打呵欠有助于醒脑

 Latest research shows that yawning helps in keeping the brain cool, contradicting the popular belief that yawning promotes sleep and is a sign of tiredness.

Yawning involves opening the mouth involuntarily while taking a long, deep breath of air. It is commonly believed that people yawn as a result of drowsiness¹ or weariness because they need oxygen.

However, researchers at the University of Albany in New York said their experiments on 44 students showed that drawing in air helps cool the brain and helps it work more effectively.

They said that their experiments showed that raising or lowering oxygen and carbon dioxide levels in the blood did not produce that reaction.

Study participants were shown videos of people laughing, being neutral and yawning, and researchers counted how many times the volunteers responded to their own 'contagious² yawns,' reported the online edition of BBC News.

The researchers found that those who breathed through the nose rather than the mouth were less likely to yawn when watching a video of other people yawning. This was because vessels³ in the nasal cavity sent cool blood to the brain.

The same effect was found among those who held a cool pack to their forehead, whereas those who held a warm or room-temperature pack yawned while watching the video.

'Since yawning occurs when brain temperature rises, sending cool blood to the brain serves to maintain optimal⁴ levels of mental efficiency,' the authors wrote in the journal Evolutionary⁵ Psychology⁶.

最新研究表明，打呵欠有助于保持头脑清醒，这与“打呵欠促使人进入睡眠状态以及是疲倦的一种表现”的普遍看法正好相反。

打呵欠使人在不由自主张开嘴的同时，能长长的、深深的吸一口气。普遍看法认为，人们打呵欠是由于困乏或疲倦造成的，因为他们需要氧气。

然而，据纽约奥尔巴尼大学的研究人员介绍，他们对44名学生的实验表明，吸入空气有助于醒脑，从而使它更为有效的工作。

研究人员称，实验表明，提高或降低血液中氧气和二氧化碳的含量不会导致那种反应。

据BBC新闻网报道，研究人员先让实验对象观看人们大笑、正常状态以及打呵欠的视频，然后计算出志愿者“传染性打呵欠”的次数。

研究人员发现，在看别人打呵欠的视频时，用鼻子呼吸的人比用口腔呼吸的人打呵欠的几率要小。这是因为鼻腔里的血管将温度较低的血液送到了脑部。

将冰袋敷在前额上也能起到类似的效果，而在观看视频时用暖水袋或室温水袋敷在额头上的人却无法避免打呵欠。

这份在《进化生理学》上发表的研究报告提到，“由于脑部温度上升时就会打呵欠，所以将低温血液送至大脑能够保持脑部效率的最佳水平。”

1 drowsiness   

n.睡意；嗜睡

参考例句：

• A feeling of drowsiness crept over him. 一种昏昏欲睡的感觉逐渐袭扰着他。 来自《简明英汉词典》
• This decision reached, he finally felt a placid drowsiness steal over him. 想到这，来了一点平安的睡意。 来自汉英文学 - 骆驼祥子

2 contagious   

adj.传染性的，有感染力的

参考例句：

• It's a highly contagious infection.这种病极易传染。
• He's got a contagious laugh.他的笑富有感染力。

3 vessels   

n.血管( vessel的名词复数 )；船；容器；（具有特殊品质或接受特殊品质的）人

参考例句：

• The river is navigable by vessels of up to 90 tons. 90 吨以下的船只可以从这条河通过。 来自《简明英汉词典》
• All modern vessels of any size are fitted with radar installations. 所有现代化船只都有雷达装置。 来自《现代汉英综合大词典》

4 optimal   

adj.最适宜的；最理想的；最令人满意的

参考例句：

• What is the optimal mix of private and public property rights in natural resources?私人和国家的自然资源产权的最适宜的组合是什么？
• Optimal path planning is a key link for the sailing contest.帆船最优行驶路径规划是帆船比赛取胜的关键环节。

5 evolutionary   

adj.进化的；演化的，演变的；[生]进化论的

参考例句：

• Life has its own evolutionary process.生命有其自身的进化过程。
• These are fascinating questions to be resolved by the evolutionary studies of plants.这些十分吸引人的问题将在研究植物进化过程中得以解决。

6 psychology   

n.心理，心理学，心理状态

参考例句：

• She has a background in child psychology.她受过儿童心理学的教育。
• He studied philosophy and psychology at Cambridge.他在剑桥大学学习哲学和心理学。