The main cause of Parkinson's is unknown, they have no idea what causes it. There is a positive correlation between aluminum and Parkinson's but that's all it is, correlation, not causation. It may be all genetic, it may be all environmental, it may be a combination, all current research is still in the early stages.
That being said James Toney is not mentally healthy and Ali's rope-a-dope style most definitely attributed to some form of negative mental health. Letting someone punch you in the head until they get tired is never going to be good for your brain and Toney can hardly form a sentence.