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RACHEL MARTIN, HOST:

We spend one-third of our lives sleeping. That's more time than we spend doing anything else, but we still don't know very much about sleep. So today, we're trying to answer some pretty basic yet complicated questions: Why do we sleep? Can we live without it, and how can we get more? Because let's face it, there are a lot of us out there who are not exactly sleeping soundly.

(SOUNDBITE OF MUSIC, CLOCK TICKING)

LISA HURST-CAIRNS: You're looking at your clock and it's - oh, 2:20, 2:30, 2:40; and you're doing the math. Now I've got three hours, or four hours, to sleep, and I'm going to be dead tired in the morning.

WILL PARKHURST: I started noticing in the morning that there'd be like, pretty much just crumbs on the ground next to my bed, and I'd have food next to my bed that I did not remember ever bringing to bed with me.

RAQUEL ZIC: I usually take Benadryl and melatonin. To get up at 2:30 in the morning, it's kind of a necessary evil.

PARKHURST: So I started off with a lot of ice cream. Cereal's pretty common. Pretzels, stuff like that; chips, crackers. For a while, I was eating a bunch of granola in my sleep.

(SOUNDBITE OF MUSIC)

HURST-CAIRNS: For so many years, I was like, fighting this, you know, inability to stay asleep. So every night, waking up and just kind of going, oh, no. Now, I only have like, four more hours; and I've got to do this and this and this the next day - and really, just getting in this like, anxious spiral.

(SOUNDBITE OF MUSIC, CLOCK TICKING)

MARTIN: That was Lisa Hurst-Cairns(ph), an insomniac from Minneapolis; Will Parkhurst(ph), a sleep eater from Austin, Texas; and ambulance driver Raquel Zic(ph), who has to wake up at 2:30 a.m. To better understand the mystery of sleep, we called up Dr. Matthew Walker. He's the principal investigator at the Sleep Lab at the University of California, Berkeley. Walker says after decades of sleep research, there are still some gaping holes.

MATTHEW WALKER: We still cannot give you, the public, a definitive answer to the question, why do we sleep? We've known the functions of the other three main biological drives - which are eating, drinking and reproducing. But this question of sleep still remains that archetypal mystery.

MARTIN: Is this a source of embarrassment at all, for people who do what you do; that you can't answer that fundamental question?

WALKER: Well, I think it's either an embarrassment, or it's an embarrassment of research question riches - because there have been so many great discoveries within science based on the revolution of sort of genetics and molecular biology. And sleep remains resistant to all of that, in terms of an answer. So it's a fantastically complex puzzle. And as a researcher, that's what you want. You don't want something where there's an easy answer.

MARTIN: So how do you define success in the field of sleep research?

WALKER: Yes. So, I think there's really two avenues of success metric, as it were. One of them is to try and answer those basic fundamental questions - you know, what are the benefits of sleep, and what is sleep doing? I think the other is upon knowing that, how can it help people? There are several things that we've been discovering that are critical. The first is the role of sleep in learning and memory. And now, there's really very good evidence that sleep is critical at almost all stages of memory formation, memory processing and long-term memory retention. And then secondly, we have more recently been discovering that sleep plays an intimate role in regulating our emotional well-being and our mental health.

MARTIN: We hear all the time that sleep is a state that perhaps opens different doors of our minds, our brains, and allows a greater sense of creativity. How is that so?

WALKER: Well, firstly, we've got wonderful anecdotes throughout history of sleep-inspired creativity. Paul McCartney apparently came up with lots of music, in dreams. Frankenstein, Mary Shelly's text - Dmitri Mendeleev came up with the creation of the periodic table of elements - the construction of that - by way of sleeping. Well, recently, we've been able to find evidence to statistically show that sleep can support that type of creative memory processing. And there seems to be some type of memory processing that's creative that starts take pieces of information that we've learned recently and starts trying to test the connections between that recent information and all of that information you've got stored in your brain.

So, it's almost like memory pinball. You're bouncing that information around. You're testing which connections to build. And I think when those types of processes start to happen in sleep, when we start to fuse things together that shouldn't normally go together, they cause marked advances in evolutionary fitness. And that's what we're starting to find in our science.

MARTIN: What happens when we don't sleep?

WALKER: A whole constellation of different brain and body functions start to deteriorate. You can't learn information as effectively. So, pulling the all-nighter is a very bad idea. Your brain is about 40 percent less effective without sleep in terms of absorbing new information. It's almost like a waterlogged sponge. Nothing more can be soaked up. But we also know that if you don't sleep after learning, you lose the chance to essentially hit the save button on that information. And that information isn't transferred into long-term memory. We also know, from an emotional perspective, that certain regions within the brain, deep within the brain, those regions become amplified in their emotional reactivity. So, you become excessively emotionally reactive and part of the reason is because your frontal brain - a part of the brain that we call the prefrontal cortex - that becomes impaired. And it normally helps regulate those deep emotional senses, so we don't become irrational, we don't become Neanderthal. But without sleep, that's exactly what seems to happen.

MARTIN: I've got kind of an evolutionary question for you. From one perspective you might think that sleep actually goes against some basic survival instincts. I mean, when we're sleeping we're not eating, we're not protecting ourselves from predators. Why would we need sleep? Why would we evolve to do this?

WALKER: From an evolutionary perspective, everything screams at us that sleep is the very worst thing that you could do. The fact that sleep has fought it way heroically through every step along the evolutionary pathway, what that tells us is that sleep is essential at the most basic of biological levels. And what we're finding now is that it was very smart because sleep serves so many wonderful beneficial functions that far outweigh those potential downsides to it.

MARTIN: Are you a good sleeper?

(LAUGHTER)

WALKER: Yes and no. Certainly, I will routinely get seven and a half to eight hours of sleep a night. The no part of the yes and no is because you sort of become the Woody Allen neurotic of the sleep world. So, you know, if I'm sort of lying in bed and I'm thinking, you know, I know all the biology behind sleep, I know what should be happening and I'm thinking, well, this neurochemical is being released, this part of my brain is not shutting down. And at that point of analysis, you're dead in the water for the next two hours, so...

MARTIN: So, you can't just drink warm milk or a shot of bourbon and call it a day. You...

WALKER: I wish, I wish. And certainly I should know bourbon is a bad idea. Alcohol is profoundly disruptive to sleep. It fragments your sleep and it prevents you from getting REM sleep. But I wish I could and, sadly, no.

(SOUNDBITE OF SONG, "LULLABY")

UNIDENTIFIED SINGER: (Singing) Lullaby and good night...

MARTIN: Matthew Walker. He is the principal investigator at the Sleep Lab at the University of California, Berkeley. Thank you so much for talking with us, Matthew.

WALKER: You're very welcome. Sleep well.

(SOUNDBITE OF SONG, "LULLABY")

UNIDENTIFIED SINGER: (Singing) (unintelligible) hold thy hand. If God wills...

MARTIN: You're listening to WEEKEND EDITION from NPR News.

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