BACKGROUND Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that has shown promise for rehabilitation after stroke. Ipsilesional anodal tDCS (a-tDCS) over the motor cortex increases corticospinal excitability, while contralesional cathodal tDCS (c-tDCS) restores interhemispheric balance, both resulting in offline improved reaction times of delayed voluntary upper-extremity movements. We aimed to investigate whether tDCS would also have a beneficial effect on delayed leg motor responses after stroke. In addition, we identified whether variability in tDCS effects was associated with the level of leg motor function. METHODS In a cross-over design, 13 people with chronic stroke completed three 15-min sessions of anodal, cathodal and sham stimulation over the primary motor cortex on separate days in an order balanced across participants. Directly after stimulation, participants performed a comprehensive set of lower-extremity tasks involving the paretic tibialis anterior (TA): voluntary ankle-dorsiflexion, gait initiation, and backward balance perturbation. For all tasks, TA onset latencies were determined. In addition, leg motor function was determined by the Fugl-Meyer Assessment - leg score (FMA-L). Repeated measures ANOVA was used to reveal tDCS effects on reaction times. Pearson correlation coefficients were used to establish the relation between tDCS effects and leg motor function. RESULTS For all tasks, TA reaction times did not differ across tDCS sessions. For gait initiation and backward balance perturbation, differences between sham and active stimulation (a-tDCS or c-tDCS) did not correlate with leg motor function. Yet, for ankle dorsiflexion, individual reaction time differences between c-tDCS and sham were strongly associated with FMA-L, with more severely impaired patients exhibiting slower paretic reaction times following c-tDCS. CONCLUSION We found no evidence for offline tDCS-induced benefits. Interestingly, we found that c-tDCS may have unfavorable effects on voluntary control of the paretic leg in severely impaired patients with chronic stroke. This finding points at potential vicarious control from the unaffected hemisphere to the paretic leg. The absence of tDCS-induced effects on gait and balance, two functionally relevant tasks, shows that such motor behavior is inadequately stimulated by currently used tDCS applications. TRIAL REGISTRATION The study is registered in the Netherlands Trial Register (NL5684; April 13th, 2016).

中文翻译：

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经颅直流电刺激对中风后人下肢运动反应时间的离线影响：一项交叉试验研究。

背景技术经颅直流电刺激（tDCS）是一种无创性脑刺激技术，已经显示出中风后康复的希望。运动皮层上的同侧肛门tDCS（a-tDCS）增加了皮质脊髓的兴奋性，而对侧阴极tDCS（c-tDCS）恢复了半球之间的平衡，两者都导致离线的主动上肢延迟运动的反应时间缩短了。我们旨在研究tDCS是否也会对卒中后延迟的腿部运动反应产生有益的影响。此外，我们确定tDCS效应的变异性是否与腿部运动功能水平相关。方法在一项交叉设计中，有13位慢性卒中患者完成了三个15分钟的阳极麻醉，在不同的天数中，对原发性运动皮层的阴极和假刺激刺激的顺序要在参与者之间保持平衡。刺激后，参与者立即执行一系列下肢综合任务，涉及胫骨前胫骨（TA）：自愿性踝背屈，步态起始和向后平衡扰动。对于所有任务，确定了TA发作潜伏期。另外，腿运动功能由Fugl-Meyer评估-腿得分（FMA-L）确定。重复测量使用方差分析（ANOVA）揭示tDCS对反应时间的影响。皮尔逊相关系数用于建立tDCS效应与腿部运动功能之间的关系。结果对于所有任务，TA响应时间在tDCS会话之间没有差异。为了步态启动和向后平衡扰动，假手术和主动刺激（a-tDCS或c-tDCS）之间的差异与腿部运动功能无关。然而，对于脚踝背屈，c-tDCS与假手术之间的个体反应时间差异与FMA-L密切相关，更严重受损的患者在c-tDCS之后表现出较慢的paretic反应时间。结论我们发现没有证据表明脱机tDCS可以带来收益。有趣的是，我们发现c-tDCS对严重受损的慢性卒中患者的小腿自主控制可能有不利影响。这一发现指出了从未受影响的半球到腹足的潜在替代控制。tDCS对步态和平衡的影响（两个功能相关的任务）的缺失表明，当前使用的tDCS应用不能充分激发这种运动行为。