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 drowsiness 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 'contagious 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 vessels 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 optimal levels of mental efficiency,' the authors wrote in the journal Evolutionary  Psycology.

    最新研究表明，打呵欠有助于保持頭腦清醒，這與“打呵欠促使人進入睡眠狀態以及是疲倦的一種表現”的普遍看法正好相反。
    
    打呵欠使人在不由自主張開嘴的同時，能長長的、深深的吸一口氣。普遍看法認為，人們打呵欠是由于困乏或疲倦造成的，因為他們需要氧氣。

    然而，據紐約奧爾巴尼大學的研究人員介紹，他們對44名學生的實驗表明，吸入空氣有助于醒腦，從而使它更為有效的工作。

    研究人員稱，實驗表明，提高或降低血液中氧氣和二氧化碳的含量不會導致那種反應。

    據BBC新聞網報道，研究人員先讓實驗對象觀看人們大笑、正常狀態以及打呵欠的視頻，然后計算出志愿者“傳染性打呵欠”的次數。

    研究人員發現，在看別人打呵欠的視頻時，用鼻子呼吸的人比用口腔呼吸的人打呵欠的幾率要小。這是因為鼻腔里的血管將溫度較低的血液送到了腦部。

    將冰袋敷在前額上也能起到類似的效果，而在觀看視頻時用暖水袋或室溫水袋敷在額頭上的人卻無法避免打呵欠。

    這份在《進化生理學》上發表的研究報告提到，“由于腦部溫度上升時就會打呵欠，所以將低溫血液送至大腦能夠保持腦部效率的最佳水平。”