Read an Excerpt
A Tour of Sleep
Considering that people on average will spend 25 years of their lives asleep, it's surprising how little most of us know about what goes on when the lights go off. It's almost as if our waking selves and sleeping selves are two separate beings living in alternate dimensions, never catching more than a passing glimpse of each other.
Most people don't seem very curious or concerned about this odd desire they have to close their eyes, lie down, and blank out for several hours every night...until something goes wrong, or even very, very wrong. Maybe it's that they can't fall asleep, or can't wake up, or find chocolate syrup and raw noodles in their hair in the morning, or have just pummeled their spouse with jackhammer legs, and wonder what in the world happened when they thought they were in bed and supposedly asleep.
Poets and philosophers have painted contradictory images of sleep, but its resemblance to death is often a theme. Edgar Allan Poe called sleep "those little slices of death," John Fletcher named sleep "Brother to Death," and Roman poet Ovid wrote, "What else is sleep but chill death's likeness?" But maybe it's William Shakespeare, who often wrote about insomnia, who captured it best when he called sleep "nature's soft nurse."
While it may look like nothing much is happening while a person is sleeping, there's actually a complicated chain of events going on in the brain, and that chain is vital to our overall health. With all the possibilities for the complicated chain of events to break down or even go haywire, it's surprising that sleep clinics aren't exploding with more people reporting all sorts of sleep problems.
We know that at least 10 percent of the U.S. population has a clinically significant sleep disorder, but it's hard for us to know just how many people have parasomnias—because it's still such a new field of study. Most medical schools continue to allocate little time in their curricula for teaching about sleep and its disorders, so if someone goes to a family doctor with a sleep-related complaint that's out of the ordinary, it's unlikely to be diagnosed and treated properly. And worse, plenty of people don't realize that they have "real" disorders; they assume that their strange sleep behaviors are just their own weird quirks that they have to live with. Many of my own patients had no idea anyone else had ever gone through what they'd gone through until they saw a magazine article or television report where a patient from our clinic described the same problems.
There's also reluctance among many to talk about their concerns because of the potential stigma involved. Until recently, even the medical community believed that people who exhibited violent or aggressive or sexual behavior in their sleep probably had unaddressed psychological problems. Surely that man who throws punches and shouts obscenities in his sleep really has some pent-up rage he's not addressing during the day, right? As it turns out, probably not. There are rare cases of parasomnias that are caused by purely psychological issues, but we've now discovered that the vast majority of those with extreme sleep disorders have psychological profiles that look no different from the rest of the population. Their brain chemistry and behavior have gone amok during sleep.
To understand what makes things go so wrong during sleep, though, first we need to know what normal sleep looks like. So let's take a tour.
The Stages of Sleep
There are two basic types of sleep: non-rapid eye movement (NREM) and rapid eye movement (REM). NREM sleep has four stages, and REM sleep is one stage, so together, they comprise five important stages of sleep that cycle throughout the night.
Stage 1 (NREM)
This is the hazy stage when you're just falling asleep. It's a very light sleep, and It's easily disrupted—if someone turns on a light or makes a noise, you'll probably awaken. Often, if you're awakened from your first stage 1 sleep, you don't even know you were asleep. Or you may remember the experience as an interruption or a disjointed train of thought or image. Your alpha rhythm (the predominant rhythm—8 to 12 cycles per second—seen with eyes closed during relaxed wakefulness) is reduced to less than 50 percent of total brain-wave activity, your muscle tone becomes relaxed, your eyes slowly roll back and forth, and you may experience sudden muscle contractions (hypnic jerks) that jolt you awake, sometimes with the sensation that you were falling. We aren't sure yet why these contractions happen, but it's nothing to worry about. Some people, however, move rapidly or even race through stage 1 sleep and virtually jump into stages 2, 3, and 4 sleep.
Your brain activity, though mixed, is dominated by theta waves, which run at 4 to 7 cycles per second. This stage usually lasts less than 10 minutes, but can last 30 minutes or even two hours in people with sleep-onset difficulties.
