OK, I'm Not Really A Cowboy has a post on treating depression via stimulation of the Vagus Nerve. It makes some intuitive sense, as that would activate parasympathetic responses. But the time frame (1-2 years) suggests something else might be happening.
I would like to add to that the work Sidney Kennedy is doing in Canada on Deep Brain Stimulation. Goldberg down at Brown University noted the same thing anecdotally when they were using DBS for treating Parkinson's, but I don't know if they're doing anything more.