3-4 What is sleep?

Sleep—the irresistible tempter to whom we inevitably succumb. Sleep—the equalizer of presidents and peasants. Sleep—sweet, renewing, mysterious sleep. While sleeping, you may feel “dead to the world,” but you are not. Even when you are deeply asleep, your perceptual window is open a crack. You move around on your bed, but you manage not to fall out. The occasional roar of passing vehicles may leave your deep sleep undisturbed, but a baby’s cry interrupts it. So does the sound of your name. EEG recordings confirm that the brain’s auditory cortex responds to sound stimuli even during sleep (Kutas, 1990). And when you sleep, as when awake, you process most information outside your conscious awareness.

Many of sleep’s mysteries are being solved as some people sleep, attached to recording devices, while others observe. By recording brain waves and muscle movements, and by observing and occasionally waking sleepers, researchers are glimpsing things that a thousand years of common sense never told us. Perhaps you can anticipate some of their discoveries. Are the following statements true or false?

All these statements (adapted from Palladino & Carducci, 1983) are false. To see why, read on.

Like the ocean, life has its rhythmic tides. Over varying time periods, our bodies fluctuate, and with them, our minds. Let’s look more closely at two of those biological rhythms—our 24-hour biological clock and our 90-minute sleep cycle.

3-5 How do our biological rhythms influence our daily functioning?

The rhythm of the day parallels the rhythm of life—from our waking at a new day’s birth to our nightly return to what Shakespeare called “death’s counterfeit.” Our bodies roughly synchronize with the 24-hour cycle of day and night thanks to an internal biological clock called the circadian rhythm (from the Latin circa, “about,” and diem, “day”). As morning approaches, body temperature rises, then peaks during the day, dips for a time in early afternoon (when many people take siestas), and begins to drop again in the evening. Thinking is sharpest and memory most accurate when we are at our daily peak in circadian arousal. Try pulling an all-nighter or working an occasional night shift. You’ll feel groggiest in the middle of the night but may gain new energy when your normal wake-up time arrives.

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Age and experience can alter our circadian rhythm. Most 20-year-olds are evening-energized “owls,” with performance improving across the day (May & Hasher, 1998). Most older adults are morning-loving “larks,” with performance declining as the day wears on. By mid-evening, when the night has hardly begun for many young adults, retirement homes are typically quiet. After about age 20 (slightly earlier for women), we begin to shift from being owls to being larks (Roenneberg et al., 2004). Women become more morning oriented as they have children and also as they transition to menopause (Leonhard & Randler, 2009; Randler & Bausback, 2010). Night owls tend to be smart and creative (Giampietro & Cavallera, 2007). Morning types tend to do better in school, to take more initiative, and to be less vulnerable to depression (Randler, 2008, 2009; Preckel et al., 2013).

3-6 What is the biological rhythm of our sleeping and dreaming stages?

Sooner or later, sleep overtakes us and consciousness fades as different parts of our brain’s cortex stop communicating (Massimini et al., 2005). Yet the sleeping brain remains active and has its own biological rhythm.

About every 90 minutes, we cycle through four distinct sleep stages. This simple fact apparently was unknown until 8-year-old Armond Aserinsky went to bed one night in 1952. His father, Eugene, a University of Chicago graduate student, needed to test an electroencephalograph he had repaired that day (Aserinsky, 1988; Seligman & Yellen, 1987). Placing electrodes near Armond’s eyes to record the rolling eye movements then believed to occur during sleep, Aserinsky watched the machine go wild, tracing deep zigzags on the graph paper. Could the machine still be broken? As the night proceeded and the activity recurred, Aserinsky realized that the periods of fast, jerky eye movements were accompanied by energetic brain activity. Awakened during one such episode, Armond reported having a dream. Aserinsky had discovered what we now know as REM sleep (rapid eye movement sleep).

Similar procedures used with thousands of volunteers showed the cycles were a normal part of sleep (Kleitman, 1960). To appreciate these studies, imagine yourself as a participant. As the hour grows late, you feel sleepy and yawn in response to reduced brain metabolism. (Yawning, which can be socially contagious, stretches your neck muscles and increases your heart rate, which increases your alertness [Moorcroft, 2003].) When you are ready for bed, a researcher comes in and tapes electrodes to your scalp (to detect your brain waves), on your chin (to detect muscle tension), and just outside the corners of your eyes (to detect eye movement; FIGURE 3.10). Other devices will record your heart rate, respiration rate, and genital arousal.

