生物谷报道：哈欠人人打，但可能很少有人留意到打哈欠后会感觉头脑更冷静、注意力更集中。不信？你现在就可以打个哈欠试试。
美国纽约州立大学的心理学家在最新一期《新科学家》杂志上报告说，研究显示，打哈欠可促进血液流动，“冷却”大脑，提高大脑灵敏度。这一研究结果也可以解释为什么打哈欠会“传染”。心理学家说，打哈欠“传染”是移情机制发挥作用，有助于提高群体注意力。
科学家征募了４４名大学生，让他们分别单独观看人们打哈欠的影片，并记录每名志愿者“传染性”打哈欠的次数。学生们被要求以下列４种方式之一呼吸：完全用口呼吸、完全用鼻呼吸、戴上鼻塞用口呼吸或正常呼吸。
科学家发现，观看别人打哈欠时，那些被要求正常呼吸或用口呼吸的人有一半打哈欠；而被要求用鼻呼吸的人没有一个打哈欠。科学家还发现，那些前额上放一个冷敷包的人没有因观看影片而“传染”上打哈欠，而那些前额上放热敷包的人则受到“传染”而打上了哈欠。
科学家由此认为，打哈欠能够“冷却”大脑。参与这项研究的戈登·盖洛普解释说，鼻腔中的血管可以向大脑输送温度较低的血，因此通过鼻呼吸或冷却前额，能够起到与打哈欠类似的效果，使得人们没有必要再打哈欠。而除此之外的许多人都打上了哈欠，则反过来证实了打哈欠具有“冷却”大脑的功效。他推测说，大脑在“冷却”状态时工作效率会更高，因此打哈欠也许有助于提高大脑灵敏度和增强大脑功能。（引自新华网）
原始出处：
Yawning may boost brain's alertness
02 July 2007 NewScientist.com news service
Rowan Hooper
Yawning is not something we usually aim to provoke among our readers, but have a yawn now. Does your brain feel cooler? Do you feel more attentive? According to psychologists Andrew Gallup and Gordon Gallup of the State University of New York at Albany, that is why we yawn: to boost blood flow and chill the brain.
Not only that, brain-cooling explains why you can "catch" a yawn, says Gordon Gallup. "We think contagious yawning is triggered by empathic mechanisms which function to maintain group vigilance." In other words, yawn-catching evolved to help raise the attentiveness of the whole group.
The pair recruited 44 college students to watch, individually, films of people yawning and recorded the number of contagious yawns each volunteer made. Students were told to inhale and exhale in one of four ways: strictly orally; strictly nasally; orally while wearing a nose plug; or just breathe normally.
Fifty per cent of people told to breathe normally or through their mouths yawned while watching other people yawn, while none of those told to breathe through their noses yawned. The researchers also found that subjects who held a cold pack to their forehead did not catch yawns from the film, while those who held a warm or room-temperature pack yawned normally (Evolutionary Psychology, vol 5, p 92).
Blood vessels in the nasal cavity send cool blood to the brain, so breathing through the nose or cooling the forehead cools the brain and eliminates the need to yawn, says Gordon Gallup. He argues that brains operate more efficiently when cool, and that yawning enhances brain function. "According to our hypothesis, rather than promoting sleep, yawning should antagonise sleep," he says.
"Paratroopers report yawning before they jump," says Robert Provine of the University of Maryland, Baltimore County. "Yawning signals a transition between the behavioural states of wakefulness and sleepiness, and boredom to alertness."
From issue 2610 of New Scientist magazine, 02 July 2007, page 14
