https://www.parkinson.org/living-with-parkinsons/treatment/s...
https://www.parkinson.org/living-with-parkinsons/treatment/s...
DBS, like you said, is rather course tech and actually quite old technology. Doctors still don't entirely know why it works, so the adjustment is often experimental. In fact prior to specialized MRI machines that they use during surgery now, the patients would remain awake during the placement (brain surgery) of the electrodes so that the surgeons would know when the placement was "correct" based on real-time assessment of their symptoms. Now they do it under MRI, but the point being it's far from an exact science.
Can't wait to see what the future holds as they improve on it. Hard to imagine a world where his symptoms are fully managed (PD is progressive degeneration, so his symptoms, even with DBS are gradually worsening with time), but it was also hard to imagine how DBS could overnight change his life in the ways it did.
The potential of brain interface technology is truly incredible -- both for good and ill.