Yawning in the history of psychiatry.

Yawning is a fascinating physiological behaviour that has been poorly addressed except in old medical books. Whereas the purpose of this behaviour is still not clearly identified, the ancient authors made it a clinical symptom, especially a psychological one. After presenting some current notions about yawning, we review publications on yawning written by physicians, from antiquity to the twentieth century, and, in particular, those dealing with psychological and psychiatric aspects.