A thermoregulatory behavior.

The existence of yawning across vertebrate species suggests important basic functions, and the spontaneous and involuntary nature of a yawn lends support for it having adaptive significance. Recent research suggests the biological function of yawning among homeotherms is central thermoregulation. Comparative research from birds, rats and humans shows that yawning reduces brain and body temperature, is influenced by the range and direction of ambient temperature change, and is inhibited by methods of behavioral cooling. This research provides strong support for the view that yawning stimulates or facilitates cortical arousal, demonstrating that a yawn is a behavioral response to transient brain hyperthermia, acting to counter intermittent increases in brain temperature and promote thermal homeostasis. This theory is powerful because it not only integrates a great deal of seemingly diverse information about yawning, but it can also be used to generate numerous testable predictions. Applications from this research range from basic physiological understanding to the improved treatment and understanding of diseases associated with thermoregulatory dysfunction.