How much current during transcranial Direct Current Stimulation (tDCS) gets into the brain vs being shunted by the skin? Well only a fraction but enough to weakly polarize neuron for neuromodulation. Computer stimulation (FEM) help illustrate how current slips around by also through brain. Its if of course montage and head-anatomy specific but the physics don't change. Visit the lab at neuralengr.com for updates on publications and tools.