Injection of a small amount of clumped protein triggers a cascade of events leading to a Parkinson’s-like disease in mice, according to an article published online this week in the Journal of Experimental Medicine. Progressive accumulation of clumps of the protein alpha-synuclein in the brains of patients with Parkinson’s disease coincides with the onset of motor dysfunction. However, whether these clumps are sufficient to trigger neurodegeneration, and how these clumps spread throughout the brain, remained unclear.