We most associate yawning with boredom or being sleepy, but new research suggests it can be good for your health—by cooling down your brain.

　　Scientists at Princeton University found a big yawn can regulate the temperature of the brain and prevent over-heating.

　　During winter, Professor Andrew Gallup and his team asked 80 random pedestrians to look at images of people yawning and then recorded whether they yawned in response. They then performed the same trial in the summer.

　　The researchers found that half of the participants yawned in winter while only a quarter yawned in summer. You may think people would tend to cool the brain by yawning more in summer. But according to the theory, yawning cools the brain via a heat exchange with cooler air. This system therefore wouldn't work on a scorching summer's day.

　　Professor Gallup said: "Yawning should be suppressed—in ambient temperatures exceeding body temperature because taking a deep inhalation of air would not promote cooling.

　　He also suggested that this is the first study to show that yawning frequency varies from season to season. It could help explain why humans become confused and disorientated in extreme heat as the brain has limited ways of cooling itself down.

　　The research is published in the journal Frontiers in Evolutionary Neuroscience.

　　据英国《每日邮报》9月20日报道，人们把多把打哈欠和无聊与瞌睡联系在一起，但一项新研究表明，打哈欠可以给人脑“降温”，有益健康。

　　普林斯顿大学的科学家发现，打一个大大哈欠可以调节人脑温度，避免人脑过热。

　　安德鲁•盖洛普教授和他的团队在冬天随机测试了80名路人，让他们看关于人们打哈欠的图像，记录他们是否以打哈欠回应，他们在夏天也做了相同的试验。

　　研究人员发现，在冬天，一半参与者都会打哈欠，而在夏天打哈欠的受试者只有25%。也许人们会认为，人在夏天时更倾向于给脑子降温，但是，根据该理论，打哈欠得通过和较冷的空气进行热传导才能降低人脑温度。因此，该系统无法在闷热的夏天发挥作用。

　　盖洛普教授说：“当周围温度超过人体温度时，深吸空气并不能帮助降温，打哈欠也就会受到抑制。”

　　他还表示，该研究表明，打哈欠的频率会根据季节而变化，这能够帮助人们解释人脑降温途径受限时，会变得困惑和茫然的原因。

　　该研究发表在《进化神经系统前沿》杂志上。