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
