(CNN)--Next time you yawn, it might not be because you're tired.
It could be to cool off your brain!
Researchers in Arizona studied 160 volunteers and found that people yawned almost twice as much in winter, when their body temperature was higher than the air around them, than in summer.
So when your brain is working overtime, researchers theorize yawning lets cool air rush in and bring your brain back down to an optimal temperature.
Scientists also said having a toasty brain could cause sleepiness-- hence, the yawning when you're tired.
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