Department of Neurology, University of California-San Francisco, San Francisco, CA, USA; Neuroscape, University of California-San Francisco, San Francisco, CA, USA.
Department of Neurology, University of California-San Francisco, San Francisco, CA, USA; Neuroscape, University of California-San Francisco, San Francisco, CA, USA.
Brain Stimul. 2021 Sep-Oct;14(5):1317-1329. doi: 10.1016/j.brs.2021.08.017. Epub 2021 Sep 1.
Noninvasive transcranial electrical stimulation (tES) research has been plagued with inconsistent effects. Recent work has suggested neuroanatomical and neurophysiological variability may alter tES efficacy. However, direct evidence is limited.
We have previously replicated effects of transcranial alternating current stimulation (tACS) on improving multitasking ability in young adults. Here, we attempt to assess whether these stimulation parameters have comparable effects in older adults (aged 60-80 years), which is a population known to have greater variability in neuroanatomy and neurophysiology. It is hypothesized that this variability in neuroanatomy and neurophysiology will be predictive of tACS efficacy.
We conducted a pre-registered study where tACS was applied above the prefrontal cortex (between electrodes F3-F4) while participants were engaged in multitasking. Participants were randomized to receive either 6-Hz (theta) tACS for 26.67 min daily for three days (80 min total; Long Exposure Theta group), 6-Hz tACS for 5.33 min daily (16-min total; Short Exposure Theta group), or 1-Hz tACS for 26.67 min (80 min total; Control group). To account for neuroanatomy, magnetic resonance imaging data was used to form individualized models of the tACS-induced electric field (EF) within the brain. To account for neurophysiology, electroencephalography data was used to identify individual peak theta frequency.
Results indicated that only in the Long Theta group, performance change was correlated with modeled EF and peak theta frequency. Together, modeled EF and peak theta frequency accounted for 54%-65% of the variance in tACS-related performance improvements, which sustained for a month.
These results demonstrate the importance of individual differences in neuroanatomy and neurophysiology in tACS research and help account for inconsistent effects across studies.
非侵入性经颅电刺激（tES）研究一直受到效果不一致的困扰。最近的研究表明，神经解剖学和神经生理学的变异性可能会改变 tES 的疗效。然而，直接证据有限。
我们之前已经复制了经颅交流电刺激（tACS）改善年轻成年人多任务处理能力的效果。在这里，我们试图评估这些刺激参数在老年成年人（60-80 岁）中是否具有类似的效果，而这一年龄段的人群在神经解剖学和神经生理学方面的变异性更大。假设这种神经解剖学和神经生理学的变异性将预测 tACS 的疗效。
我们进行了一项预先注册的研究，在多任务期间，将 tACS 施加于前额叶皮层（F3-F4 电极之间）。参与者被随机分配接受 6-Hz（θ）tACS 每日 26.67 分钟（共 80 分钟；长暴露θ组）、6-Hz tACS 每日 5.33 分钟（共 16 分钟；短暴露θ组）或 1-Hz tACS 每日 26.67 分钟（共 80 分钟；对照组）。为了考虑神经解剖学，使用磁共振成像数据形成大脑内 tACS 诱导电场（EF）的个体化模型。为了考虑神经生理学，使用脑电图数据来识别个体的θ波峰值频率。
结果表明，只有在长θ组中，性能变化与模型化的 EF 和峰值θ波频率相关。总的来说，模型化的 EF 和峰值θ波频率共同解释了 tACS 相关性能提高的 54%-65%的方差，这种提高持续了一个月。
这些结果表明了神经解剖学和神经生理学个体差异在 tACS 研究中的重要性，并有助于解释研究之间不一致的效果。
