High-resolution head model of transcranial direct current stimulation: A labeling analysis

The ability of transcranial direct current stimulation (tDCS) to produce lasting polarity-specific modulatory effects continues to drive use both in research and clinical domains. Computational models of tDCS over the years have provided valuable insight on the current flow pattern and magnitude of electric field induced in the cortex. However, induced cortical values are usually not systematically quantified for different brain subcomponents that allow further investigation into the relevant contribution of these distinct regions. This information is of significant interest given different subcomponents of the brain contribute to different functions that ultimately underlie net outcomes. Thus given a particular stimulation response and the current flow pattern, one can potentially infer results in relation to current flow in different compartments (regions affected/spared, magnitude, etc.) The aim of this study is to determine tDCS induced electric field/current density using a high resolution head model incorporating a brain parcellated into 17 notable gyri and 10 sub-cortical regions. We consider both conventional tDCS and High Definition (HD)-tDCS electrode montages. The induced electrical field in each parcellated brain region is computed and compared across the two montages.Findings indicate that maximum electrical field is induced in the precentral gyrus for both the montages considered. As expected, the current flow pattern using the HD-tDCS montage considered is more restricted- both spatially and depth-wise. The conventional tDCS montage results in deeper current flow with sub-cortical structures subject to as much as 47-95% the current flow in the upper cortical regions. For the HD montage, electric field in the subcortical structures drop to 12-32% of the values induced in the upper regions. Incorporation of labeled human head models may guide rational electrode design and optimization of tDCS by providing more detailed and systematic information.