Computational Study on Subdural Cortical Stimulation - The Influence of the Head Geometry, Anisotropic Conductivity, and Electrode Configuration

Abstract

Subdural cortical stimulation (SuCS) is a method used to inject electrical current through electrodes beneath the dura mater, and is known to be useful in treating brain disorders. However, precisely how SuCS must be applied to yield the most effective results has rarely been investigated. For this purpose, we developed a three-dimensional computational model that represents an anatomically realistic brain model including an upper chest. With this computational model, we investigated the influence of stimulation amplitudes, electrode configurations (single or paddle-array), and white matter conductivities (isotropy or anisotropy). Further, the effects of stimulation were compared with two other computational models, including an anatomically realistic brain-only model and the simplified extruded slab model representing the precentral gyrus area. The results of voltage stimulation suggested that there was a synergistic effect with the paddle-array due to the use of multiple electrodes; however, a single electrode was more efficient with current stimulation. The conventional model (simplified extruded slab) far overestimated the effects of stimulation with both voltage and current by comparison to our proposed realistic upper body model. However, the realistic upper body and full brain-only models demonstrated similar stimulation effects. In our investigation of the influence of anisotropic conductivity, model with a fixed ratio (1∶10) anisotropic conductivity yielded deeper penetration depths and larger extents of stimulation than others. However, isotropic and anisotropic models with fixed ratios (1∶2, 1∶5) yielded similar stimulation effects. Lastly, whether the reference electrode was located on the right or left chest had no substantial effects on stimulation.

Effect of Anatomically Realistic Full-Head Model on Activation of Cortical Neurons in Subdural Cortical Stimulation—A Computational Study

“…This result was expected based on our earlier study34, where we reported the current distribution difference in SuCS between the realistic head model and the extruded slab model. The extruded slab model was more likely to overestimate neuronal activation in SuCS than was the anatomically realistic head model.…”

“…The computation study of Truong et al 38. reports the comparable variation across subjects and describes the importance of the construction of an individualized anatomically realistic head model; however, only a few studies of invasive electrical stimulation have been performed using the anatomically realistic head model223435. It is understood that invasive stimulation may stimulate a relatively smaller focal area of the brain than noninvasive stimulation; thus, the use of a more complex head model representing the whole brain area may actually be relatively less demanding.…”

“…The anatomically realistic full head model was constructed using well-known tools: FreeSurfer5051, FMRIB FSL51, and Seg3D52 (refer to Kim et al 34. for details).…”

Validation of Computational Studies for Electrical Brain Stimulation With Phantom Head Experiments

“…The current density distribution of tDCS on the individualized brain model generated by patients' MRI data has been investigated [21], and the effects of MRI-based brain geometry on the electric field induced by TMS also have been reported [22,23]. In addition, in a recent study [24], the subdural cortical stimulation (SuCS) effect was estimated in the MRI-based full head model as the magnitude of current density or electric field, with the implicit assumption that the excitability of neurons is linearly proportional to the magnitude of the current density (or electric field). Such approaches have advantages in visualizing overall current density or electric fields in the whole brain and estimating the individualized effects of stimulation, although at an increased computational cost.…”

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

“…We used the computational head model assigned to isotropic conductivity. The effects of anisotropic conductivity in brain stimulation have been addressed widely4344454647, and Suh et al . reported that there is a significant effect on stimulus-induced EF that is dependent on anisotropic skull conductivity.…”