BACKGROUND Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that has the potential to induce motor cortical plasticity in humans. It is well known that motor cortical plasticity plays an essential role in motor learning and recovery in patients with stroke and neurodegenerative disorders. However, it remains unclear how cognitive function influences motor cortical plasticity induced by tDCS. The present study aimed to investigate whether anodal tDCS combined with attention to a target muscle could enhance motor cortical plasticity and improve motor learning in healthy individuals. METHODS Thirty-three healthy volunteers were assigned to two experiments. In experiment 1, there were three interventional conditions: 1) anodal tDCS was applied while participants paid attention to the first dorsal interosseous (FDI) muscle, 2) anodal tDCS was applied while participants paid attention to the sound, and 3) anodal tDCS was applied without the participants paying attention to the FDI muscle or the sound. Anodal tDCS (2 mA, 10 min) was applied over the primary motor cortex (M1). Changes in motor evoked potentials (MEPs), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF) were assessed before and immediately after (0 min), and then 10 min, 30 min, and 60 min after each intervention. In experiment 2, we investigated whether the combination of anodal tDCS and attention to the abductor pollicis brevis (APB) muscle could facilitate the learning of a ballistic thumb movement. RESULTS Anodal tDCS increased cortical excitability in all conditions immediately after the stimulation. Significant increases in MEPs and significant decreases in SICI were observed for at least 60 min after anodal tDCS, but only when participants paid attention to the FDI muscle. In contrast, no significant changes in ICF were observed in any condition. In experiment 2, the combination of tDCS and attention to the APB muscle significantly enhanced the acquisition of a ballistic thumb movement. The higher performance was still observed 7 days after the stimulation. CONCLUSIONS This study shows that anodal tDCS over M1 in conjunction with attention to the target muscle enhances motor cortex plasticity and improves motor learning in healthy adults. These findings suggest that a combination of attention and tDCS may be an effective strategy to promote rehabilitation training in patients with stroke and neurodegenerative disorders. TRIAL REGISTRATION Retrospectively registered (UMIN000036848).

中文翻译：

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经颅直流电刺激与注意相结合可增加健康志愿者的皮层兴奋性并改善运动学习。

背景技术经颅直流电刺激（tDCS）是一种非侵入性的脑刺激技术，其具有诱导人类运动皮层可塑性的潜力。众所周知，运动性皮质可塑性在中风和神经退行性疾病患者的运动学习和恢复中起着至关重要的作用。但是，尚不清楚认知功能如何影响tDCS诱导的运动皮质可塑性。本研究旨在调查阳极tDCS结合对目标肌肉的注意是否可以增强健康个体的运动皮层可塑性并改善运动学习。方法33名健康志愿者被分配到两个实验中。在实验1中，存在三种介入条件：1）在参加者注意第一背骨间（FDI）肌肉时应用了阳极tDCS，2）在参加者注意声音的同时应用了阳极tDCS，并且3）在没有参加者注意FDI肌肉的情况下应用了阳极tDCS或声音。阳极tDCS（2 mA，10分钟）施加在初级运动皮层（M1）上。在每次干预之前和之后（0分钟），以及之后10分钟，30分钟和60分钟之后，分别评估运动诱发电位（MEP），短间隔皮质内抑制（SICI）和皮质内促进（ICF）的变化。在实验2中，我们研究了阳极tDCS的结合以及对外展肌短缩肌（APB）肌肉的注意是否可以促进拇指弹道运动的学习。结果刺激后，在所有情况下，阳极tDCS均可增加皮质兴奋性。在阳极tDCS后至少60分钟内，观察到MEP的显着增加和SICI的显着降低，但仅当参与者注意FDI肌肉时才观察到。相反，在任何情况下均未观察到ICF的显着变化。在实验2中，tDCS和对APB肌肉的注意力的结合显着增强了弹道拇指运动的获得。刺激后7天仍观察到较高的性能。结论这项研究表明，在健康成年人中，超过M1的阳极tDCS结合对目标肌肉的注意增强了运动皮层的可塑性并改善了运动学习。这些发现表明，注意力和tDCS的结合可能是促进中风和神经退行性疾病患者康复训练的有效策略。试用注册追溯注册（UMIN000036848）。