The Science Of Sleep

This segment was originally broadcast on March 13, 2008. It was updated on June 12, 2008.

Human beings spend on average one third of our lives asleep. We know we need to sleep, but most of us have never really given a whole lot of thought to why.

Why do we spend seven or eight hours a night immobile and unconscious? What really happens inside our brains and bodies while we're sleeping?

As correspondent Lesley Stahl first reported this spring, it's one of the biggest unanswered questions in all of science, which is why researchers all over the country are doing studies, and coming up with some new, intriguing discoveries.

"Well, that's been one of the long-standing theories. But I think what we're starting to understand is that sleep serves a whole constellation of functions, plural," Walker explains.

One thing that's clear, says Walker, is that sleep is critical. In a series of studies done back in the 1980s, rats were kept awake indefinitely. After just five days, they started dying.

Walker says they started dying from sleep deprivation. "In fact, sleep is as essential as food because they will die just about as quick from food deprivation as sleep deprivation. So, it's that necessary," he says.

And it's not just rats: every animal studied so far needs sleep, from the elephant right down to the fruit fly. But that's as far as the similarities go. Some animals sleep 20 hours a day, others only two or three. And still others sleep with half their brains at a time, all making it hard to figure out what exactly it is about sleep that makes it so essential, and that, in terms of evolution, makes it worth the risks.

"You wonder why we developed this if survival is the whole point. Because you're completely vulnerable when you're lying there," Stahl points out.

"Whatever the function of sleep, or the functions of sleep are, they seem to be so important that evolution is willing to put us in that place of potential danger by losing consciousness. It would be the biggest evolutionary mistake if sleep does not serve some critical function," Walker says.

One of the most exciting new discoveries in the field of sleep research involves learning and memory.

Five college students were subjects in one of Walker's studies, and they had been awake for more than 24 hours. He has found that students like these do 40 percent worse memorizing lists of words after a night without sleep. But he has discovered something far more revolutionary about what happens when we do sleep.

"Sleep, we've been finding, actually can enhance your memories, so that you'll come back the next day even better than where you were the day before," Walker tells Stahl.

To prove it, Walker put Stahl through a test he's given to more than 400 study subjects. Stahl had to type a series of numbers - 4, 1, 3, 2, 4 - over and over again with her left hand, making a new physical memory.

Some of Walker's subjects learned this sequence in the morning, then were tested 12 hours later to see how well they had learned. Their performance remained essentially the same. But others learned it late in the day, then were re-tested after a night of sleep. Their performance, as well as Stahl's, actually improved by at least 20 to 30 percent.

"So, it seems to be that practice does not quite make perfect; it's practice with a night of sleep that makes perfect," Walker says. "It's this odd notion that we all think in Western civilization that we have to stay awake to get more done. And I think that's simply not true. In fact, I think if you have a good night of sleep, what you'll find is that you can get more done than if you simply stay awake."

But what if you do sleep, just not enough?

That's the focus of an NIH-funded study at the University of Pennsylvania's School of Medicine, where four paid volunteers get wired up with electrodes and spend a week and a half sequestered in a dimly lit hospital suite. They have to stay awake until 4 a.m., then are woken up at 8 a.m. for five nights in a row. Then they're given tests to measure the effects of what's called "chronic partial sleep deprivation."

"So what are you finding? What kind of effect does just four hours a night have?" Stahl asks David Dinges, the scientist in charge of the Penn study.

"Well, the first finding, and it stunned us, was there's a cumulative impairment that develops in your ability to think fast, to react quickly, to remember things. And it starts right away," Dinges says. "A single night at four hours or five hours or even six, can in most people, begin to show affects in your attention and your memory and the speed with which you think. A second night it gets worse. A third night worse. Each day adds an additional burden or deficit to your cognitive ability."

"I'm stunned by you saying one night of just four or five hours sleep, and your ability to function is already hurt," Stahl remarks.

