Gomez-Tames Jose, Tani Keisuke, Hayashi Kazuya, Tanaka Satoshi, Ueno Shoogo, Hirata Akimasa
Department of Electrical and Mechanical Engineering, Nagoya Institute of Technology, Nagoya, Japan.
Center of Biomedical Physics and Information Technology, Nagoya Institute of Technology, Nagoya, Japan.
Front Neurosci. 2021 Feb 19;15:644951. doi: 10.3389/fnins.2021.644951. eCollection 2021.
For human protection, the internal electric field is used as a dosimetric quantity for electromagnetic fields lower than 5-10 MHz. According to international standards, in this frequency range, electrostimulation is the main adverse effect against which protection is needed. One of the topics to be investigated is the quantification of the internal electric field threshold levels of perception and pain. Pain has been reported as a side effect during transcranial magnetic stimulation (TMS), especially during stimulation of the Broca's (speech) area of the brain. In this study, we designed an experiment to conduct a dosimetry analysis to quantify the internal electric field corresponding to perception and pain thresholds when targeting the Broca's and M1 areas from magnetic stimulator exposure. Dosimetry analysis was conducted using a multi-scale analysis in an individualized head model to investigate electrostimulation in an axonal model. The main finding is that the stimulation on the primary motor cortex has higher perception and pain thresholds when compared to Broca's area. Also, TMS-induced electric field applied to Broca's area exhibited dependence on the coil orientation at lower electric field threshold which was found to be related to the location and thickness of pain fibers. The derived dosimetry quantities provide a scientific rationale for the development of human protection guidelines and the estimation of possible side effects of magnetic stimulation in clinical applications.
为了保护人体，对于低于5 - 10兆赫兹的电磁场，内部电场被用作一种剂量学量。根据国际标准，在这个频率范围内，电刺激是需要防范的主要不利影响。有待研究的主题之一是感知和疼痛的内部电场阈值水平的量化。据报道，疼痛是经颅磁刺激（TMS）过程中的一种副作用，尤其是在刺激大脑的布罗卡区（语言区）时。在本研究中，我们设计了一项实验来进行剂量学分析，以量化在磁刺激器暴露下针对布罗卡区和M1区时与感知和疼痛阈值相对应的内部电场。剂量学分析是在个体化头部模型中使用多尺度分析进行的，以研究轴突模型中的电刺激。主要发现是，与布罗卡区相比，对初级运动皮层的刺激具有更高的感知和疼痛阈值。此外，在较低电场阈值下，施加于布罗卡区的TMS诱导电场表现出对线圈方向的依赖性，这被发现与痛觉纤维的位置和厚度有关。所推导的剂量学量为制定人体保护指南以及估计磁刺激在临床应用中可能产生的副作用提供了科学依据。
