Mona Lisa syndrome: solving the enigma of the Gioconda smile.

The Mona Lisa smile is presented as a possible example of facial muscle contracture that develops after Bell's palsy when the facial nerve has undergone partial wallerian degeneration and has regenerated. The accompanying synkinesis would explain many of the known facts surrounding the painting and is a classic example of Leonardo da Vinci as the compulsive anatomist who combined art and science.