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  • Here's a question people are always wondering about: why do people yawn?

  • We do it every day, especially when we're in a boring meeting or we didn't get enough

  • sleep. So it may not surprise you that we don't really understand all the reasons behind

  • why we yawn, and it's not just humans, birds do it; jaguars do it; even fetuses in the

  • womb do it.

  • Oscitation, the act of yawning, happens with almost all vertebrates. The explanation you

  • may be familiar with is that a great big gaping yawn is the brains way of ordering you to

  • take a deep breath. Supposedly it gets rid of extra carbon dioxide and brings in more

  • oxygen. The problem with that is that there is absolutely no truth that yawning really

  • affects your oxygen levels.

  • Instead, recent studies show that yawning is your brain's natural air conditioning system,

  • bringing cooler blood to chill out your overheated, overtired grey matter. So your brain actually

  • heats up as it uses some 40% of your body's metabolic energy. Just like your laptop gets

  • warm up when it's been playing video games for hours.

  • Body temperature also rises and falls as part of your circadian rhythm, reaching its highest

  • point just before we fall asleep. Which is why a series of yawns at 1am is your body's

  • way of telling you to stop going on Reddit and just go to bed. So just like your computer

  • has a fan to cool things down, a yawn does the same thing to your brain, allowing you

  • to continue processing information effectively.

  • How's that work? Well, since you asked, yawning has two parts. First, stretching your jaws

  • when you yawn increases the rate of blood flow to your skull. Second, the inhalation

  • sends a gulp of air into your upper nasal and oral cavities, which have mucus membranes

  • covered with tons of blood vessels that project up into the forebrain.

  • This is the big part of the brain responsible for receiving and processing sensory information,

  • producing and understanding language, and controlling motor functions, many of the things

  • involved in actually being you.

  • So the cool, refreshing air entering your sinuses changes the temperature of the blood

  • that's now hustling up to the brain, making you more alert, and helping you walk and talk

  • and think more effectively.

  • Don't believe us? Scientist's studied the brain temperatures of mice, observing increased

  • temperatures before yawning and measuring a dip in temperature afterward. And a more

  • simple experiment on humans asked volunteers to hold hot or cold packets to their heads

  • to see if changing the temperature of their brain cases triggered yawning.

  • Turns out that the hot headed participants yawned 41% of the time, while those who chilled

  • out yawned only 9% of the time.

  • So next time you can't stop yawning as you're falling asleep in a sweltering classroom in

  • the middle of the afternoon, remember that it's literally how your brain keeps its cool.

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Here's a question people are always wondering about: why do people yawn?

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