为什么会打哈欠？竟然不是因为困...?[E525]

Yawns Help the Brain Keep Its Cool

By Christopher Intagliata

Not many scientific studies begin like this: "Many hours of watching YouTube clips. Trying to find as many yawns[打哈欠] as possible." But for Andrew Gallup, an evolutionary psychologist[进化论心理学家] who studies yawning at the State University of New York, it was all in a day's work[1].

Gallup says yawns have traditionally been known as a sign of sleepiness, or boredom. "But recent evidence suggests that yawning may function to promote brain cooling." The idea being, when you breathe in deeply, the incoming air slightly cools the brain. And stretching the jaw[下巴;下颌] increases blood flow to the brain too--another cooling factor. Reason we do it at night? "At night time when we're about to go to sleep our brain and body temperatures are at their highest point throughout the day."

And so Gallup and his colleagues found themselves hunting for cat videos on the internet--<<cat yawning sound>>--but also clips of dogs, foxes, elephants, gorillas[猩猩], hedgehogs[刺蝟], squirrels[松鼠], rats, and walruses[海象] yawning. They timed all those yawns--then compared them to each species' average brain weight, and the number of neurons[神经元] in the cerebral cortex[大脑皮层].

Their conclusion, published in Biology Letters, was that the length of a yawn was a remarkably good predictor of an animal's brain weight, and cortical neuron[皮层/皮质神经元] number--regardless of the size of its skull[脑袋;颅骨], or jawbone[下颌骨]. [Andrew C. Gallup et al., Yawn duration predicts brain weight and cortical neuron number in mammals] "What that really represents is that yawning likely serves this very basic, and fundamental neurophysiological[神经生理学] function." In other words--it helps the brain keep its cool.

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[1]all in a day's work：If something difficult, unpleasant, or strange is all in a day's work for someone, it is a usual part of their job. （棘手、不快或奇怪的事情）为分内工作

When you're a nurse, cleaning up vomit is all in a day's work.

对护士来说，打扫呕吐污物就是分内工作。

nothing special, part of the routine 没什么特别的，司空见惯

Don't worry about it. It's all in a day's work.

别担心，这没什么特别的。

Cooking is all in a day's work.

烧饭是常有的事儿。

[2]本文选自Scientific American的60-Second Science，原文链接:http://t.cn/RVEP6eE，查看完整合集，后台回复：60s

[3]音频如有问题，点击下方“阅读原文”收听。

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