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When you are in bed with your eyes closed, the researcher in the next room sees on the EEG the relatively slow alpha waves of your awake but relaxed state (FIGURE 3.11). As you adapt to all this equipment, you grow tired and, in an unremembered moment, slip into sleep (FIGURE 3.12). The transition is marked by the slowed breathing and the irregular brain waves of non-REM stage 1 sleep. Using the American Academy of Sleep Medicine classification of sleep stages, this is called NREM-1 (Silber et al., 2008).

In one of his 15,000 research participants, William Dement (1999) observed the moment the brain’s perceptual window to the outside world slammed shut. Dement asked a sleep-deprived young man with eyelids taped open to press a button every time a strobe light flashed in his eyes (about every 6 seconds). After a few minutes the young man missed one. Asked why, he said, “Because there was no flash.” But there was a flash. He missed it because (as his brain activity revealed) he had fallen asleep for 2 seconds, missing not only the flash 6 inches from his nose but also the awareness of the abrupt moment of entry into sleep.

During this brief NREM-1 sleep you may experience fantastic images resembling hallucinations—sensory experiences that occur without a sensory stimulus. You may have a sensation of falling (at which moment your body may suddenly jerk) or of floating weightlessly. These hypnagogic sensations may later be incorporated into your memories. People who claim to have been abducted by aliens—often shortly after getting into bed—commonly recall being floated off of or pinned down on their beds (Clancy, 2005; McNally, 2012).

You then relax more deeply and begin about 20 minutes of NREM-2 sleep, with its periodic sleep spindles—bursts of rapid, rhythmic brain-wave activity. Although you could still be awakened without too much difficulty, you are now clearly asleep.

Then you transition to the deep sleep of NREM-3. During this slow-wave sleep, which lasts for about 30 minutes, your brain emits large, slow delta waves and you are hard to awaken. (It is at the end of the deep, slow-wave NREM-3 sleep that children may wet the bed.)

About an hour after you first fall asleep, a strange thing happens. Rather than continuing in deep slumber, you ascend from your initial sleep dive. Returning through NREM-2 (where you spend about half your night), you enter the most intriguing sleep phase—REM sleep (FIGURE 3.13). For about 10 minutes, your brain waves become rapid and saw-toothed, more like those of the nearly awake NREM-1 sleep. But unlike NREM-1, during REM sleep your heart rate rises, your breathing becomes rapid and irregular, and every half-minute or so your closed eyes dart around in momentary bursts of activity. These eye movements announce the beginning of a dream—often emotional, usually story-like, and richly hallucinatory. Because anyone watching a sleeper’s eyes can notice these REM bursts, it is amazing that science was ignorant of REM sleep until 1952.

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Except during very scary dreams, your genitals become aroused during REM sleep. You have an erection or increased vaginal lubrication and clitoral engorgement, regardless of whether the dream’s content is sexual (Karacan et al., 1966). Men’s common “morning erection” stems from the night’s last REM period, often just before waking. In young men, sleep-related erections outlast REM periods, lasting 30 to 45 minutes on average (Karacan et al., 1983; Schiavi & Schreiner-Engel, 1988). A typical 25-year-old man therefore has an erection during nearly half his night’s sleep, a 65-year-old man for one-quarter. Many men troubled by erectile disorder (impotence) have sleep-related erections, suggesting the problem is not between their legs.

Your brain’s motor cortex is active during REM sleep, but your brainstem blocks its messages. This leaves your muscles relaxed, so much so that, except for an occasional finger, toe, or facial twitch, you are essentially paralyzed. Moreover, you cannot easily be awakened. (This immobility may occasionally linger as you awaken from REM sleep, producing a disturbing experience of sleep paralysis [Santomauro & French, 2009].) REM sleep is thus sometimes called paradoxical sleep: The body is internally aroused, with waking-like brain activity, yet asleep and externally calm.

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The sleep cycle repeats itself about every 90 minutes for younger adults (somewhat more frequently for older adults). As the night wears on, deep NREM-3 sleep grows shorter and disappears. The REM and NREM-2 sleep periods get longer (see Figure 3.13). By morning, we have spent 20 to 25 percent of an average night’s sleep—some 100 minutes—in REM sleep. Thirty-seven percent of people report rarely or never having dreams “that you can remember the next morning” (Moore, 2004). Yet even they will, more than 80 percent of the time, recall a dream after being awakened during REM sleep. We spend about 600 hours a year experiencing some 1500 dreams, or more than 100,000 dreams over a typical lifetime—dreams swallowed by the night but not acted out, thanks to REM’s protective paralysis.

3-7 How do biology and environment interact in our sleep patterns?