To successfully enter sleep, a person must be able to disengage from wakefulness while being able to engage in sleep, a necessary two-step, mind-brain-body process with inherent vulnerabilities.
Stage 2 (NREM)
This stage is generally considered the "baseline" of sleep—the clear-cut starting point. It's difficult to pinpoint to exact second someone falls asleep because it doesn't happen all at once, and a person may report being awake when the tests appear to show stage 1 sleep, or alternating between wakefulness and stage 1 sleep.
In stage 2, you're still in a moderately light sleep, and still fairly easy to arouse, but your heart rate slows down and your temperature drops in preparation for the deeper sleep to come. Your brain activity, which can be measured by scalp electrodes in a sleep lab, will show slower waves mixed with sporadic bursts of faster waves called sleep spindlesand also a brain wave pattern known as K-complexes that look like the letter "K". Sleep spindles and K-complexes are hallmarks of stage 2 sleep. As an adult, you'll spend about half of your total sleep time in stage 2.
Stage 3 (NREM)
Now you transition down to slow-wave sleep or delta sleep. Between 20 and 50 percent of this stage is made up of high-voltage, slow-wave activity known as delta waves, which run at 1 to 3 cycles per second. Stages 3 and 4 are often grouped together because there's not much that distinguishes them from a physiological standpoint.
Stage 4 (NREM)
It's a common misconception that REM sleep is the deepest sleep. Actually, stage 4 NREM is the deepest sleep, closely followed by stage 3. When you've been sleep deprived, your body craves delta sleep and will try to make up for lost time by getting you to stage 4 faster and keeping you there longer. When people say that someone is "out like a light" or in a "dead sleep," the person is probably in stage 3 or 4, when it's very difficult to arouse someone. This is the stage from which sleep terrors and sleepwalking are most likely to occur. Stage 4 is also the stage, it's thought, when the body does most of its repair work.
We name this stage after the most easily seen physical marker: rapid eye movements. When a person is in the REM stage, he or she will often show bursts of eye flutters and back-and-forth movements, possibly in conjunction with dreams. This is the stage when the most vivid and prolonged dreaming occurs. Your brain is highly active (on sleep graphs, it looks almost the same as your brain activity when you're awake), but your body is temporarily paralyzed by an active, generalized inhibition originating in the lower brain. Your muscles—even the ancillary respiratory muscles other than the diaphragm—are "shut down" and completely inert, and it's believed that this is to protect us from acting out our dreams. Your heart rate picks up; blood flow to the brain increases; respiration becomes erratic, faster, and shallower, with increased oxygen consumption; metabolism increases; sexual arousal occurs, with men developing erections and women clitoral engorgement; and blood pressure rises. Your brain activity shows low-voltage, fast-frequency waves. You also lose some of your ability to regulate your body temperature during this stage, so you're more susceptible to the temperature of your surroundings.
REM sleep is thought to be especially important in learning and memory processing, but there is much debate still about what exactly takes place. The ease of arousing someone from REM sleep varies, but it's usually far easier to wake someone from REM sleep than from stage 3 or 4 sleep. You can also become alert much more quickly when someone wakes you out of REM sleep than when you are aroused out of delta NREM sleep. About 20 to 25 percent of an adult's total sleep time in spent in the REM stage.
You might think that the sleep cycle would progress as stages 1, 2, 3, and 4, then REM, then repeat, but it often doesn't occur in quite such a regular manner. Instead, a typical adult sleep cycle looks more like the following.
Stage 1 for up to 10 minutes, stage 2 for 10 to 15 minutes, stage 3 for about 5 minutes, stage 4 for 20 to 40 minutes, then back to stage 3 for just a minute or two, stage 2 for 5 to 10 minutes, then REM for up to 5 minutes.
The first REM stage begins about 90 minutes into sleep, then the cycle starts again about every 90 minutes throughout the night.
During the earlier cycles, stages 3 and 4 are at their longest, but they get shorter and may drop out altogether in later cycles, with stage 2 lengthening to fill in the gap. The REM stage gets longer in the later cycles. In total, you'll spend about 75 to 80 percent of the night in NREM sleep and 20 to 25 percent in REM sleep.
