○  TED英语演讲稿：我们为什么要睡觉  ○

not least the biological clock. The biological clock tells us when it's good to be up, when it's good to be asleep, and what that structure does is interact with a whole raft of other areas within the hypothalamus, the lateral hypothalamus, the ventrolateral preoptic nuclei. All of those combine, and they send projections down to the brain stem here. The brain stem then projects forward and bathes the cortex, this wonderfully wrinkly bit over here, with neurotransmitters that keep us awake and essentially provide us with our consciousness. So sleep arises from a whole raft of different interactions within the brain, and essentially, sleep is turned on and off as a result of a range of

　　Okay. So where have we got to? We've said that sleep is complicated and it takes 32 years of our life. But what I haven't explained is what sleep is about. So why do we sleep? And it won't surprise any of you that, of course, the scientists, we don't have a consensus. There are dozens of different ideas about why we sleep, and I'm going to outline three of those.

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