Data_Sheet_1_Global sensitivity of EEG source analysis to tissue conductivity uncertainties.PDF

IntroductionTo reliably solve the EEG inverse problem, accurate EEG forward solutions based on a detailed, individual volume conductor model of the head are essential. A crucial—but often neglected—aspect in generating a volume conductor model is the choice of the tissue conductivities, as these may vary from subject to subject. In this study, we investigate the sensitivity of EEG forward and inverse solutions to tissue conductivity uncertainties for sources distributed over the whole cortex surface.MethodsWe employ a detailed five-compartment head model distinguishing skin, skull, cerebrospinal fluid, gray matter, and white matter, where we consider uncertainties of skin, skull, gray matter, and white matter conductivities. We use the finite element method (FEM) to calculate EEG forward solutions and goal function scans (GFS) as inverse approach. To be able to generate the large number of EEG forward solutions, we employ generalized polynomial chaos (gPC) expansions.ResultsFor sources up to a depth of 4 cm, we find the strongest influence on the signal topography of EEG forward solutions for the skull conductivity and a notable effect for the skin conductivity. For even deeper sources, e.g., located deep in the longitudinal fissure, we find an increasing influence of the white matter conductivity. The conductivity variations translate to varying source localizations particularly for quasi-tangential sources on sulcal walls, whereas source localizations of quasi-radial sources on the top of gyri are less affected. We find a strong correlation between skull conductivity and the variation of source localizations and especially the depth of the reconstructed source for quasi-tangential sources. We furthermore find a clear but weaker correlation between depth of the reconstructed source and the skin conductivity.DiscussionOur results clearly show the influence of tissue conductivity uncertainties on EEG source analysis. We find a particularly strong influence of skull and skin conductivity uncertainties.

为了可靠地解决脑电图（EEG）逆问题，基于详细且个体化的头部体积导体模型的精确脑电图正向解是至关重要的。在生成体积导体模型的过程中，组织导电性的选择是一个关键但又常被忽视的方面，因为这些导电性可能因个体而异。在本研究中，我们探讨了脑电图正向和逆向解对组织导电性不确定性的敏感性，特别是在全脑皮质表面分布的源点。方法：我们采用一个详细的五室头部模型，该模型区分了皮肤、颅骨、脑脊液、灰质和白质，并考虑了皮肤、颅骨、灰质和白质导电性的不确定性。我们使用有限元方法（FEM）计算脑电图正向解和目标函数扫描（GFS）作为逆向方法。为了生成大量的脑电图正向解，我们采用了广义多项式混沌（gPC）展开。结果：对于深度达到4厘米的源点，我们发现颅骨导电性对脑电图信号拓扑结构的影响最为显著，而皮肤导电性也产生了显著影响。对于更深层的源点，例如位于纵向裂隙深处，我们发现白质导电性的影响逐渐增强。导电性的变化导致源定位的变异，尤其是在沟壁上的准切向源，而位于脑回顶部的准径向源的源定位受影响较小。我们发现颅骨导电性与准切向源的源定位变异以及重建源深度之间存在强烈的关联。此外，我们还发现重建源深度与皮肤导电性之间存在明显的但较弱的关联。讨论：我们的结果清楚地表明了组织导电性不确定性对脑电图源分析的影响。我们发现颅骨和皮肤导电性不确定性产生了特别强烈的影响。