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Yawning cools the brain down

29th November 2011

People who yawn frequently may have an underlying medical condition, according to a recent US study.

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The researchers wrote that their theory had medical implications, since yawning often preceded both epileptic seizures and migraine headaches.

Study co-author Andrew Gallup, of Princeton University, said that excessive yawning appeared to be symptomatic of conditions that increased people's body temperature, including their brain temperature.

He said that central nervous system damage and sleep deprivation could both cause excessive yawning, and that the brain was very protective of itself when it came to temperature changes.

Since ancient times, people have wondered why the majority of mammals, birds, and reptiles have so-called paranasal sinuses, four sacs of air on the front of the face.

Some people have hypothesized that the paranasal sinuses warm air before it enters the bloodstream as oxygen.

However, they seem to cool air instead, and some studies have shown that populations adapted to hot climates have larger paranasal sinuses that populations adapted to cold weather.

Co-author Gary D. Hack, of the University of Maryland, said that very little was understood about the four organs, and that some scientists believed that they had no function.

Some studies have proposed that the cooling effect comes about when cool blood passes through the sinuses, evaporating mucus.

In humans, the thin wall of one of the two pairs of paranasal sinuses may flex while people yawn, actively ventilating the sinus system and ultimately cooling the brain, which had been observed to occur in birds.

The researchers wrote that mechanisms for selectively cooling the brain were well-documented in mammals and birds, and that these structures helped animals maintain a normal brain temperature even during extreme overheating.

Birds also induce the same type of brain cooling by opening and closing their jaws, inflating a sac located behind their sinuses with air that ventilates the brain.

Previous studies have shown that certain drugs which increase brain temperature also cause excessive yawning.

By asking patients if they yawn frequently, doctors may be able to probe for pre-existing conditions of diseases that cause people to have trouble regulating body temperature, such as multiple sclerosis.

 

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