Global sensitivity of EEG source analysis to tissue conductivity uncertainties

Abstract

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.

Accuracy of dipole source reconstruction in the 3-layer BEM model against the 5-layer BEM-FMM model

“…The use of AMR should eliminate the discrepancies caused by the different number of triangles in the initial layers, so a possible explanation for the different variabilities is that Headreco meshes use a more realistic skull layer than the FreeSurfer meshes. However, a formal assessment of the effect of mesh uncertainty would require a more detailed analysis using techniques similar to those in (Vorwerk, Aydin, et al 2019; Vorwerk, Wolters, and Baumgarten 2024).…”

“…We tested three tissue conductivity sets for each subject, which we labeled (Hasgall et al 2022; Gabriel 1996), (Vorwerk, Wolters, and Baumgarten 2024; Vorwerk, Aydin, et al 2019), and (Saturnino et al 2019). Its values can be found in Table 1, for an additional reference on the conductivity of living tissues see (Knösche and Haueisen 2022).…”