Modeling the electric field induced in a high resolution realistic head model during transcranial current stimulation

Abstract

Much of our knowledge about the electric field distribution in transcranial current stimulation (tCS) still relies on results obtained from layered spherical head models. In this work we created a high resolution finite element model of a human head by segmentation of MRI images, and paid particular attention to the representation of the cortical sheet. This model was then used to calculate the electric field induced by two electrodes: an anode placed above the left motor cortex, and a cathode placed over the right eyebrow. The results showed that the maxima of the current density appear located on localized hotspots in the bottom of sulci and not on the cortical surface as would be expected from spherical models. This also applies to the components of the current density normal and tangential to the cortical surface. These results show that such highly detailed head models are needed to correctly predict the effects of tCS on cortical neurons.

Transcranial Current Brain Stimulation (tCS): Models and Technologies

“…Sadleir built a realistic head model incorporating ten different tissues and examined the current density in various predefined regions of interest in the brain [39]. The model presented in [40] emphasized an accurate representation of the cortical surfaces, particularly the CSF-gray matter interface, and contrary to expectation, the current density was found to be low in the gyri directly under a 25 cm electrode. Parazzini et al used a head model with 40 different tissue types and investigated the effect of electrode area on the electric field distribution [41].…”

Understanding the behavioural consequences of noninvasive brain stimulation

“…Moreover, evidence from in vivo recording [20,21] and human neuroimaging [22][23][24][25][26][27] studies suggests that tES effects are not constrained to the cortex underneath an electrode. Simulations of current flow in the brain suggest a widespread and complex distribution of induced currents [28][29][30] that can expose both cortical and subcortical regions to currents of sufficient intensity to affect neural activity. Furthermore, profound reversals in polarity can occur across sulcal and gyral elements within the vicinity of the same electrode [29,31,32], so electrode montage alone does not dictate current flow.…”

Transcranial Electrical Stimulation

“…In the pyramidal cortical neurons under the cathode, apical dendritic regions of the neuron become depolarized (red) whereas the somatic regions become hyperpolarized (blue). extracephalic electrodes, the midbrain and spinal cord (Bikson, Datta, Rahman, & Scaturro, 2010;Brunoni et al, 2012;DaSilva et al, 2012;Keeser et al, 2011;Miranda et al, 2006;Salvador, Mekonnen, Ruffini, & Miranda, 2010;Zaghi, Acar, Hultgren, Boggio, & Fregni, 2010). This farreaching activation is thought to be due to the stimulation of regions on alternate neural networks (Nitsche et al, 2005).…”