Physiological observations validate finite element models for estimating subject-specific electric field distributions induced by transcranial magnetic stimulation of the human motor cortex
Physiological observations validate finite element models for estimating subject-specific electric field distributions induced by transcranial magnetic stimulation of the human motor cortex
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DOI：
10.1016/j.neuroimage.2013.04.067
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发表时间：
2013-11-01
期刊：
影响因子：
5.7
通讯作者：
Tyler, William J.
中科院分区：
文献类型：
--
作者：
Opitz, Alexander;Legon, Wynn;Tyler, William J.
最近的证据表明，特定主题的回旋折叠模式和白色物质的各向异性独特形状的TMS产生的电场。目前用于预测受TMS影响的大脑区域的方法涉及将TMS线圈位置或重心投影到从结构和功能成像数据导出的真实头部模型上。类似地，球形模型已经被用于估计由从特定线圈位置和定位递送的TMS脉冲生成的电场分布。在本文中，我们检查使用有限元法（FEM）和上述基于投影的方法估计的电场计算之间的差异。然后，我们更具体地研究了一种方法，用于估计皮质兴奋量的基础上个性化有限元模拟电场。我们通过在MR导航运动标测实验中进行神经生理学记录来评估这种方法。我们使用两种不同的线圈方向（与中线成45度和90度）在25个不同位置（5 x 5网格，1 cm间距）记录了对单脉冲TMS的运动诱发电位（MEP），这些位置以左侧运动皮层中右侧第一背侧骨间（FDI）肌肉的热点为中心。我们观察到，受试者内部和受试者之间的运动兴奋性地图随着TMS线圈位置和方向的变化而变化。对于测试的每个线圈位置和方向，使用个体化FEM模型计算TMS诱导电场的模拟，并与我们的运动标测实验期间获得的MEP振幅进行比较。我们发现电场强度的FEM模拟（考虑了受试者特定的脑回几何形状和组织电导率各向异性）与生理学观察到的MEP幅度显著相关（r（最大值）= 0.91，p = 1.8 x 10（-5）r（平均值）= 0.81，p = 0.01）。这些观察结果验证了个体主义FEM模型的实施，以解释脑回折叠模式和组织电导率各向异性的变化，这将有助于提高TMS在人类大脑回路的映射或调制中的靶向准确性。(C)2013作者爱思唯尔公司出版All rights reserved.
Recent evidence indicates subject-specific gyral folding patterns and white matter anisotropy uniquely shape electric fields generated by TMS. Current methods for predicting the brain regions influenced by TMS involve projecting the TMS coil position or center of gravity onto realistic head models derived from structural and functional imaging data. Similarly, spherical models have been used to estimate electric field distributions generated by TMS pulses delivered from a particular coil location and position. In the present paper we inspect differences between electric field computations estimated using the finite element method (FEM) and projection-based approaches described above. We then more specifically examined an approach for estimating cortical excitation volumes based on individualistic FEM simulations of electric fields. We evaluated this approach by performing neurophysiological recordings during MR-navigated motormapping experiments. We recorded motor evoked potentials (MEPs) in response to single pulse TMS using two different coil orientations (45 degrees and 90 degrees to midline) at 25 different locations (5 x 5 grid, 1 cm spacing) centered on the hotspot of the right first dorsal interosseous (FDI) muscle in left motor cortex. We observed that motor excitability maps varied within and between subjects as a function of TMS coil position and orientation. For each coil position and orientation tested, simulations of the TMS-induced electric field were computed using individualistic FEM models and compared to MEP amplitudes obtained during our motormapping experiments. We found FEM simulations of electric field strength, which take into account subject-specific gyral geometry and tissue conductivity anisotropy, significantly correlated with physiologically observed MEP amplitudes (r(max) = 0.91, p = 1.8 x 10(-5) r(mean) = 0.81, p = 0.01). These observations validate the implementation of individualistic FEM models to account for variations in gyral folding patterns and tissue conductivity anisotropy, which should help improve the targeting accuracy of TMS in the mapping or modulation of human brain circuits. (C) 2013 The Authors. Published by Elsevier Inc. All rights reserved.