“Today, we accept that proteins can behave like infectious agents (e.g., viruses) and can spread widely throughout the brain and nervous system. The term prion-like has emerged and reflects the idea that, in Parkinson’s disease, proteins can spread from brain region to brain region, but this does not mean that Parkinson’s is an infection. How do they spread? We think that the secret is in how the protein folds. Certain shapes impart to the protein the superpower to move from brain cell to brain cell.”