Yeah... reading it in further detail, he applies current across his head between the mastoid processes. I thought it was local stimulation between two surface electrodes under the ear. A quick look at the literature shows that the targeted structures are too deep for an approach like that, so they have to go across the head.

Style points for bravery, I guess, but I certainly wouldn't want to pump over a milliamp of direct current right underneath the squishy mass of goo that contains my conscious self. Especially not with an uncontrolled source like a battery - any sort of stimulator really ought to be current limited.

A milliamp is an awful lot, IEC 60601 specifies a 0.1 mA patient leakage current and I'm pretty sure they weren't expecting even that small leakage current to be applied to the head.

It's still cool, but yeah, nobody try this at home.