经颅电、磁扰动电场的比较
Comparing the Electric Fields of Transcranial Electric and Magnetic Perturbation
摘要：
通过准静态电磁手段的无创脑刺激（NIBS）目前包括两种方法：磁感应方法（经颅磁扰动或TMP）和电接触方法（经颅电扰动或TEP）。这两种方法都是通过它们产生的电场与神经系统耦合。这两种方法都必须伴随着头皮电场，其幅度大于大脑内的任何地方。足够大小的头皮电场可能产生有害影响，包括外周神经刺激和加热，这因此限制了大脑电场的空间和时间特性。目前，电磁NIBS文献已经对TEP和TMP方法之间的差异产生了准确但非普遍的理解。这项工作的目的是促进两种方法之间的差异，这可能打开大门，新的TEP或TMP方法和翻译的进步，在可能的情况下，两种方法之间的一般性理解。本文采用三壳球形导体头部模型计算一般分析结果，显示脑电场的空间尺度与以下因素之间的关系：（1）两种方法的头皮-脑均方电场比和（2）深度处类似电场的TEP-TMP头皮均方电场比。给出的最一般的结果是在深度处对于类似的电场，头皮均方电场的TEP-TMP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，这在本工作中进行了简要阐述。
英文摘要：
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.
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