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Première conférence internationale sur le bâillement
First International Conference on Yawning
Paris 24 - 25 juin 2010
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 andrew gallup
Yawning: a thermoregulatory behavior
Andrew C. Gallup (website of this author)
Department of Biological Sciences at Binghamton University, New York, USA
Gordon G. Gallup Jr
Department of Psychology, University at Albany, New York, USA
Andrew C. Gallup. Yawning and the thermoregulatory hypothesis
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 much 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.

Yawning is a widespread behavioral response expressed in all classes of vertebrates. There is however, little agreement on its biological significance. One current hypothesis states that yawning serves as a thermoregulatory mechanism that occurs in response to increases in brain and/or body temperature. The physiological consequences of yawning are concordant with those needed to effectively cool the brain, such as increases in peripheral and cerebral blood flow.
The "brain cooling hypothesis" states that yawning serves to keep the brain in thermal homeostasis, and that yawning serves to maintain optimal mental efficiency. According to this view, yawning functions as a compensatory cooling mechanism when other mechanisms fail to operate favorably. A growing body of medical and physiological evidence shows that excessive yawning is symptomatic of conditions that increase brain and/or body temperature (e.g., multiple sclerosis, epilepsy). Likewise, drugs that increase brain temperature (e.g., certain serotonin reuptake inhibitors) frequently produce excessive yawning, while drugs that produce hypothermia (e.g., opioids) inhibit yawning.
This research suggests the existence of an important connection between yawning and thermoregulation, which has been heretofore been overlooked or ignored by modern and traditional theorists. This model provides a unifying theory regarding the proximate mechanism of yawning in endotherms, offering numerous testable hypotheses.
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