-when I told him that my neurologist didn't think stress had a role in causing PD,"But, but, stress affects EVERYTHING!!"

And it does. Among other things it blocks neurogenesis and our ability to repair damage as researcher Elizabeth Gould has shown. We are built to handle acute stress and do it very well. But chronic stress is another matter and is terribly destructive.

Analogies are handy for getting our minds around this way of thinking about PD. Imagine you have a big basket on the floor in front of you and overhead is a big chute which drops a colored ping pong ball at random times and of random color every few seconds. Like an old "I Love Lucy" skit, your job is to remove the balls as they come in and sort them by color. Say red, white, or blue. So long as a certain speed is not exceeded there is no problem but above that the basket begins to fill. At some point a ball drops and rolls off the basket pile and onto the floor. Say it was a blue ball and that it hitting the floor translates into that first symptom of PD.

Now one could argue that blue balls cause PD but even if you eliminated the blue ones the outcome would not change. And the mix of colors is not relevant either. It is the rate of balls matched against your ability to remove them from the basket that is the real process. But the research money goes to trying to figure out which color of ball is the culprit.