ber nand rivena. he's a researcher with the michael j. fox foundation. thank you for joining us. >> thank you. >> he's doing well. he had a lot to say, obviously. he pointed out, there are so many unknowns. we don't know what causes this. the treatment hasn't changed a lot. at one point he says just diagnosing him, he wasn't sure he has parkinson's disease. is that why it's difficult to make progress. >> there are many things that contribute to parkinson's disease. people with early on set parkinson's disease, it's difficult to make a diagnosis. there are several other diseases that are suspected diseases you out first. >> the distinguishing features to parkinson's disease -- the one that is the most distinguishing is that the patients respond to the medications. in the early stages. and where many of the diseases are not responsive. so this ability to respond is usually the cut point that makes you feel certain that someone has parkinson's. >> and he says he clearly responds to it. he clearly has benefit from taking the dopamine, which is deficient in t