"But remember, we're not allowing caffeine, and we're not allowing physical activity and bright light. And for most of us, probably a day or two or so, you can get by taking these, what we call the counter measures, right? But, at some point what these studies show is the impairments get so bad, that there's little to no rescue possible without getting more sleep," Dinges says.

Dinges told 60 Minutes that his subjects, like a young French woman named Hacina, get to where it seems like they're moving through molasses.

"So, overall, how do you think not having enough sleep for five nights has affected you?" Stahl asked Hacina.

"Well, my - I- I'm quiet - quieter, definitely," she replied.

"And - and - uh- what else did you ask?" Hacina asked after a long pause, seeming confused.

The testing for alertness and reaction time has real-world relevance. Virginia Tech's Transportation Institute did a study of what causes car crashes. They got 241 volunteers to agree to have their cars wired with five cameras each. Over a year's time they found that driving drowsy was the riskiest behavior of all.

"You only need two seconds to have a lapse, in driving a car at 60 miles an hour, to drift completely out lane," Dinges says. "You're off the road in four seconds. And those kinds of lapses and slowed reaction times begin to appear fairly early."

The lapses are called "micro-sleeps," and can even occur when people have their eyes open.

What about turning up the radio, or opening the window to lower the temperature?

"Studies show that all of that stuff people tend to do - slapping themselves in the face, rolling the window down, radio up, singing - they're convinced it helps. But it's only a matter of seconds or minutes. And you can have a sudden sleep attack right in the midst of doing that," Dinges says.

And it's not just driving. Dinges has examined, sometimes as an expert witness, the role of inadequate sleep in some of the world's most well-known accidents.

He thinks inadequate sleep may have contributed to the Exxon Valdez oil spill, Chernobyl, the Three Mile Island disaster and the 2003 Staten Island ferry crash.

60 Minutes checked. The Exxon Valdez spill happened after midnight with a man at the helm who'd slept only four hours the night before; Chernobyl and Three Mile Island also occurred late at night and involved human error. And the assistant captain who crashed the Staten Island ferry into a pier, killing 11, admitted that he felt exhausted before the accident.

"Many people want something associated with morals or management or…alcohol," Dinges remarks. "Those are far more glamorous. But, in reality, many of these disasters involve poor judgments and slowed reactions at a time when people were basically tired and made not complicated mistakes. Simple ones. And that is the hallmark of sleep deprivation."

Hacina, the sleep-deprived French woman in the Penn study, thought she was maybe alert enough to give Stahl a lift.

"What really struck me is that she didn't know how impaired she was. It was clear, but she didn't know," Stahl remarks.

"That has been a finding in all of our studies. They tell you they've adapted. They're okay," Dinges says.

Dinges says people who are chronically sleep deprived, like people who've had too much to drink, often have no sense of their limitations. They believe they've trained themselves. "I think it's a convenient belief. For the millions of people who don't get enough sleep because their commute to work is too long, or they spend too many hours at work, or they just want this lifestyle of go, go, go, it's convenient to say, 'I've learned to live without sleep.' But you bring 'em into the laboratory - and we have an open challenge to any CEO or anyone in the world, come into the laboratory - we don't see this adaptation," he says.

One thing sleep researchers do see is that their sleep-deprived volunteers often have mood swings: they get short-tempered, then become almost giddy, sometimes within seconds.

"We took a group of young college undergraduates and we deprived them of sleep for about 35 hours straight. And then we placed them inside a MRI scanner and we showed them increasingly negative and disturbing images," says Matthew Walker, who devised a study to look at what was going on inside their brains. "And what we found was that in those people who had a good night of sleep, the control group, they showed a nice, modest, controlled response in their emotional centers of the brain."

"But, when we looked in the sleep deprived subjects, instead, what we found is a hyperactive brain response," he says.

And what's more, in the sleep-deprived subjects, Walker discovered a disconnect between that over-reacting amygdala (a region of the brain) and the brain's frontal lobe, the region that controls rational thought and decision-making, meaning that the subjects' emotional responses were not being kept in check by the more logical seat of reasoning. It's a problem also found in people with psychiatric disorders.

