Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, United States of America.
Rancho Los Amigos National Rehabilitation Center, Downey, CA, United States of America.
J Neural Eng. 2023 Mar 24;20(2):026022. doi: 10.1088/1741-2552/acc097.
Transcranial magnetic stimulation (TMS) is a non-invasive technique widely used for neuromodulation. Animal models are essential for investigating the underlying mechanisms of TMS. However, the lack of miniaturized coils hinders the TMS studies in small animals, since most commercial coils are designed for humans and thus incapable of focal stimulation in small animals. Furthermore, it is difficult to perform electrophysiological recordings at the TMS focal point using conventional coils.We designed, fabricated, and tested a novel miniaturized TMS coil (4-by-7 mm) that consisted of a C-shaped iron powder core and insulated copper wires (30 turns). The resulting magnetic and electric fields were characterized with experimental measurements and finite element modeling. The efficacy of this coil in neuromodulation was validated with electrophysiological recordings of single-unit activities (SUAs), somatosensory evoked potentials (SSEPs), and motor evoked potentials (MEPs) in rats (= 32) following repetitive TMS (rTMS; 3 min, 10 Hz).This coil could generate a maximum magnetic field of 460 mT and an electric field of 7.2 V min the rat brain according to our simulations. With subthreshold rTMS focally delivered over the sensorimotor cortex, mean firing rates of primary somatosensory and motor cortical neurons significantly increased (154±5% and 160±9% from the baseline level, respectively); MEP and SSEP amplitude significantly increased (136±9%) and decreased (74±4%), respectively.This miniaturized C-shaped coil enabled focal TMS and concurrent electrophysiological recording/stimulation at the TMS focal point. It provided a useful tool to investigate the neural responses and underlying mechanisms of TMS in small animal models. Using this paradigm, we for the first time observed distinct modulatory effects on SUAs, SSEPs, and MEPs with the same rTMS protocol in anesthetized rats. These results suggested that multiple neurobiological mechanisms in the sensorimotor pathways were differentially modulated by rTMS.
经颅磁刺激（TMS）是一种广泛用于神经调节的非侵入性技术。动物模型对于研究 TMS 的潜在机制至关重要。然而，由于大多数商用线圈是为人类设计的，因此无法在小动物中进行聚焦刺激，因此微型化线圈的缺乏阻碍了小动物的 TMS 研究。此外，使用传统线圈很难在 TMS 焦点进行电生理记录。我们设计、制造和测试了一种新型微型 TMS 线圈（4×7 毫米），它由 C 形铁粉芯和绝缘铜线（30 匝）组成。通过实验测量和有限元建模对产生的磁场和电场进行了表征。通过对 32 只大鼠进行重复 TMS（3 分钟，10 Hz）后的单个单位活动（SUA）、体感诱发电位（SSEP）和运动诱发电位（MEP）的电生理记录，验证了该线圈在神经调节中的有效性。根据我们的模拟，该线圈在大鼠大脑中可产生最大 460 mT 的磁场和 7.2 V min 的电场。通过在感觉运动皮层上进行亚阈值 rTMS 焦点传递，初级体感和运动皮层神经元的平均放电率显著增加（分别比基线水平增加 154±5%和 160±9%）；MEP 和 SSEP 幅度显著增加（136±9%）和减少（74±4%）。这种微型 C 形线圈能够进行焦点 TMS 并在 TMS 焦点处进行同时的电生理记录/刺激。它为研究小动物模型中 TMS 的神经反应和潜在机制提供了有用的工具。使用这种范式，我们首次在麻醉大鼠中观察到相同 rTMS 方案对 SUA、SSEP 和 MEP 产生明显的调制作用。这些结果表明，感觉运动通路中的多个神经生物学机制被 rTMS 不同程度地调节。
