Background

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.

Objective

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.

Methods

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

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.

Conclusion

These results demonstrate the importance of individual differences in neuroanatomy and neurophysiology in tACS research and help account for inconsistent effects across studies.

中文翻译：

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神经解剖学和神经生理学的个体差异预测经颅交流电刺激的效果

背景

无创经颅电刺激 (tES) 研究一直受到不一致影响的困扰。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 的功效。然而，直接证据是有限的。

客观的

我们之前已经复制了经颅交流电刺激 (tACS) 对提高年轻人多任务处理能力的影响。在这里，我们试图评估这些刺激参数是否对老年人（60-80 岁）有类似的影响，这是一个已知在神经解剖学和神经生理学方面具有更大变异性的人群。据推测，神经解剖学和神经生理学的这种变异性将预测 tACS 疗效。

方法

我们进行了一项预先注册的研究，其中 tACS 应用在前额叶皮层上方（电极 F3-F4 之间），而参与者则从事多任务处理。参与者被随机分配接受 6-Hz (theta) tACS，每天 26.67 分钟，持续三天（总共 80 分钟；长时间暴露 Theta 组），每天 5.33 分钟的 6-Hz tACS（总共 16 分钟；短时间暴露 Theta 组） ，或 1-Hz tACS 26.67 分钟（总共 80 分钟；对照组）。为了解释神经解剖学，磁共振成像数据被用来形成大脑内 tACS 诱导电场 (EF) 的个性化模型。考虑到神经生理学，使用脑电图数据来识别个体峰值 theta 频率。

结果

结果表明，仅在 Long Theta 组中，性能变化与建模的 EF 和峰值 theta 频率相关。模型化的 EF 和峰值 theta 频率共同占 tACS 相关性能改进方差的 54%–65%，这种改进持续了一个月。

结论

这些结果证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影响。