Assessment of electric field distribution in anisotropic cortical and subcortical regions under the influence of tDCS

Abstract

The focus of this study is to estimate the contribution of regional anisotropic conductivity on the spatial distribution of an induced electric field across gray matter (GM), white matter (WM), and subcortical regions under transcranial direct current stimulation (tDCS). The assessment was conducted using a passive high-resolution finite element head model with inhomogeneous and variable anisotropic conductivities derived from the diffusion tensor data. Electric field distribution was evaluated across different cortical as well as subcortical regions under four bicephalic electrode configurations. Results indicate that regional tissue heterogeneity and anisotropy cause the pattern of induced fields to vary in orientation and strength when compared to the isotropic scenario. Different electrode montages resulted in distinct distribution patterns with noticeable variations in field strengths. The effect of anisotropy is highly montage dependent and directional conductivity has a more profound effect in defining the strength of the induced field. The inclusion of anisotropy in the GM and subcortical regions has a significant effect on the strength and spatial distribution of the induced electric field. Under the (C3-Fp2) montage, the inclusion of GM and subcortical anisotropy increased the average percentage difference in the electric field strength of brain from 5% to 34% (WM anisotropy only). In terms of patterns distribution, the topographic errors increased from 9.9% to 40% (WM anisotropy only) across the brain.

Changing head model extent affects finite element predictions of transcranial direct current stimulation distributions

“…Registration and normalization of DTI data relative to T1 data was performed prior extracting eigenvectors and FA information. There have been claims that both skull and gray matter should be considered as anisotropic [11, 28], and it is possible that addition of gray matter and skull anisotropy would produce different RDM values than demonstrated here. However, there has been no empirical data to support skull anisotropy [15].…”

“…One important feature not considered here is the issue of segmentation accuracy. Segmentation accuracy is important since miscategorization of tissues in head model could presumably affect calculation outcomes [28]. …”

The electric field distribution in the brain during TTFields therapy and its dependence on tissue dielectric properties and anatomy: a computational study

“…These studies were based on a single subject, and incorporated isotropic values for the conductivities and permittivities that were obtained from the literature. However, white matter anisotropy has been shown to influence the electric field distribution in the brain in related techniques such as electroconvulsive therapy (Lee et al 2011) and transcranial direct current stimulation (tDCS) (Shahid et al 2013, 2014, Suh et al 2012), and is expected to affect TTFields distribution in the brain, as well. Also, isotropic conductivity values are not known accurately since a wide range of values are reported in the literature (see Methods).…”

Relationship of herpes simplex encephalitis and transcranial direct current stimulation–a case report

“…Effect of tDCS on HSE exacerbation-the electric field of tDCS may facilitate migration of activated HSV-1. Shahid [31] estimated the distribution of electric field in anisotropic cortical and subcortical regions under the influence of tDCS using an electric current of 1 mA. The assessment was conducted using a passive highresolution finite element head model with inhomogeneous and variable anisotropic conductivities that were derived from diffusion tensor data.…”