Effect of skin conductivity on the electric field induced by transcranial stimulation techniques in different head models

Abstract

This study aims at quantifying the effect that using different skin conductivity values has on the estimation of the electric (E)-field distribution induced by transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) in the brain of two anatomical models. The induced E-field was calculated with numerical simulations inside MIDA and Duke models, assigning to the skin a conductivity value estimated from a multi-layered skin model and three values taken from literature. The effect of skin conductivity variations on the local E-field induced by tDCS in the brain was up to 70%. In TMS, minor local differences, in the order of 20%, were obtained in regions of interest for the onset of possible side effects. Results suggested that an accurate model of the skin is necessary in all numerical studies that aim at precisely estimating the E-field induced during TMS and tDCS applications. This also highlights the importance of further experimental studies on human skin characterization, especially at low frequencies.

Electric Field Characteristics of Rotating Permanent Magnet Stimulation

“…In addition, cortical folding in realistic head models can increase the maximum E-field strength compared to spherical head models [ 32 , 41 ]. It has been shown, for example, that skin conductivities’ variation can result in minor changes in E-field strength induced by TMS [ 42 ]. Future work could consider integrating realistic head models to better represent accurate head anatomy and the variations in E-field strengths across individuals.…”

How does the electric field induced by tDCS influence motor-related connectivity? Model-guided perspectives

“…The models generated by the headreco pipeline are not as detailed as other models available in literature, such as the MIDA model, which includes over 50 different tissues in a full headneck model (Iacono et al 2015). Also, models obtained by headreco do not discriminate stratification of extracerebral tissues, which impact the dielectric properties assigned to the skin and consequently the EF distribution predicted in the brain (Colella et al 2021). On the other hand, individual specific anatomical characteristics influence the current flow and thus the EF induced by tDCS, which reflects in variable outcomes from subject to subject (Hunold et al 2023).…”

“…Considering this, we decided to address inter-subject variability with realistic and personalised head models generated directly by each individual MRIs, instead of using already available and detailed literature models, such as MIDA (Iacono et al 2015). However, considering the impact of tissue stratification on the EF characteristics, future studies in this context should include more detailed models with tissue stratification towards more accurate predictions (Colella et al 2021).…”

Astrocyte Responses Influence Local Effects of Whole‐Brain Magnetic Stimulation in Parkinsonian Rats

“…The experiments performed here and in previous papers 13,14 were computationally reproduced in the Sim4Life environment (Zurich MedTech AG, Zurich) by considering the model of the 70 mm figure-of-eight stimulating coil and the male Wistar rat model taken from the ViZOO population (ie, the big rat). 31 The coil model consisted of two connected co-planar windings made of a wire with a dimensionless cross-section, 34,35 whereas the rat brain model was ad hoc modified, replacing it with the opensource Waxholm space atlas (RRD: SCR_017124), 32,33 a highly detailed three dimensional (3D) digital brain atlas. This allowed us to integrate an accurate model of the entire rat body, with a separate representation of up to 220 specific brain areas, including the targets of this study, such as the hippocampus, the striatum, and the cerebellum, and their subregions, as in Figure 1A where the full model, with the coil placed over the bregma of the 3D virtual rat, is shown.…”