WHAT Happens When We Yawn?

Yawning may no longer be a wide open question.

Yawning does not occur because you are tired, bored or even need oxygen. Instead yawning helps to regulate the brain's temperature by cooling it.

That is the theory proposed by Gary Hack, DDS of the University of Maryland School of Dentistry and Andrew Gallup, PhD of Princeton University.

"The brain is exquisitely sensitive to temperature changes and therefore must be protected from overheating," the authors write in the journal Medical Hypotheses. "Brains, like computers, operate best when they are cool."

How does yawning cool the brain? Hack and Gallup think the walls of the human maxillary sinus (pictured in green in the photo above) flex during yawning like a bellows, which in turn facilitates brain cooling.

The theory also helps explain the function of the human sinuses, which is still debated among scientists. In fact, Hack says everything concerning the human sinuses is debated. "Very little is understood about them, and little is agreed upon even by those who investigate them. Some scientists believe that they have no function at all," he said.

Hack and Gallup have a new idea, never before proposed: The human sinuses play a role in brain cooling that is driven by yawning.

Beyond the physiological curiosity, the brain cooling theory of yawning also has practical medical implications. Bouts of excessive yawning often precede the onset of seizures in epileptic patients and predict the onset of pain in people with migraine headaches, explains Gallup.

Hack and Gallup predict that excessive yawning might be able to be used as a diagnostic tool in identifying dysfunction of temperature regulation. "Excessive yawning appears to be symptomatic of conditions that increase brain and/or core temperature, such as central nervous system damage and sleep deprivation, says Gallup.

--From the Editors at Netscape

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