...is about the work of Braak. The hallmark of PD is a "protein clot" in the sick nerve cell called a Lewy body. These are so tied to PD that the only definitive diagnosis is an autopsy showing their presence in the Substantia Nigra.

But Braak found that they didn't start there - that in fact there was almost a migration of "something" which began in the stomach wall and followed nerves by a definite route up the vagus nerve into the brain and eventually ending up in the SN. And this migratory presence leaves a trail of Lewy bodies in its wake. Virus? Toxins? Bacteria? Rolling autoimmune response?

Well, that's about as far off topic as one can get, but it is fascinating when one considers what a role GI symptoms play and how the vagus controls so much of the body and how the brainstem is where these sensory loops begin to converge on specifc areas with exotic Latin names like lunar craters (the latter of which we know more of than the former). And whatever "it" is passes through those areas one by one, leaving its Lewy body calling card behind as it heads for the SN.