Home » Why Do We Sleep by Russell Foster (Transcript)

Why Do We Sleep by Russell Foster (Transcript)

In this TED talk, Russell Foster, a circadian neuroscientist, shares three popular theories about why we sleep, busts some myths about how much sleep we need at different ages — and hints at some bold new uses of sleep as a predictor of mental health. [Full Profile]



Russell Foster – Circadian Neuroscientist

What I’d like to do today is talk about one of my favorite subjects, and that is the neuroscience of sleep.

Now, there is a sound — (sound of alarm clock) — aah, it worked — a sound that is desperately, desperately familiar to most of us, and of course it’s the sound of the alarm clock. And what that truly ghastly, awful sound does is stop the single most important behavioral experience that we have, and that’s sleep. If you’re an average sort of person, 36% of your life will be spent asleep, which means that if you live to 90, then 32 years will have been spent entirely asleep.

Now what that 32 years is telling us is that sleep at some level is important. And yet, for most of us, we don’t give sleep a second thought. We throw it away. We really just don’t think about sleep. And so what I’d like to do today is change your views, change your ideas and your thoughts about sleep. And the journey that I want to take you on, we need to start by going back in time.

Perception about sleep through history

“Enjoy the honey-heavy dew of slumber.” Any ideas who said that? Shakespeare’s Julius Caesar. Yes, let me give you a few more quotes. “O sleep, O gentle sleep, nature’s soft nurse, how have I frighted thee?” Shakespeare again, from — I won’t say it — the Scottish play. [Correction: Henry IV, Part 2] From the same time: “Sleep is the golden chain that ties health and our bodies together.” Extremely prophetic, by Thomas Dekker, another Elizabethan dramatist.

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But if we jump forward 400 years, the tone about sleep changes somewhat. This is from Thomas Edison, from the beginning of the 20th century. “Sleep is a criminal waste of time and a heritage from our cave days.” Bang. And if we also jump into the 1980s, some of you may remember that Margaret Thatcher was reported to have said, “Sleep is for wimps.” And of course the infamous — what was his name? — the infamous Gordon Gekko from “Wall Street” said, “Money never sleeps.”

What do we do in the 20th century about sleep?

Well, of course, we use Thomas Edison’s light bulb to invade the night, and we occupied the dark, and in the process of this occupation, we’ve treated sleep as an illness, almost. We’ve treated it as an enemy. At most now, I suppose, we tolerate the need for sleep, and at worst perhaps many of us think of sleep as an illness that needs some sort of a cure. And our ignorance about sleep is really quite profound.

Why is it? Why do we abandon sleep in our thoughts? Well, it’s because you don’t do anything much while you’re asleep, it seems. You don’t eat. You don’t drink. And you don’t have sex. Well, most of us anyway. And so therefore it’s — Sorry. It’s a complete waste of time, right? Wrong. Actually, sleep is an incredibly important part of our biology, and neuroscientists are beginning to explain why it’s so very important. So let’s move to the brain.


Now, here we have a brain. This is donated by a social scientist, and they said they didn’t know what it was, or indeed how to use it, so — Sorry. So I borrowed it. I don’t think they noticed. Okay.

The point I’m trying to make is that when you’re asleep, this thing doesn’t shut down. In fact, some areas of the brain are actually more active during the sleep state than during the wake state. The other thing that’s really important about sleep is that it doesn’t arise from a single structure within the brain, but is to some extent a network property, and if we flip the brain on its back — I love this little bit of spinal cord here — this bit here is the hypothalamus, and right under there is a whole raft of interesting structures, not least the biological clock.

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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 interactions in here.

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.

Restoration Idea

The first is sort of the restoration idea, and it’s somewhat intuitive. Essentially, all the stuff we’ve burned up during the day, we restore, we replace, we rebuild during the night. And indeed, as an explanation, it goes back to Aristotle, so that’s, what, 2,300 years ago. It’s gone in and out of fashion. It’s fashionable at the moment because what’s been shown is that within the brain, a whole raft of genes have been shown to be turned on only during sleep, and those genes are associated with restoration and metabolic pathways. So there’s good evidence for the whole restoration hypothesis.

What about energy conservation? Again, perhaps intuitive. You essentially sleep to save calories. Now, when you do the sums, though, it doesn’t really pan out. If you compare an individual who has slept at night, or stayed awake and hasn’t moved very much, the energy saving of sleeping is about 110 calories a night. Now, that’s the equivalent of a hot dog bun. Now, I would say that a hot dog bun is kind of a meager return for such a complicated and demanding behavior as sleep. So I’m less convinced by the energy conservation idea.

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