Everyone does it, but just why people yawn has remained a mystery. Now, a new study suggests that yawning might help cool an overheated brain.
Austrian researchers found that the amount of yawning folks do varies with air temperature, with the practice becoming not so common as outside temperatures get either very hot or very cold.
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In the study, a team led by Jorg Massen of the University of Vienna tracked yawning among people who were walking outside in Vienna, Austria, during summer and winter. The researchers then compared those results to those of an identical experiment conducted in Arizona.
Participants in the studies were all shown pictures of other people yawning in order to trigger what is known as "contagious yawning," and then reported on their own yawning behavior.
People in Vienna yawned more in summer than in winter, while the reverse was true among those in Arizona -- they yawned more in winter than in summer. The researchers also found that contagious yawning was most likely to occur when the air temperature was around 68 degrees Fahrenheit.
Yawning occurred much less often when temperatures were higher-- around 98.6 degrees during the summer in Arizona -- or around the freezing point during winter in Vienna, according to the study recently published online in the journal Physiology & Behavior.
As the researchers explained, yawning to "cool" the brain would not work when air temperatures outside are as hot or hotter than the body itself. And brain cooling may not even be necessary in cold weather, Massen's team said in a university news release.
While it's widely believed that yawning helps increase the body's oxygen supply, no studies have found a link between yawning and blood oxygen levels, the researchers said. They believe that the new study adds to growing evidence that both spontaneous and contagious yawning helps cool the brain.
Cooling of the brain boosts its performance, so contagious yawning may be an evolutionary trait meant to improve overall alertness in groups of people, the study authors also suggested.
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