The idea that “everyone needs 8 hours of sleep” is untrue. Newborns often sleep two-thirds of their day, most adults no more than one-third (with some thriving on fewer than 6 hours nightly, others racking up 9 or more). There is more to our sleep differences than age. Some are awake between nighttime “first sleep” and “second sleep” periods (Randall, 2012). And some find that a 15-minute midday nap equals another hour of nighttime sleep (Horne, 2011).

Sleep patterns are genetically influenced (Hor & Tafti, 2009). In studies of fraternal and identical twins, only the identical twins had strikingly similar sleep patterns and durations (Webb & Campbell, 1983). Researchers are discovering the genes that regulate sleep in humans and animals (Donlea et al., 2009; He et al., 2009). Sleep patterns are also culturally influenced. In the United States and Canada, adults average 7 to 8 hours per night (Hurst, 2008; National Sleep Foundation [NSF], 2010; Robinson & Martin, 2009). The weeknight sleep of many students and workers falls short of this average, however (NSF, 2008). And thanks to modern lighting, shift work, and social media diversions, many who would have gone to bed at 9:00 p.m. a century ago are now up until 11:00 p.m. or later. With sleep, as with waking behavior, biology and environment interact.

Bright morning light tweaks the circadian clock by activating light-sensitive retinal proteins. These proteins control the circadian clock by triggering signals to the brain’s suprachiasmatic nucleus (SCN)—a pair of grain-of-rice-sized, 10,000-cell clusters in the hypothalamus (Wirz-Justice, 2009). The SCN does its job partly by causing the brain’s pineal gland to decrease its production of the sleep-inducing hormone melatonin in the morning and to increase it in the evening (FIGURE 3.14).

Being bathed in (or deprived of) light disrupts our 24-hour biological clock (Czeisler et al., 1999; Dement, 1999). Curiously—given that our ancestors’ body clocks were attuned to the rising and setting Sun of the 24-hour day—many of today’s young adults adopt something closer to a 25-hour day, by staying up too late to get 8 hours of sleep. For this, we can thank (or blame) Thomas Edison, inventor of the light bulb. This helps explain why, until our later years, we must discipline ourselves to go to bed and force ourselves to get up. Most animals, too, when placed under unnatural constant illumination will exceed a 24-hour day. Artificial light delays sleep.

Sleep often eludes those who stay up late and sleep in on weekends, and then go to bed earlier on Sunday evening in preparation for the new workweek (Oren & Terman, 1998). Like New Yorkers whose biology is on California time, they experience “social jet lag.” For North Americans who fly to Europe and need to be up when their circadian rhythm cries “SLEEP,” bright light (spending the next day outdoors) helps reset the biological clock (Czeisler et al., 1986, 1989; Eastman et al., 1995).

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3-8 What are sleep’s functions?

So, our sleep patterns differ from person to person. But why do we have this need for sleep?

Psychologists believe sleep may exist for five reasons.

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A regular full night’s sleep can also “dramatically improve your athletic ability,” report James Maas and Rebecca Robbins (2010). Well-rested athletes have faster reaction times, more energy, and greater endurance, and teams that build 8 to 10 hours of daily sleep into their training show improved performance. One study observed Stanford University men’s basketball players’ performance for about three weeks. During an ensuing five to seven weeks of extended sleep—aiming for 10 hours in bed—their average sleep increased 110 minutes per night, their sprint times decreased, and their free throw and 3-point shooting percentages both increased 9 percent (Mah et al., 2011). Top violinists also report sleeping 8.5 hours a day on average, and rate practice and sleep as the two most important improvement-fostering activities (Ericsson et al., 1993).

Slow-wave sleep, which occurs mostly in the first half of a night’s sleep, produces the human growth hormone necessary for muscle development. REM sleep and NREM-2 sleep, which occur mostly in the final hours of a long night’s sleep, help strengthen the neural connections that build enduring memories, including the “muscle memories” learned while practicing tennis or shooting baskets.

The optimal exercise time is late afternoon or early evening, Maas and Robbins advise, when the body’s natural cooling is most efficient. Early morning workouts are ill-advised, because they increase the risk of injury and rob athletes of valuable sleep. Heavy workouts within three hours of bedtime should also be avoided because the arousal disrupts falling asleep. Precision muscle training, such as shooting free throws or piano playing, benefits when practiced shortly before sleep (Holz et al., 2012; Tamaki et al., 2013).

Maas has been a sleep consultant for college and professional athletes and teams. On his advice, basketball’s Orlando Magic cut early morning practices. He also advised one young woman, Sarah Hughes, who felt stymied in her efforts to excel in figure-skating competition. “Cut the early morning practice,” he instructed, as part of the recommended sleep regimen. Soon thereafter, Hughes’ performance scores increased, ultimately culminating in her 2002 Olympic gold medal. Given all the benefits of sleep, it’s no wonder that sleep loss hits us so hard.

