The effect of meninges on the electric fields in TES and TMS. Numerical modeling with adaptive mesh refinement

• Published in: Brain stimulation Vol. 15; no. 3; pp. 654 - 663
• Main Authors: Weise, Konstantin, Wartman, William A., Knösche, Thomas R., Nummenmaa, Aapo R., Makarov, Sergey N.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.05.2022; Elsevier
• Subjects: Brain stimulation; Electric field; Head modeling; Meninges; Segmentation; Transcranial electric stimulation; Transcranial magnetic stimulation; Transcranial electric stimulation; Electric field; Transcranial magnetic stimulation; Segmentation; Head modeling; Meninges; Brain stimulation
• ISSN: 1935-861X; 1876-4754; 1876-4754
• DOI: 10.1016/j.brs.2022.04.009

When modeling transcranial electrical stimulation (TES) and transcranial magnetic stimulation (TMS) in the brain, the meninges – dura, arachnoid, and pia mater – are often neglected due to high computational costs. We investigate the impact of the meningeal layers on the cortical electric field in TES and TMS while considering the headreco segmentation as the base model. We use T1/T2 MRI data from 16 subjects and apply the boundary element fast multipole method with adaptive mesh refinement, which enables us to accurately solve this problem and establish method convergence at reasonable computational cost. We compare electric fields in the presence and absence of various meninges for two brain areas (M1HAND and DLPFC) and for several distinct TES and TMS setups. Maximum electric fields in the cortex for focal TES consistently increase by approximately 30% on average when the meninges are present in the CSF volume. Their effect on the maximum field can be emulated by reducing the CSF conductivity from 1.65 S/m to approximately 0.85 S/m. In stark contrast to that, the TMS electric fields in the cortex are only weakly affected by the meningeal layers and slightly (∼6%) decrease on average when the meninges are included. Our results quantify the influence of the meninges on the cortical TES and TMS electric fields. Both focal TES and TMS results are very consistent. The focal TES results are also in a good agreement with a prior relevant study. The solver and the mesh generator for the meningeal layers (compatible with SimNIBS) are available online. •The impact of the meningeal layers on the electric field in TES and TMS is investigated.•The boundary element fast multipole method with adaptive mesh refinement is used.•TES fields in the cortex increase by 30% when the meninges are included.•TMS fields decrease by 5% on average when the meninges are included.•The solver, the mesh generator, and an example data set is made publicly available.