A yawn could be more than a sign of sleepiness or a show of boredom. A new study suggests it could be a way for your brain to cool off. According to this brain-cooling theory, yawning pays off because it helps control the temperature of your brain so you think more clearly.
Researchers also noticed seasonal variations in the frequency of yawning. People appear to yawn more frequently in the winter after spending long periods of time outside in colder weather than they do in the summer heat.
"People are less likely to yawn when the surrounding air temperatures exceeds body temperature because taking a deep inhalation of air warmer than your own body would not result in cooling," says Andrew Gallup, a postdoctoral research associate in the department of ecology and evolutionary biology at Princeton University in Princeton, N.J.
The study, which was published in the journal Frontiers in Evolutionary Neuroscience, took place in Tucson, Ariz., a climate where the thermometer routinely exceeds human body temperature of 98.6 F. Researchers compared the rates of contagious yawning in 80 people who were outdoors in "winter conditions," in Tucson, meaning milder temperatures and slightly higher humidity, to 80 people in "early summer," which has hotter weather and relatively low humidity.
Researchers asked people walking on the street to complete a survey about contagious yawning. The questionnaire included 20 photos of people yawning, and contained questions about how long participants had been outside prior to the survey, how much sleep they had the night before, and how often they yawned during the experiment.
People yawn for two main reasons: They do it spontaneously because of fatigue, stress, changes in mental or physical activity, and following a circadian rhythm in the body's internal clock, says Gallup, the study's lead author. Yawning can also be socially contagious. Seeing, hearing, reading, or thinking about yawning can cause you to do the same. (And yawning during take-off and landing is a helpful trick to "pop" your ears when flying causes air pressure changes.)
Scientists found that during the winter, nearly half of the study participants reported yawning during the experiment compared to about a quarter of them in the summer. Yawning also seemed to be linked to the amount of time spent outdoors exposed to those climate conditions.
Gallup explains that yawning may act like a car radiator by removing blood from the brain that's too hot while introducing cooler blood from the lungs as well as the arms and legs. Much like an overheated engine, an overheated brain doesn't function well.
"Yawning functions to promote attention and mental efficiency by reinstating optimal brain temperature," Gallup points out. "So it should be considered a compliment rather than an insult."
If you yawned while reading this article, it could mean that you're simply sharpening your brain power to be more alert.
Readers, have you ever been caught yawning at a poorly timed moment?
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