Yawning Saves Your Brain From Overheating
Posted by huehueteotl on June 25th, 2007
The next time you “catch a yawn” from someone across the room, you’re not copying their sleepiness, you’re participating in an ancient, hardwired ritual that might have evolved to help groups stay alert as a means of detecting danger. That’s the conclusion of University at Albany researchers Andrew C. Gallup and Gordon G. Gallup, Jr. in a study outlined in the May 2007 issue in Evolutionary Psychology.
The psychologists, who studied yawning in college students, concluded that people do not yawn because they need oxygen, since experiments show that raising or lowering oxygen and carbon dioxide in the blood fails to produce the reaction. Rather, yawning acts as a brain-cooling mechanism. The brain burns up to a third of the calories we consume, and as a consequence generates heat.
According to Gallup and Gallup, our brains, not unlike computers, operate more efficiently when cool, and yawning enhances the brain’s functioning by increasing blood flow and drawing in cooler air.
To research the theory that yawning evolved to cool the brain, the UAlbany psychologists had students watch videotapes of people yawning and counted the number of contagious yawns. In one experiment they found that 50 percent of the people who were instructed to breathe normally or through their mouths yawned while watching other people yawn, while those told to breathe through their nose did not yawn at all.
In another experiment they found that subjects who held a cold pack to their forehead acted similarly to those who were instructed to breathe through their nose — they, too, did not yawn, while those who held a warm pack or a room temperature pack to their forehead yawned normally.
Evidence shows that blood vessels in the nasal cavity and face send cool blood to the brain, and by breathing through the nose or by cooling the forehead, the brain is cooled, eliminating the need to yawn. Recent evidence has linked multiple sclerosis, a demyelinating disease, to thermoregulatory dysfunction. Excessive yawning is a common symptom of multiple sclerosis, and some MS patients report brief symptom relief after they yawn.
The UAlbany researchers also suggest, again contrary to popular opinion, that yawning does not promote sleep but helps mitigate the need to sleep. Since yawning occurs when brain temperature rises, sending cool blood to the brain serves to maintain optimal levels of mental efficiency. Therefore, the psychologists say, when mental processing slows and someone yawns, the tendency for other people to yawn contagiously might have evolved to promote group vigilance as a means of detecting danger.
So the next time you are telling a story and a listener yawns there is no need to be offended — yawning, a physiological mechanism designed to maintain attention, turns out to be a compliment.