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ОглавлениеBrain Rule #3
Sleep well, think well.
IT’S NOT THE MOST comfortable way to raise funds for a major American charity. In 1959, New York disk jockey Peter Tripp decided that he would stay awake for 200 straight hours. He got into a glass booth in the most visible place possible in New York—Times Square—and rigged up the radio so that he could broadcast his show. He even allowed scientists (and, wisely, medical professionals) to observe and measure his behavior as he descended into sleeplessness. One of those scientists was famed sleep researcher William Dement. For the first 72 hours, everything seemed fine with Tripp. He gave his normal three-hour show with humor and professional aplomb. Then things changed. Tripp became rude and offensive to the people around him. Hallucinations set in. The researchers testing his cognitive skills halfway through found he could no longer complete certain mental skill tests. At the 120-hour mark—five days in—Tripp showed real signs of mental impairment, which would only worsen with time. Dement described Tripp’s behavior toward the end of the adventure: “The disk jockey developed an acute paranoid psychosis during the nighttime hours, accompanied at times by auditory hallucination. He believed that unknown adversaries were attempting to slip drugs into his food and beverages in order to put him to sleep.” At the 200-hour mark—more than eight days—Tripp was done. Presumably, he went to bed and stayed there for a long time.
Some unfortunate souls don’t have the luxury of experimenting with sleep deprivation. They become suddenly and permanently incapable of ever going to sleep again. Only about 20 families in the world suffer from Fatal Familial Insomnia, making it one of the rarest human genetic disorders that exists. That rarity is a blessing, because the disease follows a course straight through mental-health hell. In middle to late adulthood, the person begins to experience fevers, tremors, and profuse sweating. As the insomnia becomes permanent, these symptoms are accompanied by increasingly uncontrollable muscular jerks and tics. The person soon experiences crushing feelings of depression and anxiety. He or she becomes psychotic. Finally, mercifully, the patient slips into a coma and dies.
So we know bad things happen when we don’t sleep. The puzzle is that, from an evolutionary standpoint, bad things also could happen when we do sleep. Because the body goes into a human version of micro-hibernation, sleep makes us exquisitely vulnerable to predators. Indeed, deliberately going off to dreamland unprotected in the middle of a bunch of hostile hunters (such as leopards, our evolutionary roommates in eastern Africa) seems like a plan dreamed up by our worst enemies. There must be something terribly important we need to accomplish during sleep if we are willing to take such risks in order to get it. Exactly what is it that is so darned important?
To begin to understand why we spend a walloping one-third of our time on this planet sleeping, let’s peer in on what the brain is doing while we sleep.
You call this rest?
If you ever get a chance to listen in on someone’s brain while its owner is slumbering, you’ll have to get over your disbelief. The brain does not appear to be asleep at all. Rather, it is almost unbelievably active during “rest,” with legions of neurons crackling electrical commands to one another in constantly shifting, extremely active patterns. In fact, the only time you can observe a real resting period for the brain—where the amount of energy consumed is less than during a similar awake period—is during the phase called non-REM sleep. But that takes up only about 20 percent of the total sleep cycle. This is why researchers early on began to disabuse themselves of the notion that the reason we rest is so that we can rest. When we are asleep, the brain is not resting at all. Even so, most people report that sleep is powerfully restorative, and they point to the fact that if they don’t get enough sleep, they don’t think as well the next day. That is measurably true, as we shall see shortly. And so we find ourselves in a quandary: Given the amount of energy the brain is using, it seems impossible that you could receive anything approaching mental rest and restoration during sleep.
Two scientists made substantial early contributions to our understanding of what the brain is doing while we sleep. Dement, who studied sleepless Peter Tripp, is a white-haired man with a broad smile who at this writing is in his late 80s. He says pithy things about our slumbering habits, such as “Dreaming permits each and every one of us to be quietly and safely insane every night of our lives.” Dement’s mentor, a gifted researcher named Nathaniel Kleitman, gave him many of his initial insights. If Dement can be considered the father of sleep research, Kleitman certainly could qualify as its grandfather. An intense Russian man with bushy eyebrows, Kleitman may be best noted for his willingness to experiment not only on himself but also on his children. When it appeared that a colleague of his had discovered rapid eye movement (REM) sleep, Kleitman promptly volunteered his daughter for experimentation, and she just as promptly confirmed the finding. He also persuaded a colleague to live with him underground to see what would happen to their sleep cycles without the influence of light and social cues. Here are some of the things Dement and Kleitman discovered about sleep.
