每个人一生中大约有三分之一的时间都处于睡眠状态。一直以来，科学家对于人类为什么要睡觉，睡觉时大脑究竟处于什么状态等问题进行了多方面的深入研究。那么，当人类处于睡眠边缘状态时，身体里到底发生着什么变化？它又意味着什么？新的研究正在寻找这些答案。
How long does it take you to fall asleep? Are you out like a light as soon as your head hits the pillow, or does it take you more than a little time to doze1 off?
If the average night's sleep is eight hours, or a third of a day, then it means we spend around one third of our lives in this dormant2 state. Science already has reams of data on the brain's activity during sleep itself. Now, an international group of researchers at the University of Cambridge are researching that dopey state we all go through between wide awake and fast asleep.
This transitional period usually lasts between five and 20 minutes, says Sridhar Rajan Jagannathan, one of Cambridge's Gates Scholars. However, people exhibit a variety of behaviour within this time. For some, going to the land of nod is a smooth, quick journey, while others have more difficulty. They “begin to get drowsy3”
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