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3-9 How does sleep loss affect us, and what are the major sleep disorders?

When our body yearns for sleep but does not get it, we begin to feel terrible. Trying to stay awake, we will eventually lose. In the tiredness battle, sleep always wins.

Today, more than ever, our sleep patterns leave us not only sleepy but drained of energy and feelings of well-being. After a succession of 5-hour nights, we accumulate a sleep debt that need not be entirely repaid but cannot be satisfied by one long sleep. “The brain keeps an accurate count of sleep debt for at least two weeks,” reported sleep researcher William Dement (1999, p. 64).

Obviously, then, we need sleep. Sleep commands roughly one-third of our lives—some 25 years, on average. Allowed to sleep unhindered, most adults will sleep at least 9 hours a night (Coren, 1996). With that much sleep, we awake refreshed, sustain better moods, and perform more efficient and accurate work. The U.S. Navy and the National Institutes of Health have demonstrated the benefits of unrestricted sleep in experiments in which volunteers spent 14 hours daily in bed for at least a week. For the first few days, the volunteers averaged 12 hours of sleep a day or more, apparently paying off a sleep debt that averaged 25 to 30 hours. That accomplished, they then settled back to 7.5 to 9 hours nightly and felt energized and happier (Dement, 1999). In one Gallup survey (Mason, 2005), 63 percent of adults who reported getting the sleep they needed also reported being “very satisfied” with their personal life (as did only 36 percent of those needing more sleep). And when 909 working women reported on their daily moods, the researchers were struck by what mattered little (such as money, so long as the person was not battling poverty), and what mattered a lot: less time pressure at work and a good night’s sleep (Kahneman et al., 2004).

College and university students are especially sleep deprived; 69 percent in one national survey reported “feeling tired” or “having little energy” on several or more days in the last two weeks (AP, 2009). For students, less sleep also predicts more conflicts in friendships and romantic relationships (Gordon & Chen, 2014; Tavernier & Willoughby, 2014). Tired triggers crabby. In another survey, 28 percent of high school students acknowledged falling asleep in class at least once a week (National Sleep Foundation, 2006). The going needn’t get boring before students start snoring.

Sleep loss is also a predictor of depression. Researchers who studied 15,500 12- to 18-year-olds found that those who slept 5 or fewer hours a night had a 71 percent higher risk of depression than their peers who slept 8 hours or more (Gangwisch et al., 2010). This link does not appear to reflect an effect of depression on sleep. When children and youth are followed through time, sleep loss predicts depression rather than vice versa (Gregory et al., 2009). Moreover, REM sleep’s processing of emotional experiences helps protect against depression (Walker & van der Helm, 2009). After a good night’s sleep, we often do feel better the next day. And that may help to explain why parentally enforced bedtimes predict less depression, and why pushing back school start times leads to improved adolescent sleep, alertness, and mood (Gregory et al., 2009; Owens et al., 2010; Perkinson-Gloor et al., 2013).

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Sleep-deprived students often function below their peak. And they know it: Four in five teens and three in five 18- to 29-year-olds wish they could get more sleep on weekdays (Mason, 2003, 2005). Yet that teen who staggers glumly out of bed in response to an unwelcome alarm, yawns through morning classes, and feels half-depressed much of the day may be energized at 11:00 p.m. and mindless of the next day’s looming sleepiness (Carskadon, 2002). “Sleep deprivation has consequences—difficulty studying, diminished productivity, tendency to make mistakes, irritability, fatigue,” noted Dement (1999, p. 231). A large sleep debt “makes you stupid.”

It can also make you gain weight. Sleep deprivation

Thus, children and adults who sleep less are fatter than average, and in recent decades people have been sleeping less and weighing more (Shiromani et al., 2012). Moreover, experimental sleep deprivation of adults increases appetite and eating (Nixon et al., 2008; Patel et al., 2006; Spiegel et al., 2004; Van Cauter et al., 2007). So, sleep loss helps explain the common weight gain among sleep-deprived students (Hull et al., 2007).

Sleep also affects our physical health. When infections do set in, we typically sleep more, boosting our immune cells. Sleep deprivation can suppress immune cells that battle viral infections and cancer (Möller-Levet et al., 2013; Motivala & Irwin, 2007). One experiment exposed volunteers to a cold virus. Those who had been averaging less then 7 hours’ sleep a night were three times more likely to develop a cold than were those sleeping 8 or more hours a night (Cohen et al., 2009). Sleep’s protective effect may help explain why people who sleep 7 to 8 hours a night tend to outlive those who are chronically sleep deprived, and why older adults who have no difficulty falling or staying asleep tend to live longer than their sleep-deprived agemates (Dement, 1999; Dew et al., 2003).