The progression of sleep cycling appears to satisfy metabolic needs in the first part of the cycle (with increased amounts of delta NREM sleep) and brain activation in the second part of the cycle (with increased amounts of REM sleep).
It's normal to have brief awakenings during the night, particularly during the later cycles, around the transitions to and from REM sleep. With any luck, you won't even remember these awakenings, because they may last only a few seconds.
In addition to the importance of proper sleep cycling once we are asleep, there are other rhythms that play a key role in the timing of our sleep—the circadian rhythms.
The earth completes a rotation on its axis once every 24 hours, and as humans, we are built to respond to that rotation, scheduling our daily needs and tasks at appropriate times according to our environment, so that we are awake when there is sunlight and we are asleep after the sun has set and there is darkness. Circadian gets its meaning from the Latin roots circa, meaning "about," and dies, meaning "day." So a circadian rhythm is the cycle of "about a day." It's governed by your suprachiasmatic nucleus (SCN), which resides in the hypothalamus region of the brain, situated in the area between and just behind the eyes. Commonly referred to as an internal or biological clock, the SCN rules your body's natural programming, and it's adapted (entrained) to the approximate 24-hour day-night cycle.
The SCN picks up cues from the retina at the back of our eyes to determine when it's daytime and when it's night, judging by the amount of daylight or darkness. The SCN then passes messages around to other parts of the brain and body to direct the appropriate schedule for producing hormones, eating, and sleeping, and other vital functions. It determines when the hormone melatonin should be released from the pineal gland in the center of the brain—turned on at night and shut down during the day—to help us sleep at appropriate times.
People become keenly aware of their circadian rhythms when they attempt to change their sleeping patterns rapidly. For example, if you've taken a trip to a different time zone, you've undoubtedly experienced jet lag. This is because resetting the internal clock isn't a fast process. It can take several days (or even weeks) for the body to get adjusted to the new cues for day and night, and during that time, you'll probably feel sleepy and "foggy," and maybe irritable. Night-shift workers, or those whose work shifts change from week to week or from day to day, can also butt heads with their internal clocks.
The body doesn't want us to just pick any eight hours for sleep; it wants us to sleep in tune with the proper cues. We're made to feel alert when the daylight hits and to get sleepy when it's dark outside. Although you can psychologically get used to a schedule that falls outside of these parameters, you'll still be fighting your biological clock and be at risk for various health problems, which over the long run could include being at increased risk for depression, heart disease, and metabolic disorders.
We don't yet fully understand the interplay of external cues (light and dark) and our internal clock that creates the circadian pattern. Interestingly, without any external cues our internal circadian rhythm, driven by the SCN, falls out of sync with the normal 24-hour sun cycle, and on average becomes 24.2 hours.
AGE-RELATED CHANGES IN SLEEP
As you age, your sleep patterns age too.
Newborns typically enter sleep the opposite way adults do; they go straight to REM sleep, known as active sleep in newborns. And their cycles are shorter than adult cycles: 50 to 60 minutes on average.
Starting around age one, babies shift to entering sleep through NREM stage 1, as they'll do for the rest of their lives. Young children have longer durations of slow-wave sleep (stages 3 and 4) than do adults, and it's even harder to arouse a young child from these stages of sleep as compared to an adult. Children are known to be prone to sleepwalking, and studies show that up to 17 percent of children sleepwalk, with the behavior peaking at age 11 or 12—but people rarely recognize how often sleepwalking continues into, or begins to occur, in adulthood. (4 percent of adults sleepwalk).
Adolescent and Young-Adult Years
As children reach preteen and teenage years, their sleep recipes will change drastically; they will lose about 40 percent of their slow-wave sleep despite needing about the same amount of total sleep.