"So you're saying that you take someone with a severe mental disorder and a person without that disorder, but deprive them of sleep, and the brain scan will look similar?" Stahl asks.

"Their pattern of brain activity was not dissimilar. So I think what it forces us to do really now is to appreciate more significantly the role that sleep may be playing in mental health and in psychiatric diseases. And I think that could be one of the futures of the field of sleep research," Walker replies.

Walker says most of us need seven and a half to eight hours of sleep every night.

By almost all measures, we are sleeping less than ever before. In 1960, a survey by the American Cancer Society asked one million Americans how much sleep they were getting a night. The median answer was eight hours. Today that number has fallen to 6.7 hours-a decrease of more than 15 percent in less than a lifetime. And from what the scientists 60 Minutes met are finding, we may be putting ourselves in a perilous situation.

Eve Van Cauter, an endocrinologist at the University of Chicago School of Medicine, studies the effect of sleep on the body. At her lab, healthy, young volunteers like Jonathan Mrock are paid to come one at a time and have virtually every system in their bodies monitored while their sleep is interfered with.

"We did a study where we restricted sleep to four hours per night for six nights," Van Cauter explains. "And we noticed that they were already in a pre-diabetic state. And so, that was a big finding."

The study's subjects were on the road to diabetes in just six days, and that's not all - they were also hungry. Van Cauter has made a radical discovery: that lack of sleep may be contributing to the epidemic of obesity in this country through the work of a hormone called leptin that tells your brain when you're full.

"We observed that the volunteers, they actually had a drop in leptin levels," Van Cauter explains. "Leptin was telling the brain, 'Time to eat. We need more food.'"

"Even though they'd eaten," Stahl remarks.

"But in fact they had plenty of food," Van Cauter agrees.

Several large-scale studies from all over the world have reported a link between short sleep times and obesity, as well as heart disease, high blood pressure, and stroke.

"I think it tells us that sleep deprivation is not a challenge for which biology has wired us. There's no other mammal that sleep deprives itself than the human. So it is read by our biology as a stress," Van Cauter says.

"You know, our attitude about sleep flies in the face of what you're saying. Because I think that 'You don't need as much sleep' is looked upon as something very positive," Stahl remarks.

"It's seen as a badge of honor," Van Cauter agrees. "But you know I find it amazing to see how many people are asleep within five minutes of boarding an airplane at 11 o'clock in the morning. You know, sit down and boom. It shouldn't happen. A normal adult shouldn't be falling asleep at 11 o'clock in the morning, minutes after sitting in a small, uncomfortable airplane seat. It just shows that, you know, people are exhausted."

Jonathan the volunteer hasn't been told exactly what is being tested during his stay at the lab. He just knows on day five that he's feeling kind of groggy.

He thinks it's the lights, but that's because they aren't telling him about the sounds. Unbeknownst to Jonathan, each night when he falls into what should be a restful slumber, he's actually entering an eight and a half hour battle. Jonathan's opponent is Dr. Esra Tasali, a colleague of Van Cauter, who is watching him and his brain waves from a small control room across the hall and blasting sounds through speakers on both sides of his bed.

In this experiment, the idea is not to interfere with the quantity of Jonathan's sleep but the quality. Soon after he falls asleep, Jonathan's body naturally wants to enter what's called "deep sleep," but Tasali is determined to stop him without waking him up. Every time his brain starts producing what are called "delta waves," indicating the start of deep sleep, she searches her arsenal of sounds and "attacks."

During a normal night, we cycle through different stages of sleep, progressing from light into deep sleep, then into REM (Rapid eye movement), or dream sleep, and back again. As we age, though, the amount of time we spend in deep sleep decreases.

Van Cauter and Tasali are investigating a novel theory that some of the health problems we typically associate with old age may in fact be caused by the loss of deep sleep.

"We lose deep sleep at a very early age. So a young, healthy person may have 100 minutes of deep sleep, and at 50 years old it may be as little as 20 minutes. So it really… goes down very quickly," Van Cauter explains.

