Department of Electrical Engineering and Automation, Aalto University, Espoo, 02150, Finland.
Faculty of Rehabilitation, School of Health Sciences, Fujita Health University, Toyoake, 470-1192, Japan.
Sci Rep. 2019 Jan 24;9(1):626. doi: 10.1038/s41598-018-37226-x.
The effects of transcranial direct current stimulation (tDCS) on motor cortical excitability are highly variable between individuals. Inter-individual differences in the electric fields generated in the brain by tDCS might play a role in the variability. Here, we explored whether these fields are related to excitability changes following anodal tDCS of the primary motor cortex (M1). Motor evoked potentials (MEPs) were measured in 28 healthy subjects before and after 20 min sham or 1 mA anodal tDCS of right M1 in a double-blind crossover design. The electric fields were individually modelled based on magnetic resonance images. Statistical analysis indicated that the variability in the MEPs could be partly explained by the electric fields, subjects with the weakest and strongest fields tending to produce opposite changes in excitability. To explain the findings, we hypothesized that the likely locus of action was in the hand area of M1, and the effective electric field component was that in the direction normal to the cortical surface. Our results demonstrate that a large part of inter-individual variability in tDCS may be due to differences in the electric fields. If this is the case, electric field dosimetry could be useful for controlling the neuroplastic effects of tDCS.
经颅直流电刺激 (tDCS) 对运动皮质兴奋性的影响在个体之间差异很大。tDCS 在大脑中产生的电场的个体差异可能在这种变异性中起作用。在这里，我们探讨了这些电场是否与初级运动皮质 (M1) 阳极 tDCS 后的兴奋性变化有关。在双盲交叉设计中，28 名健康受试者在右 M1 接受 20 分钟假刺激或 1 mA 阳极 tDCS 之前和之后测量运动诱发电位 (MEP)。根据磁共振图像对电场进行个体建模。统计分析表明，MEP 的可变性可以部分解释为电场，电场最弱和最强的受试者倾向于产生相反的兴奋性变化。为了解释这些发现，我们假设作用的可能部位在手区的 M1，有效的电场分量是垂直于皮质表面的方向。我们的结果表明，tDCS 中很大一部分个体间变异性可能是由于电场的差异造成的。如果是这样，电场剂量测定可能有助于控制 tDCS 的神经可塑性效应。
