How the Number and Distance of Electrodes Change the Induced Electric Field in the Cortex during Multichannel tDCS

Multichannel transcranial direct current stimulation (tDCS) is a promising approach to target neuromodulation of neural networks by making use of variable number of electrodes and distances to facilitate/inhibit specific connectivity patterns. Optimization of the electric field (EF) spatial distribution through computational models can provide a more accurate definition of the stimulation settings that are more effective. In this study, we investigate the effect of increasing the number of cathodes around a central anode placed over the target. We demonstrate that anode-cathode distance has the largest influence in the EF and using more than 3 cathodes did not result in considerable changes in the EF magnitude and direction. This could be relevant for simultaneous tDCS-electroencephalography (EEG) applications, by saving electrode positions for EEG acquisition. Clinical Relevance— This study demonstrates that distance between electrodes is more relevant than electrode number in determining the electric field distribution, and that a highly-focused stimulation can be equally effective with fewer electrodes.