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Here's a question people are always wondering about: why do people yawn?
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We do it every day, especially when we're in a boring meeting or we didn't get enough
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sleep. So it may not surprise you that we don't really understand all the reasons behind
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why we yawn, and it's not just humans, birds do it; jaguars do it; even fetuses in the
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womb do it.
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Oscitation, the act of yawning, happens with almost all vertebrates. The explanation you
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may be familiar with is that a great big gaping yawn is the brains way of ordering you to
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take a deep breath. Supposedly it gets rid of extra carbon dioxide and brings in more
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oxygen. The problem with that is that there is absolutely no truth that yawning really
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affects your oxygen levels.
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Instead, recent studies show that yawning is your brain's natural air conditioning system,
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bringing cooler blood to chill out your overheated, overtired grey matter. So your brain actually
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heats up as it uses some 40% of your body's metabolic energy. Just like your laptop gets
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warm up when it's been playing video games for hours.
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Body temperature also rises and falls as part of your circadian rhythm, reaching its highest
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point just before we fall asleep. Which is why a series of yawns at 1am is your body's
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way of telling you to stop going on Reddit and just go to bed. So just like your computer
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has a fan to cool things down, a yawn does the same thing to your brain, allowing you
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to continue processing information effectively.
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How's that work? Well, since you asked, yawning has two parts. First, stretching your jaws
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when you yawn increases the rate of blood flow to your skull. Second, the inhalation
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sends a gulp of air into your upper nasal and oral cavities, which have mucus membranes
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covered with tons of blood vessels that project up into the forebrain.
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This is the big part of the brain responsible for receiving and processing sensory information,
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producing and understanding language, and controlling motor functions, many of the things
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involved in actually being you.
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So the cool, refreshing air entering your sinuses changes the temperature of the blood
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that's now hustling up to the brain, making you more alert, and helping you walk and talk
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and think more effectively.
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Don't believe us? Scientist's studied the brain temperatures of mice, observing increased
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temperatures before yawning and measuring a dip in temperature afterward. And a more
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simple experiment on humans asked volunteers to hold hot or cold packets to their heads
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to see if changing the temperature of their brain cases triggered yawning.
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Turns out that the hot headed participants yawned 41% of the time, while those who chilled
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out yawned only 9% of the time.
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So next time you can't stop yawning as you're falling asleep in a sweltering classroom in
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the middle of the afternoon, remember that it's literally how your brain keeps its cool.
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