Henry H. Wheeler, Jr Brain Imaging Center, University of California, Berkeley, CA, United States of America.
Department of Psychology and Helen Wills Neuroscience Institute, University of California, Berkeley, CA, United States of America.
J Neural Eng. 2021 May 26;18(4). doi: 10.1088/1741-2552/abebee.
Noninvasive brain stimulation (NIBS) by quasistatic electromagnetic means is presently comprised of two methods: magnetic induction methods (transcranial magnetic perturbation or TMP) and electrical contact methods (transcranial electric perturbation or TEP). Both methods couple to neuronal systems by means of the electric fields they produce. Both methods are necessarily accompanied by a scalp electric field which is of greater magnitude than anywhere within the brain. A scalp electric field of sufficient magnitude may produce deleterious effects including peripheral nerve stimulation and heating which consequently limit the spatial and temporal characteristics of the brain electric field. Presently the electromagnetic NIBS literature has produced an accurate but non-generalized understanding of the differences between the TEP and TMP methods.The aim of this work is to contribute a generalized understanding of the differences between the two methods which may open doors to novel TEP or TMP methods and translating advances, when possible, between the two methods.This article employs a three shell spherical conductor head model to calculate general analytical results showing the relationship between the spatial scale of the brain electric fields and: (1) the scalp-to-brain mean-squared electric field ratio for the two methods and (2) TEP-to-TMP scalp mean-squared electric field ratio for similar electric fields at depth.The most general result given is an asymptotic limit to the TEP-to-TMP ratio of scalp mean-squared electric fields for similar electric fields at depth. Specific example calculations for these ratios are also given for typical TEP electrode and TMP coil configurations. While TMP has favorable mean-squared electric field ratios compared to TEP this advantage comes at an energetic cost which is briefly elucidated in this work.
目前，无创脑刺激（NIBS）通过准静态电磁手段包括两种方法：磁感应方法（经颅磁刺激或 TMP）和电接触方法（经颅电刺激或 TEP）。这两种方法都通过它们产生的电场与神经元系统耦合。这两种方法都必然伴随着头皮电场，头皮电场的幅度大于大脑内的任何地方。足够大的头皮电场可能会产生有害影响，包括外周神经刺激和加热，从而限制大脑电场的空间和时间特征。目前，电磁 NIBS 文献对 TEP 和 TMP 方法之间的差异产生了准确但非概括性的理解。本工作的目的是对这两种方法之间的差异进行概括性的理解，这可能为新型 TEP 或 TMP 方法开辟途径，并在可能的情况下在这两种方法之间进行进展的转化。本文采用三层球形导体头部模型来计算一般解析结果，这些结果显示了大脑电场的空间尺度与：（1）两种方法的头皮-大脑均方电场比，以及（2）在深度处类似电场的 TEP 与 TMP 头皮均方电场比之间的关系。给出的最一般结果是深度处类似电场的 TEP 与 TMP 头皮均方电场比的渐近极限。还针对典型的 TEP 电极和 TMP 线圈配置给出了这些比率的具体示例计算。虽然 TMP 与 TEP 相比具有有利的均方电场比，但这种优势是以能量成本为代价的，本文对此进行了简要阐述。
