Well, the Parkinson's thing isn't all that complicated - simple wire w/ ~ 1.5mm electrode sending out a 130Hz square wave at ~ 3 volts. It's been FDA approved

Well, the Parkinson's thing isn't all that complicated - simple wire w/ ~ 1.5mm electrode sending out a 130Hz square wave at ~ 3 volts. It's been FDA approved for over a decade now, and ~100k implants have been done worldwide. The interesting part is that no one knows why it works as well as it has. tDCS, and TMS, on the other hand, have barely measurable effects or widely variable effects, and no one has really figured out how to make them practical. Useful for all sorts of psych papers and hypothesis generation, though.