Sleep deprivation slows reactions and increases errors on visual attention tasks similar to those involved in screening airport baggage, performing surgery, and reading X-rays (Caldwell, 2012; Lim & Dinges, 2010). Slow responses can also spell disaster for those operating equipment, piloting, or driving. Driver fatigue has contributed to an estimated 20 percent of American traffic accidents (Brody, 2002) and to some 30 percent of Australian highway deaths (Maas, 1999). One two-year study examined the driving accidents of more than 20,000 Virginia 16- to 18-year-olds in two major cities. In one city, the high schools started 75 to 80 minutes later than in the other. The late starters had about 25 percent fewer crashes (Vorona et al., 2011). When sleepy frontal lobes confront an unexpected situation, misfortune often results.

Stanley Coren capitalized on what is, for many North Americans, a semi-annual sleep-manipulation experiment—the “spring forward” to daylight saving time and “fall backward” to standard time. Searching millions of records, Coren found that in both Canada and the United States, accidents increased immediately after the time change that shortens sleep (FIGURE 3.16). Less sleep = more accidents.

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Tired people have trouble concentrating, which leads to more “cyberloafing”—frittering away time online. On the Monday after daylight saving time begins, entertainment-related Google searches have been 3.1 percent higher than on the preceding Monday, and 6.4 higher than on the following Monday (Wagner et al., 2012). Another study showed sleep-deprived students (compared to well-rested students) spending more time cyberloafing during a 42-minute video lecture.

FIGURE 3.17 summarizes the effects of sleep deprivation. But there is good news! Psychologists have discovered a treatment that strengthens memory, increases concentration, boosts mood, moderates hunger, reduces obesity, fortifies the disease-fighting immune system, and lessens the risk of fatal accidents. Even better news: The treatment feels good, it can be self-administered, the supplies are limitless, and it’s free! If you are a typical university-age student, often going to bed near 2:00 a.m. and dragged out of bed six hours later by the dreaded alarm, the treatment is simple: Each night just add 15 minutes to your sleep.

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No matter what their normal need for sleep, 1 in 10 adults, and 1 in 4 older adults, complain of insomnia—persistent problems in either falling or staying asleep (Irwin et al., 2006). The result is tiredness and increased risk of depression (Baglioni et al., 2011). All of us, when anxious or excited, may have trouble sleeping. (And smart phones under the pillow and used as alarm clocks increase the likelihood of disrupted sleep.) From middle age on, awakening occasionally during the night becomes the norm, not something to fret over or treat with medication (Vitiello, 2009). Ironically, insomnia is worsened by fretting about it. In laboratory studies, insomnia complainers do sleep less than others. But they typically overestimate how long it takes them to fall asleep and underestimate how long they actually have slept (Harvey & Tang, 2012). Even if we have been awake only an hour or two, we may think we have had very little sleep because it’s the waking part we remember.

The most common quick fixes for true insomnia—sleeping pills and alcohol—can aggravate the problem, reducing REM sleep and leaving the person with next-day blahs. Such aids can also lead to tolerance—a state in which increasing doses are needed to produce an effect. An ideal sleep aid would mimic the natural chemicals abundant during sleep, reliably producing sound sleep without side effects. Until scientists can supply this magic pill, sleep experts have offered some tips for getting better quality sleep (TABLE 3.1).

Falling asleep is not the problem for people with narcolepsy (from narco, “numbness,” and lepsy, “seizure”), who have sudden attacks of overwhelming sleepiness, usually lasting less than 5 minutes. Narcolepsy attacks can occur at the most inopportune times, perhaps just after taking a terrific swing at a softball or when laughing loudly, shouting angrily, or having sex (Dement, 1978, 1999). In severe cases, the person collapses directly into a brief period of REM sleep, with loss of muscular tension. People with narcolepsy—1 in 2000 of us, estimated the Stanford University Center for Narcolepsy (2002)—must therefore live with extra caution. As a traffic menace, “snoozing is second only to boozing,” says the American Sleep Disorders Association, and those with narcolepsy are especially at risk (Aldrich, 1989).