Tasali's goal is to turn 19-year-old Jonathan, sleep-wise, into a 70-year-old.

The next morning - 346 sounds later - it's time for testing. Now Jonathan's going to have fat extracted from his body for analysis, go through a PET scan to see how his brain is metabolizing sugar, and between procedures, he's answering questions about how he feels. His doctors assure 60 Minutes that Jonathan will be fine once he goes back to his normal sleep routine, but after four nights without deep sleep they have found that, like prior study subjects, he is hungrier, less alert, and most importantly, his body is no longer able to metabolize sugar effectively, putting him temporarily at increased risk for Type 2 diabetes.

"We usually think of diabetes as something that's a disease of old age. But really it may be a disease of sleep deprivation," Stahl remarks.

"I would say that sleep deprivation may be a new risk factor for diabetes," Van Cauter says. "Not just aging, not just being overweight or obese, not just having a family history of diabetes, which are the three major risk factors. But this is an added one. And we have really an epidemic of diabetes now. And Type 2 diabetes is now occurring in children, in adolescents. And, you know, adolescents and children too are also being sleep deprived. Maybe high schoolers are amongst the most sleep deprived individuals in our society, because they have an enormous sleep need - nine to ten hours. Yet they sleep less than seven hours per night."

She says this research proves we all need to rethink what we consider essential for good health - that the diet and exercise formula also has to include sleep.

So if lack of sleep impacts our appetite, our metabolism, our memory, and how we age, is there anything it doesn't affect? How about sex? Scientist Scott McRobert at St. Joseph's University in Philadelphia is asking that very question, studying fruit flies.

Stahl watched as McRobert used a bizarre contraption to suck a male drosophila (fruit fly) out of a vial and put him into a little dish with a female.

McRobert gave Stahl a play-by-play of the action. "Okay. So now, the female's walking around the outside of the chamber," McRobert explains. "And the male's in the center. And you see he's orienting toward her, everywhere she goes."

"He's following her. If you watch closely, he'll touch her with his front legs. It's hard to see, but he will. And he'll sing. Here comes the song," McRobert says.

Flies sing, he tells Stahl, by lifting one wing to the side and vibrating it up and down.

McRobert is doing a study to see whether sleep-deprivation in fruit flies affects mating. The two flies in the dish had regular amounts of sleep. "And when he's in the presence of a sexually attractive female, he's just courting and doing almost nothing else," he says.

Eventually, the flies did mate.

But it was a different story when a pair of flies was brought together where the male had been sleep deprived.

"You can actually see the difference. He was courting a second ago. But he doesn't stay with her," McRobert points out.

McRobert told Stahl the sleep-deprived flies rarely if ever mate.

"Even though you're not sure how to make an analogy to men, if any are watching, nevertheless, this could be somewhat of a lesson," Stahl remarks.

"If you want to take this to the level of humans. And this is something that geneticists rarely do if they're smart. And I probably shouldn't do it either. But the take-home lesson is 'Get enough sleep,'" McRobert says. "I mean, the successful male drosophila is a drosophila that gets enough sleep."

So at least for now, it looks like we're stuck sleeping a third of our lives away.

"Humans love to keep asking, 'Can't we just get rid of sleep?' If you had a poll in the United States and said, 'If we could safely eliminate half of the time you sleep. And you wouldn't suffer any deficit, you'd be good to go.' We could just magically make sleep go away. How many people would want it? And I believe you'd find the population votes easily overwhelmingly for it," David Dinges predicts. "And yet I think the hedonic joy of sleeping and the need for sleep and how good it feels…I would have to say that consciousness, wake-consciousness is probably a bit overrated."

Asked if she thinks we're going to figure out a way to get along with less sleep, Eve Van Cauter tells Stahl, "I hope not."

"You don't think that's where research should put its effort?" Stahl asks.

"You know, Lesley, my impression is that sleep affects so many aspects of mental and physical function, that there's not going to be one magic bullet drug that will be able to compensate. Much better idea is simply to sleep an hour more," she says.

Produced By Shari Finkelstein