There's been a couple of interesting tDCS papers but as far as I understand, they're hotly debated. It's hard to replicate; the little I've done w/ the devices (and rTMS, the magnetic pulse version), these things are extremely operator dependent, if you turn a few degrees the wrong way or move a cpl mm, you screw up the effect. Ideally, they should do it on a frame mounted around the head, but the psychology people felt that would totally confound their experiments...