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 doze 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 dormant 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 drowsy” and then snap out of it “back to alertness” he says.

The aim of the research is to find out how this pre-sleep phase, when the eyes glaze, the attention wanders and the mind is lulled, could be linked to accidents and dangerous mistakes. This could happen during the day while at work. “If you're doing some boring task, you might be drowsy in this period. Small drift-offs can cause big problems,” says Mr Jangannathan. This is not just connected to safety concerns with driving, for example, but any task where concentration and decision making are important.

There are positive sides to this hypnagogic period too. Some experts think there is a connection to creativity and imagination. This is caused by a reduction in your inhibitions, which makes you more creative. You have more freedom to express yourself, and you're more willing to make mistakes. It certainly seems to support the old adage of sleeping on it to solve a problem.

Ultimately, there are hopes that research into brain activity during falling asleep and waking might help stroke victims who are trying to regain lost physical functions. That could well be a pipe dream. There are also research efforts underway to find ways to warn of the onset of sleep, identifying changes in eye movements or brain activity. These could have practical applications for tired people operating heavy machinery and may help ensure that when it comes to accidents, we're not caught napping.