Researchers have discovered genes that cause narcolepsy in dogs and humans, such as by producing an immune system attack on brain cells that enable alertness (De la Herrán-Arita et al., 2013; Miyagawa et al., 2008). Genes help sculpt the brain, and neuroscientists are searching the brain for narcolepsy-linked abnormalities. One team discovered a relative absence of a hypothalamic neural center that produces orexin (also called hypocretin), an alertness-related neurotransmitter (Taheri et al., 2002; Thannickal et al., 2000). (That discovery has led to the clinical testing of a new sleeping pill that works by blocking orexin’s arousing activity.) Narcolepsy, it is now clear, is a brain disease; it is not just “in your mind.” And this gives hope that narcolepsy might be effectively relieved by a drug that mimics the missing orexin and can sneak through the blood-brain barrier (Fujiki et al., 2003; Siegel, 2000). In the meantime, physicians are prescribing other drugs to relieve narcolepsy’s sleepiness in humans.

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Although 1 in 20 of us have sleep apnea, it was unknown before modern sleep research. Apnea means “with no breath,” and people with this condition intermittently stop breathing during sleep. After an airless minute or so, decreased blood oxygen arouses them enough to snort in air for a few seconds, in a process that repeats hundreds of times each night, depriving them of slow-wave sleep. Apnea sufferers don’t recall these episodes the next day. So, despite feeling fatigued and depressed—and hearing their mate’s complaints about their loud “snoring”—many are unaware of their disorder (Peppard et al., 2006).

Sleep apnea is associated with obesity, and as the number of obese Americans has increased, so has this disorder, particularly among overweight men (Keller, 2007). Apnea-related sleep loss also contributes to obesity. In addition to loud snoring, other warning signs are daytime sleepiness, irritability, and (possibly) high blood pressure, which increases the risk of a stroke or heart attack (Dement, 1999). If one doesn’t mind looking a little goofy in the dark (imagine a snorkeler at a slumber party), the treatment—a masklike device with an air pump that keeps the sleeper’s airway open—can effectively relieve apnea symptoms. By so doing, it can also alleviate the depression symptoms that often accompany sleep apnea (Levine, 2012; Wheaton et al., 2012).

Unlike sleep apnea, night terrors target mostly children, who may sit up or walk around, talk incoherently, experience doubled heart and breathing rates, and appear terrified (Hartmann, 1981). They seldom wake up fully during an episode and recall little or nothing the next morning—at most, a fleeting, frightening image. Night terrors are not nightmares (which, like other dreams, typically occur during early morning REM sleep); night terrors usually occur during the first few hours of NREM-3.

Sleepwalking—another NREM-3 sleep disorder—and sleeptalking are usually childhood disorders and, like narcolepsy, they run in families. (Sleeptalking—usually garbled or nonsensical—can occur during any sleep stage [Mahowald & Ettinger, 1990].) Occasional childhood sleepwalking occurs for about one-third of those with a sleepwalking fraternal twin and half of those with a sleepwalking identical twin. The same is true for sleeptalking (Hublin et al., 1997, 1998). Sleepwalking is usually harmless. After returning to bed on their own or with the help of a family member, few sleepwalkers recall their trip the next morning. About 20 percent of 3- to 12-year-olds have at least one episode of sleepwalking, usually lasting 2 to 10 minutes; some 5 percent have repeated episodes (Giles et al., 1994). Young children, who have the deepest and lengthiest NREM-3 sleep, are the most likely to experience both night terrors and sleepwalking. As we grow older and deep NREM-3 sleep diminishes, so do night terrors and sleepwalking.

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Now playing at an inner theater near you: the premiere showing of a sleeping person’s vivid dream. This never-before-seen mental movie features captivating characters wrapped in a plot so original and unlikely, yet so intricate and so seemingly real, that the viewer later marvels at its creation.

Waking from a troubling dream (you were late to something and your legs weren’t working), who among us has not wondered about this weird state of consciousness? How can our brain so creatively, colorfully, and completely construct this alternative world? In the shadowland between our dreaming and waking consciousness, we may even wonder for a moment which is real.

Discovering the link between REM sleep and dreaming opened a new era in dream research. Instead of relying on someone’s hazy recall hours or days after having a dream, researchers could catch dreams as they happened. They could awaken people during or within 3 minutes after a REM sleep period and hear a vivid account.

3-10 What do we dream?

Daydreams tend to involve the familiar details of our life—perhaps picturing ourselves explaining to an instructor why a paper will be late, or replaying in our minds personal encounters we relish or regret. REM dreams are vivid, emotional, and often bizarre—so vivid we may confuse them with reality. Awakening from a nightmare, a 4-year-old may be sure there is a bear in the house.

