Wang Huijun, Wei Kunlin
School of Psychological and Cognitive Sciences and Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing 100871, China.
Key Laboratory of Machine Perception (Ministry of Education), Peking University, Beijing 100871, China.
Brain Sci. 2022 Sep 29;12(10):1325. doi: 10.3390/brainsci12101325.
Humans constantly calibrate their sensorimotor system to accommodate environmental changes, and this perception-action integration is extensively studied using sensorimotor adaptation paradigms. The cerebellum is one of the key brain regions for sensorimotor adaptation, but previous attempts to modulate sensorimotor adaptation with cerebellar transcranial direct current stimulation (ctDCS) produced inconsistent findings. Since both conscious/explicit learning and procedural/implicit learning are involved in adaptation, researchers have proposed that ctDCS only affects sensorimotor adaptation when implicit learning dominates the overall adaptation. However, previous research had both types of learning co-exist in their experiments without controlling their potential interaction under the influence of ctDCS. Here, we used error clamp perturbation and gradual perturbation, two effective techniques to elicit implicit learning only, to test the ctDCS effect on sensorimotor adaptation. We administrated ctDCS to independent groups of participants while they implicitly adapted to visual errors. In Experiment 1, we found that cerebellar anodal tDCS had no effect on implicit adaptation induced by error clamp. In Experiment 2, we applied both anodal and cathodal stimulation and used a smaller error clamp to prevent a potential ceiling effect, and replicated the null effect. In Experiment 3, we used gradually imposed visual errors to elicit implicit adaptation but still found no effect of anodal tDCS. With a total of 174 participants, we conclude that the previous inconsistent tDCS effect on sensorimotor adaptation cannot be explained by the relative contribution of implicit learning. Given that the cerebellum is simultaneously involved in explicit and implicit learning, our results suggest that the complex interplay between the two learning processes and large individual differences associated with this interplay might contribute to the inconsistent findings from previous studies on ctDCS and sensorimotor adaptation.
人类不断校准其感觉运动系统以适应环境变化，并且这种感知 - 行动整合通过感觉运动适应范式得到了广泛研究。小脑是感觉运动适应的关键脑区之一，但先前尝试用小脑经颅直流电刺激（ctDCS）调节感觉运动适应的研究结果并不一致。由于意识/显性学习和程序/隐性学习都参与了适应过程，研究人员提出，只有当隐性学习在整体适应中占主导地位时，ctDCS才会影响感觉运动适应。然而，先前的研究在实验中让两种类型的学习同时存在，却没有在ctDCS的影响下控制它们潜在的相互作用。在这里，我们使用误差钳位扰动和渐进扰动这两种仅引发隐性学习的有效技术，来测试ctDCS对感觉运动适应的影响。我们在参与者隐性适应视觉误差时对独立组施加ctDCS。在实验1中，我们发现小脑阳极性tDCS对误差钳位诱导的隐性适应没有影响。在实验2中，我们同时应用了阳极和阴极刺激，并使用较小的误差钳位来防止潜在的天花板效应，结果再次验证了无效效应。在实验3中，我们使用逐渐施加的视觉误差来引发隐性适应，但仍然没有发现阳极tDCS的作用。通过总共174名参与者，我们得出结论，先前关于tDCS对感觉运动适应的不一致效应不能用隐性学习的相对贡献来解释。鉴于小脑同时参与显性和隐性学习，我们的结果表明，这两种学习过程之间的复杂相互作用以及与这种相互作用相关的个体差异可能导致了先前关于ctDCS和感觉运动适应研究结果的不一致。