Sleep is a battle
Like soldiers on a battlefield, we have two powerful and opposing drives locked in vicious, biological combat. The armies, each made of legions of brain cells and biochemicals, have very different agendas. Though localized in the head, the theater of operations for these armies engulfs every corner of the body. The war they are waging has some interesting rules. First, these forces are engaged not just during the night, while we sleep, but also during the day, while we are awake. Second, they are doomed to a combat schedule in which each army sequentially wins one battle, then promptly loses the next battle, then quickly wins the next and so on, cycling through this win/loss column every day and every night. Third, neither army ever claims final victory. This incessant engagement is referred to as the “opponent process” model. It results in the waking and sleeping modes all humans cycle through every day (and night) of our lives.
One army is composed of neurons, hormones, and various other chemicals that do everything in their power to keep you awake. This army is called the circadian arousal system (often simply called “process C”). If this army had its way, you would stay up all the time. It is opposed by an equally powerful army, also made of brain cells, hormones, and various chemicals. These combatants do everything in their power to put you to sleep. They are termed the homeostatic sleep drive (“process S”). If this army had its way, you would go to sleep and never wake up. These drives define for us both the amount of sleep we need and the amount of sleep we get. Stated formally, process S maintains the duration and intensity of sleep, while process C determines the tendency and timing of the need to go to sleep.
It is a paradoxical war. The longer one army controls the field, for example, the more likely it is to lose the battle. It’s almost as if each army becomes exhausted from having its way and eventually waves a temporary white flag. Indeed, the longer you are awake (the victorious process C doing victory laps around your head), the greater the probability becomes that the circadian arousal system will cede the field to its opponent. You then go to sleep. For most people, this act of capitulation comes after about 16 hours of active consciousness. This will occur, Kleitman found, even if you are living in a cave.
Conversely, the longer you are asleep (the triumphant process S now doing the heady victory laps), the greater the probability becomes that the homeostatic sleep drive will similarly cede the field to its opponent, which is, of course, the drive to keep you awake. The result of this surrender is that you wake up. For most people, the length of time prior to capitulation is about half of its opponent’s, about eight hours of blissful sleep. And this also will occur even if you are living in a cave.
Such dynamic tension is a normal—even critical—part of our daily lives. In fact, the circadian arousal system and the homeostatic sleep drive are locked in a cycle of victory and surrender so predictable, you can graph it.
In one of Kleitman’s most interesting experiments, he and a colleague spent an entire month living 1,300 feet underground in Mammoth Cave in Kentucky. Free of sunlight and daily schedules, Kleitman could find out whether the routines of wakefulness and sleep cycled themselves automatically through the human body. His experiment provided the first real hint that such an automatic device did exist in our bodies. Indeed, we now know that the body possesses a series of internal clocks, all controlled by discrete regions in the brain, providing a regular rhythmic schedule to our waking and sleeping experiences. This is surprisingly similar to the buzzing of a wristwatch’s internal quartz crystal. An area of the brain called the suprachiasmatic nucleus appears to contain just such a timing device. Of course, we have not been characterizing these pulsing rhythms as a benign wristwatch. We have been characterizing them as a war. One of Kleitman and Dement’s greatest contributions was to show that this nearly automatic rhythm occurs as a result of the continuous conflict between two opposing forces.
Are you a lark, owl, or hummingbird?
Each of us wages this war on a slightly different schedule. The late advice columnist Ann Landers apparently would take her phone off the hook between 1:00 a.m. and 10:00 a.m. Why? This was the time she normally slept. “No one’s going to call me,” she said, “until I’m ready.” The cartoonist Scott Adams, creator of the comic strip Dilbert, never would think of starting his day at 10:00 a.m. “I’m quite tuned into my rhythms,” he told the authors of The Body Clock Guide to Better Health. “I never try to do any creating past noon. … I do the strip from 6:00 to 7:00 a.m.” Here we have two creative and well-accomplished professionals, one who starts working just as the other’s workday is finished.
