A computational study on effect of a transcranial channel as a skull/brain interface in the conventional rectangular patch-type transcranial direct current stimulation.

A conceptual model of a transcranial channel was recently proposed for conveying external currents of the skull to the brain; the effects of the transcranial channel combined with high-definition transcranial direct current stimulation (HD-tDCS) was investigated, resulting in discovery of increased stimulus intensity and focality. In this work, rather than HD-tDCS using smaller disc-type electrodes, we proposed the use of the transcranial channel with conventional tDCS using larger patch electrodes. We used multi-scale computational models that couple an anatomically realistic head model with multi-compartmental models of cortical neurons. We then predicted the excitability in the hand knob (target area) based on stimulus-induced electric fields and steady-state membrane polarizations. Conventional tDCS without the transcranial channel resulted in diffuse distributions of electric fields that covered the frontal cortex, while the spatial focality and intensity of the excitability increased significantly at the target area in the presence of the transcranial channel. Thus, it is expected that conventional tDCS with the transcranial channel allows a better targeting neuromodulation with higher intensity and may be promising for applying prolonged and stabilized tDCS.