The Effect of a Transcranial Channel as a Skull/Brain Interface in High-Definition Transcranial Direct Current Stimulation—A Computational Study

Abstract

A transcranial channel is an interface between the skull and brain; it consists of a biocompatible and highly conductive material that helps convey the current induced by transcranial direct current stimulation (tDCS) to the target area. However, it has been proposed only conceptually, and there has been no concrete study of its efficacy. In this work, we conducted a computational investigation of this conceptual transcranial model with high-definition tDCS, inducing focalized neuromodulation to determine whether inclusion of a transcranial channel performs effectively. To do so, we constructed an anatomically realistic head model and compartmental pyramidal neuronal models. We analyzed membrane polarization by extracellular stimulation and found that the inclusion of a transcranial channel induced polarization at the target area 11 times greater than conventional HD-tDCS without the transcranial channel. Furthermore, the stimulation effect of the transcranial channel persisted up to approximately 80%, even when the stimulus electrodes were displaced approximately 5 mm from the target area. We investigated the efficacy of the transcranial channel and found that greatly improved stimulation intensity and focality may be achieved. Thus, the use of these channels may be promising for clinical treatment.

Differences in high-definition transcranial direct current stimulation over the motor hotspot versus the premotor cortex on motor network excitability

“…In contrast, high-definition tDCS (HD-tDCS) devices provide the ability to increase stimulation focality 28 , making it potentially easier to differentially target M1 versus PMd. Although there is still likely some overlap in the stimulation due to the anatomical proximity of these regions, the ring configuration of the HD-tDCS montage helps to concentrate the peak stimulation over the desired region, and in fact, previous electrical field modeling studies have shown that the ring configuration does contain the stimulation to the central electrode 29–31 .…”

Multi-Scale Computational Models for Electrical Brain Stimulation

“…When the influence of anisotropic white matter conductivity on the stimulation effects of invasive stimulation was investigated, anisotropic models showed a strong influence on layer 5 PN and observations consistent with the empirical findings that anodal stimulation has a lower threshold than does cathodal stimulation (Seo et al, 2015 ). Further, to achieve intense and focalized neuromodulation with minimal invasiveness, a transcranial channel that was implanted in the patient’s skull was introduced (Wingeier and Pless, 2015 ), and thereafter, the channel’s effect on activation of cortical neurons was investigated using the anatomically realistic head model (Seo et al, 2017a , b ). The transcranial channel combined with TCS with direct current (transcranial direct current stimulation: tDCS) was introduced, and head models with two types of tDCS montages, a conventional tDCS using large patch-type electrodes and high-definition tDCS (HD-tDCS) using small disc-type electrodes, were constructed with and without the transcranial channel.…”

“…The transcranial channel combined with TCS with direct current (transcranial direct current stimulation: tDCS) was introduced, and head models with two types of tDCS montages, a conventional tDCS using large patch-type electrodes and high-definition tDCS (HD-tDCS) using small disc-type electrodes, were constructed with and without the transcranial channel. Seo et al ( 2017a , b ) found that the transcranial channel allowed a better targeting neuromodulation that increased both spatial focality and intensity of the neuronal excitability at the target area.…”

“…Consistent patterns of neuronal polarization according to stimulus polarities have been found in modeling results of electrical stimulation. For example, tDCS with an active electrode (anode) placed close to the precentral gyrus activated neurons in compartmental-specific manners; apical dendrites were hyperpolarized, and compartments below the soma, including basilar dendrites, were depolarized simultaneously (see Figure 3 in Seo et al, 2017b ). For magnetic stimulation, while the TMS-induced electric field is constrained on the top of the gyrus, cortical activation in the sulcus has been observed via imaging and modeling studies (Fox et al, 2004 ; Krieg et al, 2013 ; Janssen et al, 2015 ; Seo et al, 2016b ).…”

“…However, the activating function shows simple inverted signs between anodal (when the positive electrode, the anode, is located close to the target area and the reference electrode is situated far away) and cathodal stimulations (when the negative electrode, the cathode, is located close to the target area) because of the linearity of the head model with respect to electric fields. Thus, interpolation using electric fields may be quite trivial, because it ignores inherently complicated features of neurons, such as their structures, electrical properties and functions (Chan and Nicholson, 1986 ; Bikson et al, 2004 ; Radman et al, 2009 ; Seo et al, 2017b ).…”