Apparently Parkinson disease comes with a decline in the dopamine producing parts of the brain. Or something.
A problem is that any experiments undertaken in relation to techniques or drugs related to the treatment of Parkinson’s are almost always positively efficacious. Even in the control groups.
Eventually someone postulated that just the idea that something was being done to help, was enough to stimulate dopanine production in the Parkinson’s brain. And thereby produced a good result.