Impact of Electrode Number on the Performance of High-Definition Transcranial Direct Current Stimulation (HD-tDCS).

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation for treating brain disorders by applying constant current through scalp towards the targeted cortex regions. Precisely activating or inhibiting a specific area without interfering other parts in the brain is a challenge of tDCS. Recently high-definition tDCS (HD-tDCS) with optimization technique attracts a lot of attention due to the improved focality. Unlike conventional tDCS which utilizes two large pads to deliver current to certain area, HD-tDCS employs tens of smaller electrodes. The purpose of this work is to study the effect of the electrode number on the performance of HD-tDCS. A realistic head model with four layers of tissue was constructed with different electrode montages. A systematic simulation study was conducted using targets in different regions with different functions to analyze the focusing capability, stimulation accuracy, and the intensity of constrained least square based optimized HD-tDCS. Results show that better performance in all three aspects can be achieved by increasing the electrode number.