We spend six years of our life in dreams, many of which are anything but sweet. For both women and men, 8 in 10 dreams are marked by at least one negative event or emotion (Domhoff, 2007). Common themes are repeatedly failing in an attempt to do something; being attacked, pursued, or rejected; or experiencing misfortune (Hall et al., 1982). Dreams with sexual imagery occur less often than you might think. In one study, only 1 in 10 dreams among young men and 1 in 30 among young women had sexual content (Domhoff, 1996).

More commonly, a dream’s story line incorporates traces of previous days’ non-sexual experiences and preoccupations (De Koninck, 2000):

Our two-track mind continues to monitor our environment while we sleep. Sensory stimuli—a particular odor or a phone’s ringing—may be instantly and ingeniously woven into the dream story. In a classic experiment, researchers lightly sprayed cold water on dreamers’ faces (Dement & Wolpert, 1958). Compared with sleepers who did not get the cold-water treatment, these people were more likely to dream about a waterfall, a leaky roof, or even about being sprayed by someone.

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So, could we learn a foreign language by hearing it played while we sleep? If only. While sleeping we can learn to associate a sound with a mild electric shock (and to react to the sound accordingly). We can also learn to associate a particular sound with a pleasant or unpleasant odor (Arzi et al., 2012). But we do not remember recorded information played while we are soundly asleep (Eich, 1990; Wyatt & Bootzin, 1994). In fact, anything that happens during the 5 minutes just before we fall asleep is typically lost from memory (Roth et al., 1988). This explains why sleep apnea patients, who repeatedly awaken with a gasp and then immediately fall back to sleep, do not recall the episodes. Ditto someone who awakens momentarily, sends a text message, but the next day can’t remembering doing so. It also explains why dreams that momentarily awaken us are mostly forgotten by morning. To remember a dream, get up and stay awake for a few minutes.

3-11 What functions have theorists proposed for dreams?

Dream theorists have proposed several explanations of why we dream, including these:

To satisfy our own wishes. In 1900, in his landmark book The Interpretation of Dreams, Sigmund Freud offered what he thought was “the most valuable of all the discoveries it has been my good fortune to make.” He proposed that dreams provide a psychic safety valve that discharges otherwise unacceptable feelings. He viewed a dream’s manifest content (the apparent and remembered story line) as a censored, symbolic version of its latent content, the unconscious drives and wishes that would be threatening if expressed directly. Although most dreams have no overt sexual imagery, Freud nevertheless believed that most adult dreams could be “traced back by analysis to erotic wishes.” Thus, a gun might be a disguised representation of a penis.

Freud considered dreams the key to understanding our inner conflicts. However, his critics say it is time to wake up from Freud’s dream theory, which is a scientific nightmare. Based on the accumulated science, “there is no reason to believe any of Freud’s specific claims about dreams and their purposes,” observed dream researcher William Domhoff (2003). Some contend that even if dreams are symbolic, they could be interpreted any way one wished. Others maintain that dreams hide nothing. A dream about a gun is a dream about a gun. Legend has it that even Freud, who loved to smoke cigars, acknowledged that “sometimes, a cigar is just a cigar.” Freud’s wish-fulfillment theory of dreams has in large part given way to other theories.

To file away memories. The information-processing perspective proposes that dreams may help sift, sort, and fix the day’s experiences in our memory. Some studies support this view. When tested the day after learning a task, those who had been deprived of both slow-wave and REM sleep did not do as well as those who had slept undisturbed (Stickgold, 2012). In other studies, people who heard unusual phrases or learned to find hidden visual images before bedtime remembered less the next morning if they had been awakened every time they began REM sleep than if awakened during other sleep stages (Empson & Clarke, 1970; Karni & Sagi, 1994).

Brain scans confirm the link between REM sleep and memory. The brain regions that buzzed as rats learned to navigate a maze, or as people learned to perform a visual-discrimination task, buzzed again during later REM sleep (Louie & Wilson, 2001; Maquet, 2001). So precise were these activity patterns that scientists could tell where in the maze the rat would be if awake. Some researchers dispute the dreaming-strengthens-memory idea, noting that REM sleep may support memory for reasons unrelated to dreaming. Also, memory consolidation may occur during non-REM sleep (Diekelmann & Born, 2010). This much seems true: A night of solid sleep (and dreaming) has an important place in our lives. To sleep, perchance to remember.

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This is important news for students, many of whom, observed researcher Robert Stickgold (2000), suffer from a kind of sleep bulimia—binge sleeping on the weekend. “If you don’t get good sleep and enough sleep after you learn new stuff, you won’t integrate it effectively into your memories,” he warned. That helps explain why high school students with high grades have averaged 25 minutes more sleep a night than their lower-achieving classmates (Wolfson & Carskadon, 1998; see FIGURE 3.18). Sacrificing sleep time to study actually worsens academic performance, by making it harder the next day to understand class material or do well on a test (Gillen-O’Neel et al., 2013).

