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