About one in 10 of us is like Dilbert’s Adams. The scientific literature calls such people larks (more palatable than the proper term, “early chronotype”). In general, larks report being most alert around noon and feel most productive at work a few hours before they eat lunch. They don’t need an alarm clock, because they invariably get up before the alarm rings—often before 6:00 a.m. Larks cheerfully report their favorite mealtime as breakfast and generally consume much less coffee than non-larks. Getting increasingly drowsy in the early evening, most larks go to bed (or want to go to bed) around 9:00 p.m.
Larks are incomprehensible to the one in 10 humans who lie at the other extreme of the sleep spectrum: “late chronotypes,” or owls. In general, owls report being most alert around 6:00 p.m., experiencing their most productive work times in the late evening. They rarely want to go to bed before 3:00 a.m. Owls invariably need an alarm clock to get them up in the morning, with extreme owls requiring multiple alarms to ensure arousal. Indeed, if owls had their druthers, most would not wake up much before 10:00 a.m. Not surprisingly, late chronotypes report their favorite mealtime as dinner, and they would drink gallons of coffee all day long to prop themselves up at work if given the opportunity. If it sounds to you as though owls do not sleep as well as larks in American society, you are right on the money. Indeed, late chronotypes usually accumulate a massive “sleep debt” as they go through life.
Whether lark or owl, researchers think these patterns are detectable in early childhood and burned into genes that govern our sleep/wake cycle. At least one study shows that if Mom or Dad is a lark, half of their kids will be, too. Larks and owls, though, cover only about 20 percent of the population. The rest of us are called hummingbirds. True to the idea of a continuum, some hummingbirds are more owlish, some are more larkish, and some are in between.
Nappin’ in the free world
It must have taken some getting used to, if you were a staffer in the socially conservative early 1960s. Lyndon Baines Johnson, 36th president of the United States and leader of the free world, routinely closed the door to his office in the midafternoon and put on his pajamas. He then proceeded to take a 30-minute nap. Rising refreshed, he would then resume his role as commander in chief. Such presidential behavior might seem downright weird. But if you asked a sleep researcher like Dement, his response might surprise you: It was LBJ who was acting normally. The rest of us, who refuse to bring our pajamas to work, are the abnormal ones.
LBJ was responding to something experienced by nearly everyone on the planet. It goes by many names—the midday yawn, the post-lunch dip, the afternoon “sleepies.” We’ll call it the nap zone, a period of time in the midafternoon when we experience transient sleepiness. It can be nearly impossible to get anything done during this time, and if you attempt to push through, which is what most of us do, you can spend much of your afternoon fighting a gnawing tiredness. It’s a fight because the brain really wants to take a nap and doesn’t care what its owner is doing. The concept of “siesta,” institutionalized in many other cultures, may have come as an explicit reaction to the nap zone.
At first, scientists didn’t believe the nap zone existed except as an artifact of sleep deprivation. That has changed. We now know that some people feel it more intensely than others. We know it is not related to a big lunch (although a big lunch, especially one loaded with carbs, can greatly increase its intensity). We also know that when you chart the process S curve and process C curve, you can see that they flatline in the same place—in the afternoon. The biochemical battle reaches a climactic stalemate. An equal tension now exists between the two drives, which extracts a great deal of energy to maintain. Some researchers, though not all, think this equanimity in tension drives the need to nap. Some think that a long sleep at night and a short midday nap represent default human sleep behavior, that it is part of our evolutionary history.
Regardless of the cause, the nap zone matters, because our brains don’t work as well during it. If you are a public speaker, you already know it is darn near fatal to give a talk in the midafternoon. The nap zone also is literally fatal: More traffic accidents occur during it than at any other time of the day.
If you embrace the need to nap rather than pushing through, as LBJ found, your brain will work better afterward. One NASA study showed that a 26-minute nap reduced a flight crew’s lapses in awareness by 34 percent, compared to a control group who didn’t nap. Nappers also saw a 16 percent improvement in reaction times. And their performance stayed consistent throughout the day rather than dropping off at the end of a flight or at night. (The flight crew was given a 40-minute break, it took about six minutes for people to fall asleep, and the average nap lasted 26 minutes.) Another study showed that a 45-minute nap produces a similar boost in cognitive performance, a boost lasting more than six hours. Also, napping for 30 minutes before pulling an all-nighter keeps your mind sharper in the wee hours.
