Wake up, we were born to yawn (it stops our brains overheating)

THE glazed eyes and the futile attempt to suppress a yawn as someone rambles on has long been seen as a response to boredom or as a sign the body is in need of a rest.

But now scientists have thrown another factor into the mix by revealing yesterday that yawning can be a way of regulating brain temperature and preventing overheating.

The research, led by Andrew Gallup from Princeton University, is the first involving humans showing yawning frequency varies with the seasons and that people are less likely to yawn when the heat outdoors is greater than body temperature.

Researchers found half the participants yawned in winter while only a quarter yawned in summer when ambient temperatures equalled or exceeded body temperature.

They concluded warmer temperatures provide no relief for overheated brains, which, according to the thermoregulatory theory of yawning, stay cool via a heat exchange with the air drawn in during a yawn.

Dr Gallup, of the university’s department of ecology and evolutionary biology, and co-author Omar Eldakar, from the University of Arizona, said this seasonal disparity indicates yawning could serve as a method for regulating brain temperature.

The findings, which appear this month in the journal Frontiers in Evolutionary Neuroscience, documented the yawning frequency of 160 people in the winter and summer in Tucson, Arizona, with 80 people for each season.

Dr Gallup said very little experimental research had been conducted to uncover the biological function of yawning and there was still no consensus.

“Enter the brain cooling hypothesis, which proposes that yawning is triggered by increases in brain temperature, and that the physiological consequences of a yawn act to promote brain cooling.”

The cooling effect of yawning is thought to result from enhanced blood flow to the brain caused by stretching the jaw, as well as countercurrent heat exchange with the air that accompanies the deep inhalation.

Dr Gallup said: “According to the brain cooling theory, it is the temperature of the ambient air that gives a yawn its use. Yawning should be counterproductive – and therefore suppressed – in ambient temperatures at or exceeding body temperature because taking a deep inhalation of air would not promote cooling.”

Dr Gallup said the research could lead to a better understanding of diseases and conditions such as multiple sclerosis or epilepsy which are accompanied by frequent yawning and thermoregulatory dysfunction.

Professor Colin Espie, director of the University of Glasgow Sleep Centre, who conducted The Great British Sleep Survey, the only UK-wide survey on sleeping habits, said: “The findings are interesting but probably need muliti-disciplinary research to show their applications.

“The causes of yawning are important because they provide important feedback about the body’s biological state. I suspect a lot is down to basic 24-hour rhythms and survival instincts. Falling asleep involuntarily and losing attention could mean you die.”

Liz Wyse, etiquette advisor at Debrett’s, said: “Whatever the reasons, people should try wherever possible to refrain from yawning and, if unavoidable, should cover the mouth and utter an apology.”