Researchers injected clumps of the protein alpha-synuclein into mice’s stomachs and intestines. Days later the mice had aggregates of alpha-synuclein in their intestines that had spread via the vagus nerve to the brain. Months later their brains had many alpha-synuclein aggregates in their brains that negatively affected their motor function.

This is not the first study to link the gut to Parkinson’s disease. Other studies have found that cells located in the intestine spark an immune response that protects nerve cells and neurons against damage connected with Parkinson’s disease.