 The possibility that movement disorders, including Tourette syndrome, might have an organic origin was raised when an encephalitis epidemic from 1918–1926 led to a subsequent epidemic of tic disorders.Research in 1972 advanced the argument that Tourette's is a neurological, rather than psychological, disorder; since the 1990s, a more neutral view of Tourette's has emerged, in which biological vulnerability and adverse environmental events are seen to interact.Findings since 1999 have advanced TS science in the areas of genetics, neuroimaging, neurophysiology, and neuropathology.