They also seem to be programmed in major conflict with most school schedules. During puberty, biological changes shift an adolescent's internal "clock," making it more natural for a preteen or teen to fall asleep around 11:00 p.m. to midnight. They still need about nine hours of sleep per night, the same as they did during their grade school years. However, because the school day may begin at 7:00 a.m. (or earlier, for those with before-school activities!), many adolescents don't get enough sleep, which results in daytime sleepiness and a tendency to fall asleep during class.
It can be very difficult for adolescents to fight their internal programming to stay alert at time when they feel like sleeping, or go to bed early at times when they feel wide awake. Building up a big sleep debt (from prolonged periods if sleep deprivation) can interfere with a person's ability to concentrate and learn, make the person feel more irritable, and have other adverse effects on health. The effects of chronic sleep deprivation can also be mistaken for attention deficit hyperactivity disorder (ADHD). Because of this, there have been efforts in some school districts to adopt later start times.
One of the more troubling effects of sleep deprivation is falling asleep behind the wheel: In a North Carolina study, more than half of all fall-asleep crashes involved people 25 years of age or younger.
In August 2006 the impact of sleep deprivation again made tragic headlines when a Comair jet crashed in a Kentucky field because it took off from the wrong runway, killing 49 people. It was revealed that the sole air traffic controller on duty had slept for just two hours before his overnight shift. He had nine hours off in between work shifts, having worked all morning and part of the afternoon on Saturday, then returned Saturday night to work through Sunday morning. Investigators are studying his schedule to estimate how much of a role sleepiness may have played in this accident.
Early to Mid-Adulthood
During the early years, slow-wave sleep hasn't dropped much below its adolescent level, REM sleep remains constant, and you typically need less sleep than you did in earlier years.
The National Sleep Foundation polled adults between the ages of 18 and 54 and found that those in this age group often play a game of "catch-up," where they don't get enough sleep on weeknights (6.7 hours per night, on average), then try to compensate by sleeping more on weekend nights (7.6 hours per night, on average). Work and school schedules clearly play a part in this pattern. About 16 percent of adults usually sleep less than 6 hours per night.
Different people have different sleep needs: Seven hours may be enough for one person to feel rested, whereas another may need more than nine hours to be at his best. Although most adults have heard that the magic number is eight hours, that's not true for everyone. Not all people who naturally sleep less than that are sleep deprived, and not all people who sleep more than that are lazy! Likewise, it appears that the tendency to be a "morning person" or a "night person" is something we're born with. We all have unique biological needs and do our best when we accept them instead of forcing ourselves to fight them. The important questions are how do we feel and how do we function during the daytime after getting a certain amount of sleep during most nights—if we feel good, then we are getting enough sleep, but if the sleep we're getting makes us feel tired, then either we need to get more sleep or else we have a sleep problem that needs to be addressed.
Studies have shown that up to half of women have sleep disturbances around the time they enter menopause. One stuffy of menopausal women classified 42.1 percent of them as "poor sleepers," with depression and aging showing significant effects on quality sleep.
Elderly people have the most sleep difficulty of all, though, reporting high levels of insomnia, restless legs syndrome, sleep-related breathing disorders, and intrusive early-morning awakenings. Many factors can contribute to this, such as other health problems (painful conditions may keep a person awake) and medications. There's nothing about the aging process itself that should cause sleep problems.
In 2003, the national Sleep Foundation conducted a large-scale poll of Americans between the ages of 55 and 84 to learn more about their sleep behaviors in relation to their overall health, activities, moods, and outlooks on life. They surveyed 1,506 people by the phone and discovered something that should seem obvious but is rarely discussed: The better the person's overall health, the better his or her sleep. And vice versa: The higher the number of medical conditions, the more likely it is for the person to report sleep problems. This type of correlation also held true with lifestyle and outlooks: Those with more active lifestyles and a more positive outlook on life tended to have fewer sleep complaints.
On average, older people sleep 7 hours on weeknights and 7.1 hours on weekend nights, according to this poll. Sixty-seven percent report having sleep problems at least a few times a week, including difficulty falling asleep, frequent awakenings throughout the nights, inability to go back to sleep after an unwanted awakening, pauses in breathing, and unpleasant feelings in their legs. Older women were more likely to snore and have sleep-related breathing problems.
