Express yourself (or someone else will)

One of the therapies used for stroke patients is called functional electrical stimulation. It is used to "exercise" the muscles of facial expression on the affected side of the face.

French neurologist, Guillaume Duchenne, most notably credited for the discovery of the hereditary muscular dystrophy - Duchenne's muscular dystrophy, used electrical stimulation on live subjects to study facial expressions. He discovered that genuine smiles from true happiness are formed by muscles of the mouth and muscles of the cheeks and eyes, forming crow's feet, hence the term "Duchenne smile".

Duchenne stimulating muscles of facial expression with electricity (top). Plate from Mécanisme de la Physionomie Humaine (1862) demonstrates various expressions from Duchenne's electrical stimulation studies (bottom).