What happens if we don’t get enough sleep
Given our understanding of how and when we sleep, you might expect that scientists would have an answer to the question of how much sleep we need. Indeed, they do. The answer is: We don’t know. You did not read that wrong. After all of these centuries of experience with sleep, we still don’t know how much of the stuff people actually need. Generalizations don’t work. When you dig into the data on humans, what you find is not remarkable uniformity but remarkable individuality. To make matters worse, sleep schedules are unbelievably dynamic. They change with age. They change with gender. They change depending upon whether or not you are pregnant, and whether or not you are going through puberty. One must take into account so many variables that it almost feels as though we’ve asked the wrong question.
So let’s invert the query. How much sleep don’t you need? In other words, what are the numbers that disrupt normal function?
Sleep loss = brain drain
One study showed that a highly successful student can be set up for a precipitous academic fall just by getting less than seven hours of sleep a night. Take an A student used to scoring in the top 10 percent of virtually anything she does. If she gets just under seven hours of sleep on weekdays, and about 40 minutes more on weekends, her scores will begin to match the scores of the bottom 9 percent of individuals who are getting enough sleep. Cumulative losses during the week add up to cumulative deficits during the weekend—and, if not paid for, that sleep debt will be carried into the next week.
Another study followed soldiers responsible for operating complex military hardware. One night’s loss of sleep resulted in about a 30 percent loss in overall cognitive skill, with a subsequent drop in performance. Bump that to two nights of sleep loss, and the loss in cognitive skill doubles to 60 percent.
Other studies showed that when sleep was restricted to six hours or less per night for just five nights, cognitive performance matched that of a person suffering from 48 hours of continual sleep deprivation.
What do these data tell us? That some people need at least seven hours of sleep a night. And that some people need at least six hours of sleep a night. On the other hand, you may have heard of people who seem to need only four or five hours of sleep. They are referred to as suffering from “healthy insomnia.” Essentially, it comes down to whatever amount of sleep is right for you. When robbed of that, bad things really do happen to your brain.
Sleep loss takes a toll on the body, too—on functions that do not at first blush seem associated with sleep. When people become sleep deprived, for example, their body’s ability to utilize the food they are consuming falls by about one-third. The ability to make insulin and to extract energy from the brain’s favorite source, glucose, begins to fail miserably. At the same time, you find a marked need to have more of it, because the body’s stress hormone levels begin to rise in an increasingly deregulated fashion. If you keep up the behavior, you appear to accelerate parts of the aging process. For example, if healthy 30-year-olds are sleep deprived for six days (averaging, in this study, about four hours of sleep per night), parts of their body chemistry soon revert to that of a 60-year-old. And if they are allowed to recover, it will take them almost a week to get back to their 30-year-old systems.
Taken together, these studies show that sleep loss cripples thinking in just about every way you can measure thinking. Sleep loss hurts attention, executive function, working memory, mood, quantitative skills, logical reasoning ability, general math knowledge. Eventually, sleep loss affects manual dexterity, including fine motor control, and even gross motor movements, such as the ability to walk on a treadmill.
So what can a good night’s sleep do for us?
Sleep on it: benefits of a solid night’s rest
Dimitri Ivanovich Mendeleyev was your archetypal brilliant-but-mad-looking scientist. Hairy and opinionated, Mendeleyev possessed the lurking countenance of a Rasputin, the haunting eyes of Peter the Great, and the moral flexibility of both. He once threatened to commit suicide if a young lady didn’t marry him. She consented, which was quite illegal, because unbeknownst to the poor girl, Mendeleyev was already married. This trespass kept him out of the Russian Academy of Sciences for some time, which in hindsight may have been a bit rash, as Mendeleyev single-handedly systematized the entire science of chemistry. His Periodic Table of the Elements—a way of organizing every atom that had so far been discovered—was so prescient, it allowed room for all of the elements yet to be found and even predicted some of their properties.
But what’s most extraordinary is this: Mendeleyev says he came up with the idea in his sleep. Contemplating the nature of the universe while playing solitaire one evening, he nodded off. When he awoke, he knew how all of the atoms in the universe were organized, and he promptly created his famous table. Interestingly, he organized the atoms in repeating groups of seven, just the way you play solitaire.
