Duchenne Smile

A Duchenne smile is a genuine expression of positive emotion that involves both the zygomatic major muscle, which raises the corners of the mouth, and the orbicularis oculi muscle around the eyes, which produces the crinkling sometimes called crow's feet. It is named for the French neurologist Guillaume Duchenne, who studied the physiology of facial expression in the nineteenth century. A smile that uses only the mouth muscles, without the involuntary eye muscle, is generally regarded by researchers as a deliberate or social smile rather than a spontaneous expression of felt enjoyment.