The two-century journey of Parkinson disease research.

Since the first formal description of Parkinson disease (PD) two centuries ago, our understanding of this common neurodegenerative disorder has expanded at all levels of description, from the delineation of its clinical phenotype to the identification of its neuropathological features, neurochemical processes and genetic factors. Along the way, findings have led to novel hypotheses about how the disease develops and progresses, challenging our understanding of how neurodegenerative disorders wreak havoc on human health. In this Timeline article, I recount the fascinating 200-year journey of PD research.