 的非侵入性经颅刺激已被证明可以增强运动学习。然而，刺激改善学习的机制在很大程度上仍然未知。在这里，我们试图通过同时记录功能磁共振成像 (fMRI) 来阐明运动学习过程中经颅直流电刺激 (tDCS) 的神经相关性。我们发现右侧小脑 tDCS，而不是左侧 M1 tDCS，导致序列反应时间任务中序列学习的增强。与序列生产任务中的假手术相比，小脑 tDCS 后的表现也得到了改善，反映了持续到训练后时期的卓越训练效果。这些行为影响伴随着右侧 M1、左侧小脑小叶 VI、与假手术相比，小脑 tDCS 期间左侧额下回和右侧顶下小叶。尽管左侧 M1 tDCS 与假手术相比缺乏组级变化，但在 M1 tDCS 下，右侧 M1、辅助运动区和双侧中额叶皮层的活动增加与更好的序列性能相关。这表明 M1 tDCS 中缺乏群体效应与学习相关激活模式的个体间差异有关。我们进一步研究了 tDCS 如何调节皮质-纹状体-小脑学习网络中的有效连接。使用动态因果建模，我们发现与假手术相比，M1 和小脑 tDCS 期间的连接模式发生了改变。具体来说，在小脑 tDCS 期间，从壳核到小脑的连接的负调制仅在序列学习中减少，有效地导致小脑抑制的减少。这些结果显示了小脑 tDCS 对运动学习网络中的功能活动和连通性的特定影响，并且可能有助于优化涉及小脑无创刺激的运动康复。