Geometrical Variation’s Influence on the Effects of Stimulation May be Important in the Conventional and Multi-Array tDCS–Comparison of Electrical Fields Computed

Transcranial direct current stimulation (tDCS) is an emerging non-invasive neuromodulation method that is convenient and popular for clinical use. However, there is a practical issue when tDCS is applied to actual subjects, in which the geometrical variation in each model influences the effect of the predicted electric field (EF) distribution tDCS induces, and thus, may evoke unexpected EF distributions. In this paper, we investigated the effect of geometrical variations in the conventional two-pad tDCS and multi-array tDCS. For comparison, we constructed five spherical models of various thicknesses with cerebrospinal fluid and skull, as well as three anatomical head models. Thereafter, tDCS’ stimulation effects in the primary motor cortex (Brodmann area 4) were compared with respect to the EFs induced. We observed that geometrical variation’s effect is obvious for both forms of tDCS; but regardless of inter-subject variability, the multi-array tDCS montage may yield induced EFs of comparable or higher intensity and far greater focality. Thus, the multi-array tDCS is expected to have great potential to overcome inter-subject variability.