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Yawning May Help the Brain Chill Out

Yawning may be a natural way of regulatingbrain temperature, a new study suggests.

U.S. researchers examined the frequency of yawns among 80 people in the winter and another 80 people in the summer and found seasonal variations.

Yawning is known to be “contagious,” the researchers pointed out. After being showed pictures of other people yawning, nearly half of the participants yawned while outdoors in winter, compared with less than one-quarter while outdoors in summer, according to the report published online Sept. 22 in the journal Frontiers in Evolutionary Neuroscience.

The finding that people yawn less often in the summer, when outdoor temperatures often exceed body temperature, suggests that yawning could be a natural brain-cooling mechanism, said the researchers at Princeton University and the University of Arizona.

“This provides additional support for the view that the mechanisms controlling the expression of yawning are involved in thermoregulatory physiology. Despite numerous theories posited in the past few decades, very little experimental research has been done to uncover the biological function of yawning, and there is still no consensus about its purpose among the dozen or so researchers studying the topic today,” study leader Andrew Gallup, a postdoctoral research associate in Princeton’s department of ecology and evolutionary biology, said in a university news release.

“Enter the brain cooling, or thermoregulatory, 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,” he added.

Yawning may help cool the brain through the deep inhalation of cool air and by enhanced blood flow to the brain caused by the stretching of the jaw.

“According to the brain cooling hypothesis, it is the temperature of the ambient air that gives a yawn its utility. Thus 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. In other words, there should be a ‘thermal window’ or a relatively narrow range of ambient temperatures in which to expect highest rates of yawning,” Gallup explained.