Background

Transcranial direct current stimulation (tDCS) is a form of noninvasive brain stimulation whose potential as a cognitive therapy is hindered by our limited understanding of how participant and experimental factors influence its effects. Using functional MRI to study brain networks, we have previously shown in healthy controls that the physiological effects of tDCS are strongly influenced by brain state. We have additionally shown, in both healthy and traumatic brain injury (TBI) populations, that the behavioral effects of tDCS are positively correlated with white matter (WM) structure.

Objectives

In this study we investigate how these two factors, WM structure and brain state, interact to shape the effect of tDCS on brain network activity.

Methods

We applied anodal, cathodal and sham tDCS to the right inferior frontal gyrus (rIFG) of healthy (n = 22) and TBI participants (n = 34). We used the Choice Reaction Task (CRT) performance to manipulate brain state during tDCS. We acquired simultaneous fMRI to assess activity of cognitive brain networks and used Fractional Anisotropy (FA) as a measure of WM structure.

Results

We find that the effects of tDCS on brain network activity in TBI participants are highly dependent on brain state, replicating findings from our previous healthy control study in a separate, patient cohort. We then show that WM structure further modulates the brain-state dependent effects of tDCS on brain network activity. These effects are not unidirectional - in the absence of task with anodal and cathodal tDCS, FA is positively correlated with brain activity in several regions of the default mode network. Conversely, with cathodal tDCS during CRT performance, FA is negatively correlated with brain activity in a salience network region.

Conclusions

Our results show that experimental and participant factors interact to have unexpected effects on brain network activity, and that these effects are not fully predictable by studying the factors in isolation.

中文翻译：

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研究白质和大脑状态对 tDCS 诱导的大脑网络活动变化的相互作用

背景

经颅直流电刺激 (tDCS) 是一种非侵入性脑刺激形式，其作为认知疗法的潜力受到我们对参与者和实验因素如何影响其影响的有限理解的阻碍。使用功能性 MRI 研究大脑网络，我们之前已经在健康对照中表明 tDCS 的生理效应受到大脑状态的强烈影响。我们还表明，在健康和创伤性脑损伤 (TBI) 人群中，tDCS 的行为影响与白质 (WM) 结构呈正相关。

目标

在这项研究中，我们研究了 WM 结构和大脑状态这两个因素如何相互作用以塑造 tDCS 对大脑网络活动的影响。

方法

我们将阳极、阴极和假 tDCS 应用于健康 (n = 22) 和 TBI 参与者 (n = 34) 的右侧额下回 (rIFG)。我们使用选择反应任务 (CRT) 性能来操纵 tDCS 期间的大脑状态。我们获得了同步 fMRI 来评估认知大脑网络的活动，并使用分数各向异性 (FA) 作为 WM 结构的衡量标准。

结果

我们发现 tDCS 对 TBI 参与者大脑网络活动的影响高度依赖于大脑状态，在单独的患者队列中复制了我们之前的健康对照研究的结果。然后，我们表明 WM 结构进一步调节了 tDCS 对大脑网络活动的大脑状态依赖性影响。这些影响不是单向的——在没有阳极和阴极 tDCS 任务的情况下，FA 与默认模式网络的几个区域中的大脑活动呈正相关。相反，在 CRT 性能期间使用阴极 tDCS，FA 与显着网络区域中的大脑活动呈负相关。

结论

我们的结果表明，实验因素和参与者因素相互作用会对大脑网络活动产生意想不到的影响，并且这些影响不能通过单独研究这些因素来完全预测。