The article says it was conducted on "healthy volunteers", which I assume means, folk without PD...I thought if you responded to levodopa it meant you had PD! How can this be a test?

Also, I would be curious to see what effects those healthy volunteers had, did they run faster, move more smoothly, feel profoundly more happy? That would be very interesting to me, to see what happens when you give a non-PD person levodopa.