Comparative Simulation Study of Needle Electrodes and Pad Electrodes for Human Scalp Electrical Stimulation: Analysis of Focality for tDCS Effects

Transcranial direct current stimulation(tDCS) is a noninvasive brain stimulate using low-intensity currents in the range of 0-2 mA technique. tDCS is widely used to treat brain nervous system disorders such as depression and stroke. The effectiveness of tDCS depends on various parameters that affect the electromagnetic stimulation, especially the type of electrode. This study explores how the shape of the electrode affects the focus of the electromagnetic stimulation in tDCS. For the simulation, average head model of a 20-24year old male from Electronics and Telecommunications Research Institute (ETRI) in the south korea was used. Three electrode configurations were tested: (1) two circle pad electrodes, (2) one circle pad and needle electrode, and (3) two needle electrodes. The electromagnetic simulations were performed in MATLAB 2022b based on the finite element method (FEM), assigning the same electrical conductivity to the human tissue and the electrodes. The results showed that the needle electrodes provided more focused electromagnetic stimulation compared to the conventional pad electrodes, showing a reduction in the electric field and current density. These findings highlight the important role of electrode geometry in influencing electric field and current density distribution during tDCS and suggest that needle electrodes may improve the precision of neuromodulation interventions by improving focality.