Abellaneda-Pérez Kilian, Vaqué-Alcázar Lídia, Perellón-Alfonso Ruben, Bargalló Núria, Kuo Min-Fang, Pascual-Leone Alvaro, Nitsche Michael A, Bartrés-Faz David
Department of Medicine, Faculty of Medicine and Health Sciences, Institute of Neurosciences, University of Barcelona, Barcelona, Spain.
Institute of Biomedical Research August Pi i Sunyer, Barcelona, Spain.
Front Neurosci. 2020 Jan 17;13:1440. doi: 10.3389/fnins.2019.01440. eCollection 2019.
Transcranial direct and alternating current stimulation (tDCS and tACS, respectively) entail capability to modulate human brain dynamics and cognition. However, the comparability of these approaches at the level of large-scale functional networks has not been thoroughly investigated. In this study, 44 subjects were randomly assigned to receive sham ( = 15), tDCS ( = 15), or tACS ( = 14). The first electrode (anode in tDCS) was positioned over the left dorsolateral prefrontal cortex, the target area, and the second electrode (cathode in tDCS) was placed over the right supraorbital region. tDCS was delivered with a constant current of 2 mA. tACS was fixed to 2 mA peak-to-peak with 6 Hz frequency. Stimulation was applied concurrently with functional magnetic resonance imaging (fMRI) acquisitions, both at rest and during the performance of a verbal working memory (WM) task. After stimulation, subjects repeated the fMRI WM task. Our results indicated that at rest, tDCS increased functional connectivity particularly within the default-mode network (DMN), while tACS decreased it. When comparing both fMRI WM tasks, it was observed that tDCS displayed decreased brain activity post-stimulation as compared to online. Conversely, tACS effects were driven by neural increases online as compared to post-stimulation. Interestingly, both effects primarily occurred within DMN-related areas. Regarding the differences in each fMRI WM task, during the online fMRI WM task, tACS engaged distributed neural resources which did not overlap with the WM-dependent activity pattern, but with some posterior DMN regions. In contrast, during the post-stimulation fMRI WM task, tDCS strengthened prefrontal DMN deactivations, being these activity reductions associated with faster responses. Furthermore, it was observed that tDCS neural responses presented certain consistency across distinct fMRI modalities, while tACS did not. In sum, tDCS and tACS modulate fMRI-derived network dynamics differently. However, both effects seem to focus on DMN regions and the WM network-DMN shift, which are highly affected in aging and disease. Thus, albeit exploratory and needing further replication with larger samples, our results might provide a refined understanding of how the DMN functioning can be externally modulated through commonly used non-invasive brain stimulation techniques, which may be of eventual clinical relevance.
经颅直流电刺激和经颅交流电刺激（分别为tDCS和tACS）具有调节人类脑动力学和认知的能力。然而，这些方法在大规模功能网络层面的可比性尚未得到充分研究。在本研究中，44名受试者被随机分配接受假刺激（n = 15）、tDCS（n = 15）或tACS（n = 14）。第一个电极（tDCS中的阳极）置于目标区域左侧背外侧前额叶皮质上方，第二个电极（tDCS中的阴极）置于右侧眶上区域。tDCS以2 mA的恒定电流施加。tACS固定为峰峰值2 mA，频率为6 Hz。在静息状态和执行言语工作记忆（WM）任务期间，刺激与功能磁共振成像（fMRI）采集同时进行。刺激后，受试者重复fMRI WM任务。我们的结果表明，在静息状态下，tDCS增加了功能连接性，特别是在默认模式网络（DMN）内，而tACS则降低了功能连接性。在比较两个fMRI WM任务时，观察到与联机阶段相比，tDCS在刺激后显示出脑活动降低。相反，与刺激后相比，tACS的效应是由联机阶段的神经活动增加驱动的。有趣的是，这两种效应主要发生在与DMN相关的区域。关于每个fMRI WM任务中的差异，在联机fMRI WM任务期间，tACS激活了分布式神经资源，这些资源与依赖WM的活动模式不重叠，但与一些后DMN区域重叠。相比之下，在刺激后的fMRI WM任务期间，tDCS增强了前额叶DMN的失活，这些活动减少与更快的反应相关。此外，观察到tDCS的神经反应在不同的fMRI模式下呈现出一定的一致性，而tACS则没有。总之，tDCS和tACS对fMRI衍生的网络动力学有不同的调节作用。然而，这两种效应似乎都集中在DMN区域和WM网络 - DMN的转变上，而这在衰老和疾病中受到高度影响。因此，尽管本研究具有探索性且需要更大样本进一步重复验证，但我们的结果可能会使人们对如何通过常用的非侵入性脑刺激技术从外部调节DMN功能有更精确的理解，这最终可能具有临床相关性。
