...on what the cause is. And if there is a complex of causes, then some yes and some no.
With that wimpy preamble- PD has elements from at least four body systems: immune (inflammation), endocrine (stress), gastrointestinal, and neural. These all interact with one another via feedback loops. That means that if you affect one then you affect all because the feedback changes.
We readily see the negative side of that when we get stressed. So it is easy to argue that we can think our self sick.
A while back we talked about a scientist named Gould who found that stress hormones can block our repair systems, so it would seem that our minds can prevent us getting well.
But can positive thoughts trigger changes that initiate healing? I don't know, but I suspect that if we could restrain ourselves enough to stay out of the way of the repair systems that would be a great start. And positive (or negative) thoughts do indeed affect our brain chemistry.
Interesting topic.