Multi-layer skull modeling and importance for tDCS simulation

Transcranial direct current stimulation (tDCS) is a popular method for non-invasive modulation of brain activity and a potential treatment for neuropsychiatric disorders. Currently the finite element head model has widely used to study tDCS. However, the typical head model ignored some extra-brain tissues, which may have a large influence on simulating the effect of tDCS. This study established a detailed head model including spongy bone to calculate the cortical electric field in tDCS. The spongy bone was extracted from the MR images and then a 6-layer head model was established. After the thickness of the skull and spongy bone was measured, the cortical electric field distributions on the detailed model and the typical model were simulated and compared. The result showed that the distribution and amplitude of electric field were different in two models, especially the distribution. The six-layer model will get a larger range of stimulus. Based on the simulation results and the real physiological structure, we conclude that it is very important to distinguish the skull into the compact bone and spongy bone for the accurate simulation of tDCS.