Only about 8 percent of respondents had actually been diagnosed with a sleep disorder, however.
WHY IS SLEEP IMPORTANT?
At a time when the Internet, Starbucks, and late-night television have turned us into a nation of the sleep-deprived and hyperalert, the concept of a "good night's sleep" seems elusive, maybe even a little old-fashioned. But the truth is that researchers have crossed a threshold into a new understanding of the importance of sleep.
The question of why we sleep isn't as easy to answer as you might expect. Aristotle decided in 350 B.C. that it must have something to do with digestion. In his treatise On Sleep and Sleeplessness, translated by J.I. Beare, Aristotle explained that when food is digested, it releases hot vapors into the veins, which turn into blood and wind up in the heart. This makes a person feel heavy and lie down. The outer body parts get cool, which makes the eyelids droop. Then sleep occurs "until the purest part of this blood has been separated off into the upper parts of the body, and the most turbid into the lower parts...Also, as a general rule, persons whose veins are inconspicuous, as well as those who are dwarf-like, or have abnormally large heads, are addicted to sleep," he explained.
Later, physicians decided that sleep must be the result of too much blood getting congested in the brain. Or maybe the opposite—too much blood had fallen out of the brain, making the brain shut down and the body lie horizontally to encourage the blood to get back in there.
Well, we've come a long way in our understanding of how sleep works, but we're still not sure exactly why it happens. Many experts believe it's to "recharge" our energy supplies and repair our bodies, much like charging up a cell phone after using it all day. Certain hormones, such as growth hormone, are released during sleep, and the body tissues go through repair processes.
Others think sleep's primary function is to process our memories, store them appropriately, and promote learning. It may be that sleep helps us to file away what we learned that day, and get rid of non-useful memories that are taking up room in the brain. Various other theories exist about the function of sleep, such as 'sleep is of the brain and for the brain"—this is, optimizing brain function is the main purpose of sleep.
The best way to illustrate why we need sleep is to examine what happens when we don't get enough sleep during many or most nights—or when our sleep quality is poor:
- Concentration decreases.
- Decision-making ability declines.
- Irritability and frustration increase.
- Motor function is impaired.
- Speech is impaired.
- Car accidents are more common.
- Workplace accidents are more common.
- Ability to fight illness and disease declines.
- Mental and physical health disorders worsen.
- The aging process may be speeded up.
Sometimes the consequences of sleep deprivation are minor (like nodding off while watching a movie), but long-term sleep deprivation can have serious consequences like hallucinations and even suicidal thinking. Sometimes sleep deprivation can be catastrophic. Major disasters such as the nuclear power plant accident at Three Mile Island, the Exxon Valdez oil spill, the 1984 gas leak in Bhopal, and the disaster of the space shuttle Challenger were all officially attributed to sleepiness-related impaired judgment in the workplace. Major problems and disasters are much less likely to occur, and can be handled much more efficiently, when good sleepers are in charge.
Recent research from the Walter Reed Army Institute of research has shown that soldiers who are substantially sleep deprived have diminished decision-making capabilities, constructive thinking, and "moral reasoning." Soldiers who were forced to stay awake for 53.5 hours tended to judge controversial solutions to moral dilemmas on a test as "acceptable" more often than they would when they were rested. In other words, there is diminished critical thinking in the sleep-deprived state.
So even id scientists can't agree on exactly why we sleep, we can all agree that it cycles through five predictable stages; it changes as we age; and it is essential for virtually all creatures, clearly serving multiple beneficial purposes. As we'll explore further in later chapters, we also know that parasomnias can emerge in males and females from any sleep stage at any time of life—even in utero.
Sleep in the City: Where does your city rank?
- Best Cities for Sleep:
- Minneapolis, MN
- Anaheim, CA
- San Diego, CA
- Raleigh-Durham, NC
- Washington, DC
- Worst Cities for Sleep:
- Detroit, MI
- Cleveland, OH
- Nashville, TN
- Cincinnati, OH
- New Orleans, LA