Theoretical investigation of transcranial alternating current stimulation using realistic head model

Transcranial alternating current stimulation (tACs) is an important new technique that allows to modulate non-invasively high-order cortical processes. The underlying mechanisms of activation of this brain stimulation technique are still poorly understood. Herein, we use a finite difference time domain (FDTD) technique to investigate the penetration and focality of tACs in comparison to a time invariant (DC) stimulation. We show that stimulation using 10 Hz generates cerebral fields that are larger (× 2.5) and more focused than DC stimulation and that faster oscillating stimuli of 100 Hz and 1000 Hz, generate smaller and less focused cerebral fields than 10 Hz. The outcomes of this study may help tACs users to design better protocols and interpret experimental results.