Antonenko Daria, Schubert Florian, Bohm Florian, Ittermann Bernd, Aydin Semiha, Hayek Dayana, Grittner Ulrike, Flöel Agnes
Department of Neurology, NeuroCure Clinical Research Center, Charité Universitätsmedizin, 10117 Berlin, Germany,
Physikalisch-Technische Bundesanstalt (PTB), 10587 Berlin, Germany.
J Neurosci. 2017 Apr 12;37(15):4065-4073. doi: 10.1523/JNEUROSCI.0079-17.2017. Epub 2017 Mar 17.
Transcranial direct current stimulation (tDCS) modulates human behavior, neuronal patterns, and metabolite concentrations, with exciting potential for neurorehabilitation. However, the understanding of tDCS-induced alterations on the neuronal level is incomplete, and conclusions from young adults, in whom the majority of studies have been conducted, cannot be easily transferred to older populations. Here, we investigated tDCS-induced effects in older adults ( = 48; age range, 50-79 years) using magnetic resonance spectroscopy to quantify GABA levels as well as resting-state functional magnetic resonance imaging to assess sensorimotor network strength and interhemispheric connectivity. In a randomized, counterbalanced, crossover design, we applied anodal tDCS (atDCS), cathodal tDCS (ctDCS), and sham tDCS (stDCS) over the left sensorimotor region. We observed a significant reduction of GABA levels after atDCS compared with stDCS, reflecting the preserved neuromodulatory effect of atDCS in older adults. Moreover, resting-state functional coupling was decreased during atDCS compared with stDCS, most likely indicating augmented efficiency in brain network functioning. Increased levels of interhemispheric connectivity with age were diminished by atDCS, suggesting stimulation-induced functional decoupling. Further, the magnitude of atDCS-induced local plasticity was related to baseline functional network strength. Our findings provide novel insight into the neuronal correlates underlying tDCS-induced neuronal plasticity in older adults and thus might help to develop tDCS interventions tailored to the aging brain. Transcranial direct current stimulation (tDCS) modulates human behavior, neuronal patterns, and metabolite concentrations, with exciting potential for neurorehabilitation. However, the understanding of tDCS-induced alterations on the neuronal level is incomplete, and conclusions from young adults cannot be easily transferred to older populations. We used a systematic multimodal imaging approach to investigate the neurophysiological effects of tDCS in older adults and found stimulation-induced effects on GABA levels, reflecting augmented local plasticity and functional connectivity, suggesting modulation of network efficiency. Our findings may help to reconcile some of the recent reports on the variability of tDCS-induced effects, not only implicating age as a crucial modulating factor, but detailing its specific impact on the functionality of neural networks.
经颅直流电刺激（tDCS）可调节人类行为、神经元活动模式和代谢物浓度，在神经康复方面具有令人兴奋的潜力。然而，目前对tDCS在神经元水平上所引起变化的理解并不完整，而且大多数相关研究都是在年轻人中进行的，其结论难以直接推广至老年人群体。在此，我们对48名年龄在50至79岁之间的老年人进行研究，采用磁共振波谱法量化γ-氨基丁酸（GABA）水平，并利用静息态功能磁共振成像评估感觉运动网络强度和半球间连接性，以此来探究tDCS对老年人的影响。在一项随机、平衡、交叉设计中，我们对左侧感觉运动区施加阳极tDCS（atDCS）、阴极tDCS（ctDCS）和伪刺激tDCS（stDCS）。我们观察到，与伪刺激相比，阳极tDCS后GABA水平显著降低，这反映出阳极tDCS在老年人中保留了神经调节作用。此外，与伪刺激相比，阳极tDCS期间静息态功能耦合降低，这很可能表明大脑网络功能效率提高。随着年龄增长而增加的半球间连接水平在阳极tDCS作用下降低，这表明刺激诱导了功能去耦联。此外，阳极tDCS诱导的局部可塑性程度与基线功能网络强度相关。我们的研究结果为老年人中tDCS诱导神经元可塑性的潜在神经机制提供了新的见解，因此可能有助于开发针对衰老大脑的tDCS干预措施。经颅直流电刺激（tDCS）可调节人类行为、神经元活动模式和代谢物浓度，在神经康复方面具有令人兴奋的潜力。然而，目前对tDCS在神经元水平上所引起变化的理解并不完整，年轻人的研究结论难以直接推广至老年人群体。我们采用系统的多模态成像方法来研究tDCS对老年人的神经生理影响，发现刺激对GABA水平有影响，这反映出局部可塑性增强和功能连接性增强，表明网络效率受到了调节。我们的研究结果可能有助于调和最近一些关于tDCS诱导效应变异性的报道，不仅表明年龄是一个关键的调节因素，还详细说明了其对神经网络功能的具体影响。
