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It's easy to be offended when a colleague yawns while you're talking. But that yawn may not mean what you think.
人們很容易會被這樣一種行為惹惱：當你說話的時候，你的同事卻在打著哈欠。但對于這個哈欠，也可能是你想得太多了。
A growing number of researchers believe the purpose of this little-understood behavior is to cool the brain, says a research review published earlier this year in Frontiers in Neuroscience.
今年早些時候發表在《神經科學前沿》(Frontiers in Neuroscience)上的一項研究綜述稱，越來越多的研究人員認為，打哈欠這種人們對其還知之甚少的行為，其目的在于為大腦降溫。
Changes in climate affect how often people yawn. Researchers in an earlier study conducted outdoor interviews with two groups of people in Tucson, Ariz., one in early summer and one in the winter. People were asked to look at pictures of people yawning and talk about their own yawning behavior.
氣候的變化會影響到人們打哈欠的頻率。研究人員在之前的一次研究中對亞利桑那州圖森市(Tucson)的兩組人進行了戶外采訪，一次是在初夏，另一次是在冬天。研究人員讓被訪者看了一些人們打哈欠的照片，并談了談他們自己的打哈欠行為。
People were nearly twice as likely to yawn when they were surveyed during the winter, when they could inhale cool air to reduce the temperature of the brain, says the study, published in 2011 in Frontiers in Evolutionary Neuroscience. Participants yawned less when surveyed in the early summer, when temperatures outdoors were about the same as the human body.
該項研究的論文2011年發表在《進化神經科學前沿》(Frontiers in Evolutionary Neuroscience)上，文章稱，這些人在冬天接受調查時打哈欠的可能性是初夏時的將近兩倍，在冬季，他們打哈欠能吸入冷空氣來給大腦降溫。而在夏初接受調查的參與者哈欠較少，因為那個時節的室外氣溫跟人的體溫幾乎是一樣的。
Other studies show yawning increases after people experience heat stress or have a heat pack placed on their foreheads.
其他一些研究則表明，在人們中暑或在前額貼上發熱貼以后，哈欠就會增多。
Yawning also may build empathy within groups. Yawns are seen as contagious, but 'catching' a yawn depends on a person's ability to feel empathy and closeness with the yawner, says a 2013 research review in the International Journal of Applied Basic Medical Research.
2013年發表在《應用基礎醫學研究國際期刊》(International Journal of Applied Basic Medical Research)上的一項研究綜述稱，哈欠可能還會在人群中形成共鳴。哈欠被認為是具有傳染性的，但是否能“接過”一個哈欠取決于個人感同身受的能力以及與打哈欠者的親密程度。
People observed in workplaces or restaurants yawned more often in response to others' yawns when they were kin or close friends with the yawner, the study says. People are less likely to engage in contagious yawns when they have emotional or social disorders that prevent them from feeling empathy, the study says.
該研究稱，據觀察，在工作場所或餐館里若有人打了哈欠，他們的親朋好友會更多地也打起哈欠。但那些因患有情緒或社交障礙而無法設身處地理解他人的人則不太可能會被別人的哈欠所感染。
What yawns don't accomplish, researchers say, is to re-energize the brain.
研究人員還稱，打哈欠無法讓大腦重新活躍起來。
For centuries, yawning was thought to remove 'bad air' from the lungs and increase oxygen circulation in the brain. Recent studies have discredited this old belief.
幾個世紀以來，人們都認為打哈欠是為了清除肺里的“廢氣”、增加大腦中的氧循環。新近的這些研究則對這一傳統觀念提出了質疑。