Mendeleyev is hardly the only scientist who has reported feelings of inspiration after having slept. Is there something to the notion of “Let’s sleep on it”? Mountains of data say there is. A healthy night’s sleep can indeed boost learning significantly. Sleep scientists debate how we should define learning, and what exactly is improvement. But there are many examples of the phenomenon. One study stands out in particular.
Students were given a series of math problems and prepped with a method to solve them. The students weren’t told there was also an easier “shortcut” way to solve the problems, potentially discoverable while doing the exercise. The question was: Is there any way to jump-start, even speed up, the insight into the shortcut? The answer was yes, if you allow them to sleep on it. If you let 12 hours pass after the initial training and ask the students to do more problems, about 20 percent will have discovered the shortcut. But, if in that 12 hours you also allow eight or so hours of regular sleep, that figure triples to about 60 percent. No matter how many times the experiment is run, the sleep group consistently outperforms the non-sleep group about three to one.
Sleep also has been shown to enhance tasks that involve visual texture discrimination (the ability to pick out an object from an ocean of similar-looking objects), motor adaptations (improving movement skills), and motor sequence learning. The type of learning that appears to be most sensitive to sleep improvement is that which involves learning a procedure. Simply disrupt the night’s sleep at specific stages and retest in the morning, and you eliminate any overnight learning improvement. Clearly, for specific types of intellectual skill, sleep can be a great friend to learning.
Why we sleep
Consider the following true story of a successfully married, incredibly detail-oriented accountant. Even though dead asleep, he regularly gives financial reports to his wife all night long. Many of these reports come from the day’s activities. (Incidentally, if his wife wakes him up—which is often, because his financial broadcasts are loud—the accountant becomes amorous and wants to have sex.) Are we all organizing our previous experiences while we sleep? Could this not only explain all of the other data we have been discussing, but also provide the reason why we sleep?
To answer these questions, we turn to a group of researchers who left a bunch of wires stuck inside a rat’s brain—electrodes placed near individual neurons. The rat had just learned to negotiate a maze when it decided to take a nap. The wires were attached to a recording device, which happened to still be on. The device allows scientists to eavesdrop on the brain while it is talking to itself, something like an NSA phone tap. Even in a tiny rat’s brain, it is not unusual these days to listen in on the chattering of up to 500 neurons at once as they process information. So what are they all saying?
If you listen in while the rat is acquiring new information, like learning to navigate a maze, you soon will detect something extraordinary. A very discrete “maze-specific” pattern of electrical stimulation begins to emerge. Working something like the old Morse code, a series of neurons begin to crackle in a specifically timed sequence while the mouse is learning. Afterward, the rat will always fire off that same pattern whenever it travels through the maze. It appears to be an electrical representation of the rat’s new maze-navigating thought patterns (at least, as many as 500 electrodes can detect).
When the rat goes to sleep, its brain begins to replay the maze-pattern sequence. Reminiscent of our accountant, the animal’s brain repeats what it learned that day. Always executing the pattern in a specific stage of sleep, the rat repeats it over and over again—and much faster than during the day. The rate is so furious, the sequence is replayed thousands of times. If a mean graduate student decides to wake up the rat during this stage, called slow-wave sleep, something equally extraordinary is observed. The rat has trouble remembering the maze the next day. Quite literally, the rat seems to be consolidating the day’s learning the night after that learning occurred, and an interruption of that sleep disrupts the learning cycle.
This naturally caused researchers to ask whether the same was true for humans. The answer? Not only do we do such processing, but we do it in a more complex fashion. Like the rat, humans appear to replay certain learning experiences at night, during the slow-wave phase. Unlike the rat, more emotionally charged memories appear to replay at a different stage in the sleep cycle.
These findings represent a bombshell of an idea: Some kind of offline processing is occurring at night. Is it possible that the reason we need to sleep is simply to shut off the exterior world for a while, allowing us to divert more attention to our cognitive interiors? Is it possible that the reason we need to sleep is so that we can learn?
