Significance: Combining transcranial direct-current stimulation (tDCS) with functional near-infrared spectroscopy (fNIRS) is a recent approach to exploring brain activation evoked by neurostimulation. Aim: To critically evaluate studies combining tDCS and fNIRS and provide a consolidated overview of cortical hemodynamic responses to neurostimulation. Approach: Key terms were searched in three databases (MEDLINE, EMBASE, and PsycINFO) with cross-referencing and works from Google Scholar also evaluated. All studies reporting on fNIRS-derived hemoglobin changes evoked by tDCS were included. Results: Literature searches revealed 474 articles, of which 28 were included for final review (22 in healthy individuals: 9 involving rest and 13 with tasks; 6 in the clinical setting). At rest, an overall increase in cortical activation was observed in fNIRS responses at the site of stimulation, with evidence suggesting nonstimulated brain regions are also similarly affected. Conversely, during tasks, reduced cortical activation was observed during online stimulation. Offline and poststimulation effects were less consistent, as is the impact on clinical populations and their symptom correlation. Conclusion: This review explores the methodological frameworks for fNIRS-tDCS evaluations and summarizes hemodynamic responses associated with tDCS in all populations. Our findings provide further evidence of the impact of tDCS on neuronal activation within functionally connected networks.

中文翻译：

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结合功能近红外光谱和经颅直流电刺激研究的系统评价。

意义：结合经颅直流电刺激（tDCS）和功能性近红外光谱（fNIRS）是探索神经刺激引起的大脑激活的最新方法。目的：严格评估tDCS和fNIRS结合的研究，并提供对神经刺激的皮质血液动力学反应的综合综述。方法：在具有交叉引用的三个数据库（MEDLINE，EMBASE和PsycINFO）中搜索关键术语，并对Google Scholar的著作进行了评估。包括所有有关tDCS引起的fNIRS衍生的血红蛋白变化的报告。结果：文献检索发现474篇文章，其中28篇被纳入最终审查（健康人22篇：9篇涉及休息，13篇有任务；在临床中6篇）。在休息，在刺激部位的fNIRS反应中观察到皮质激活的总体增加，证据表明未刺激的大脑区域也受到类似的影响。相反，在任务过程中，在线刺激过程中观察到皮质激活减少。脱机和刺激后效果不太一致，对临床人群及其症状相关性的影响也是如此。结论：本综述探讨了fNIRS-tDCS评估的方法学框架，并总结了所有人群中与tDCS相关的血液动力学反应。我们的发现为功能连接网络中tDCS对神经元激活的影响提供了进一步的证据。在线刺激过程中观察到皮质激活减少。脱机和刺激后效果不太一致，对临床人群及其症状相关性的影响也不太一致。结论：本综述探讨了fNIRS-tDCS评估的方法学框架，并总结了所有人群中与tDCS相关的血液动力学反应。我们的发现为功能连接网络中tDCS对神经元激活的影响提供了进一步的证据。在线刺激过程中观察到皮质激活减少。脱机和刺激后效果不太一致，对临床人群及其症状相关性的影响也是如此。结论：本综述探讨了fNIRS-tDCS评估的方法学框架，并总结了所有人群中与tDCS相关的血液动力学反应。我们的发现为功能连接网络中tDCS对神经元激活的影响提供了进一步的证据。