Investigation of the electric field components of tDCS via anisotropically conductive gyri-specific finite element head models.

Transcranial Direct Current Stimulation (tDCS) is considered as one of the promising techniques for noninvasive brain stimulation and brain disease therapy. In this study, we have investigated the effect of skull and white matter (WM) anisotropy on the induced electric field (EF) by tDCS in two different montages; one using a pair of clinically used rectangular pad electrodes and the other 4(cathodes)+1(anode) ring electrodes. Using a gyri-specific finite element (FE) head model, we simulated tDCS and investigated the radial and tangential components of the induced EF in terms of their distribution over the cortical surface besides the distribution of the transverse and longitudinal components within WM. The results show that the tangential component of the EF on the cortical surface seems to be the main cause of the cortical stimulation of tDCS. Also WM anisotropy seems to increase the dispersion of the transverse component of the EF that affects the dispersion of the EF magnitude within the WM region.