To develop and preserve neural pathways. Perhaps dreams, or the brain activity associated with REM sleep, serve a physiological function, providing the sleeping brain with periodic stimulation. This theory makes developmental sense. As you will see in Chapter 5, stimulating experiences preserve and expand the brain’s neural pathways. Infants, whose neural networks are fast developing, spend much of their abundant sleep time in REM sleep (FIGURE 3.19).

To make sense of neural static. Other theories propose that dreams erupt from neural activation spreading upward from the brainstem (Antrobus, 1991; Hobson, 2003, 2004, 2009). According to “activation–synthesis theory,” dreams are the brain’s attempt to synthesize random neural activity. Much as a neurosurgeon can produce hallucinations by stimulating different parts of a patient’s cortex, so can stimulation originating within the brain. These internal stimuli activate brain areas that process visual images, but not the visual cortex area, which receives raw input from the eyes. As Freud might have expected, PET scans of sleeping people also reveal increased activity in the emotion-related limbic system (in the amygdala) during emotional dreams (Schwartz, 2012). In contrast, frontal lobe regions responsible for inhibition and logical thinking seem to idle, which may explain why our dreams are less inhibited than we are when awake (Maquet et al., 1996). Add the limbic system’s emotional tone to the brain’s visual bursts and—Voila!—we dream. Damage either the limbic system or the visual centers active during dreaming, and dreaming itself may be impaired (Domhoff, 2003).

To reflect cognitive development. Some dream researchers dispute both the Freudian and neural activation theories, preferring instead to see dreams as part of brain maturation and cognitive development (Domhoff, 2010, 2011; Foulkes, 1999). For example, prior to age 9, children’s dreams seem more like a slide show and less like an active story in which the dreamer is an actor. Dreams overlap with waking cognition and feature coherent speech. They simulate reality by drawing on our concepts and knowledge. They engage brain networks that also are active during daydreaming—and so may be viewed as intensified mind wandering, enhanced by visual imagery (Fox et al., 2013).

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Unlike the idea that dreams arise from bottom-up brain activation, the cognitive perspective emphasizes our mind’s top-down control of our dream content (Nir & Tononi, 2010). Dreams, says G. William Domhoff (2014), “dramatize our wishes, fears, concerns, and interests in striking scenarios that we experience as real events.” Given a healthy, mature brain, such mental simulations happen whenever there is (1) a loss of conscious attention, (2) an absence of external stimuli, and (3) sufficient brain activation, such as during REM sleep.

TABLE 3.2 compares these major dream theories. Although today’s sleep researchers debate dreams’ function—and some are skeptical that dreams serve any function—there is one thing they agree on: We need REM sleep. Deprived of it by repeatedly being awakened, people return more and more quickly to the REM stage after falling back to sleep. When finally allowed to sleep undisturbed, they literally sleep like babies—with increased REM sleep, a phenomenon called REM rebound. Withdrawing REM-suppressing sleeping medications also increases REM sleep, but with accompanying nightmares. Most other mammals also experience REM rebound, suggesting that the causes and functions of REM sleep are deeply biological. (That REM sleep occurs in mammals—and not in animals such as fish, whose behavior is less influenced by learning—fits the information-processing theory of dreams.)

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So does this mean that because dreams serve physiological functions and extend normal cognition, they are psychologically meaningless? Not necessarily. Every psychologically meaningful experience involves an active brain. We are once again reminded of a basic principle: Biological and psychological explanations of behavior are partners, not competitors.

Dreams are a fascinating altered state of consciousness. But they are not the only altered states. As we will see next, drugs also alter conscious awareness.

LEARNING OBJECTIVES

RETRIEVAL PRACTICE Take a moment to answer each of these Learning Objective Questions (repeated here from within this section). Then click the 'show answer' button to check your answers. Research suggests that trying to answer these questions on your own will improve your long-term retention (McDaniel et al., 2009).

3-4What is sleep?

3-5How do our biological rhythms influence our daily functioning?

3-6What is the biological rhythm of our sleeping and dreaming stages?

3-7How do biology and environment interact in our sleep patterns?

3-8What are sleep’s functions?

3-9How does sleep loss affect us, and what are the major sleep disorders?

3-10What do we dream?

3-11What functions have theorists proposed for dreams?

TERMS AND CONCEPTS TO REMEMBER

RETRIEVAL PRACTICE Match each of the terms on the left with its definition on the right. Click on the term first and then click on the matching definition. As you match them correctly they will move to the bottom of the activity.

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