Just kidding. C’mon folks. The smallest bit of Googling… At least he doesn’t seem to have hurt himself.
NEVER connect electrodes directly to a 9 volt battery.
Sticky (TENS) electrodes are HIGHLY not recommended.
Based on his perception of the Sally Adee article/study featured on RadioLab 9-Volt Nirvana episode, YouTuber TheCharmIsGlobal attempted to replicate the experience in an experiment he called, “TDCS EXPERIMENT WITH CALL OF DUTY: BLACK OPS III” The 43 minute video is mostly onscreen playing of Call Of Duty, but he starts the video with a discussion of tDCS, applies tDCS as shown above at around 10:40, and declares victory at 42:50.
So the verdict is in, yeah, it does work! It really does work!