It sounds compelling, but of course the real world of research is much messier. Some findings appear to complicate, if not fully contradict, the idea of offline processing. For example, brain-damaged individuals who lack the ability to sleep in the slow-wave phase nonetheless have normal, even improved, memory. So do individuals whose REM sleep is suppressed by antidepressant medications. Exactly how to reconcile these data with the previous findings is a subject of intense scientific debate. Newer findings in mice suggest that the brain uses the time to clean house, sweeping away the toxic molecules that are a byproduct of the brain doing its thinking. With more time and more research, we’ll gain a greater understanding of what the brain is doing as we sleep—and why.
For now, a consistent concept emerges: Sleep is intimately involved in learning. It is observable with large amounts of sleep; it is observable with small amounts of sleep; it is observable all the time. It is time we did a better job of observing its importance in our lives.
More ideas
If businesses and schools took sleep seriously, what would a modern office building look like? A modern school? These are not idle questions. The effects of sleep deprivation are thought to cost US businesses more than $100 billion a year.
Match schedules to chronotypes
Behavioral tests can easily discriminate larks from owls from hummingbirds. Given advances in genetic research, in the future you may need only a blood test to characterize your process C and process S graphs. That means you can determine the hours when you are likely to experience productivity peaks. Twenty percent of the workforce is already at suboptimal productivity in the current nine-to-five model. So here’s an obvious idea: Set your schedule—whether college class schedule or work schedule—to match your chronotype.
Businesses could create several work schedules, based on the chronotypes of the employees. They might gain more productivity and a greater quality of life for those unfortunate people who otherwise are doomed to carry a permanent sleep debt. A business of the future takes sleep schedules seriously.
We could do the same in education. Teachers are just as likely to be late chronotypes as their students. Why not put them together? You might increase the competencies of both the teacher and the students. Freed of the nagging consequences of their sleep debts, each might be more fully capable of mobilizing his or her God-given IQ.
Variable schedules also would take advantage of the fact that sleep needs change throughout a person’s life. For example, data suggest that students temporarily shift to more of an owl chronotype as they transit through their teenage years. This has led some school districts to start their high-school classes after 9:00 a.m. This may make some sense. Sleep hormones (such as the protein melatonin) are at their maximum levels in the teenage brain. The natural tendency of these kids is to sleep more, especially in the morning. As we age, we tend to get less sleep, and some evidence suggests we need less sleep, too. An employee who starts out with her greatest productivity in one schedule may, as the years go by, keep a similar high level of output simply by switching to a different schedule.
Respect the nap zone
Don’t schedule meetings or classes during the time when the process C and process S curves are flatlined. Don’t give high-demand presentations or take critical exams anywhere near the collision of these two curves. Can you actually get a nap? That’s often easier said than done. College students can perhaps get back to their dorm rooms. Stay-at-home parents might be able to sleep when baby does. Some employees sneak out to their cars.
Even better would be if schools and businesses deliberately planned downshifts during the nap zone. Naps would be accorded the same deference that businesses reluctantly treat lunch, or even potty breaks: a necessary nod to an employee’s biological needs. Companies could create a designated space for employees to take one half-hour nap each workday. The advantage would be straightforward. People hired for their intellectual strength would be allowed to keep that strength in tip-top shape. “What other management strategy will improve people’s performance 34 percent in just 26 minutes?” said Mark Rosekind, the NASA scientist who conducted that eye-opening research on naps and pilot performance.
Sleep on it
Given the data about a good night’s rest, organizations might tackle their most intractable problems by having the entire “solving team” go on a mini-retreat. Once arrived, employees would be presented with the problem and asked to think about solutions. But they would not start coming to conclusions, or even begin sharing ideas with each other, before they had slept about eight hours. When they awoke, would the same increase in problem-solving rates available in the lab also be available to that team? It’s worth finding out.
Brain Rule #3
Sleep well, think well.
• The brain is in a constant state of tension between cells and chemicals that try to put you to sleep and cells and chemicals that try to keep you awake.
• The neurons of your brain show vigorous rhythmical activity when you’re asleep—perhaps replaying what you learned that day.
• People vary in how much sleep they need and when they prefer to get it, but the biological drive for an afternoon nap is universal.
• Loss of sleep hurts attention, executive function, working memory, mood, quantitative skills, logical reasoning, and even motor dexterity.
