“Other people tried to put tDCS on a cadaver and said that there wasn’t enough electricity that was penetrating the skull to make any difference in terms of action potentials. But the next meta-analysis found some effectiveness for depression and anxiety. The study[1], published in 2017, was one of the best out there.” 1. https://www.sciencedirect.com/science/article/abs/pii/S13882...

Article also mentions living bone is conductive.