Psychology: Module 8.3 Important Points

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.

Approximate time spent dreaming.

Obviously, then, we need sleep. Sleep commands roughly one-third of our lives—some 25 years, on average.

Approximate time spent sleeping in a lifetime.

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. Although the roar of my [ND's] neighborhood garbage truck leaves me undisturbed, my baby's cry will shatter my sleep. The sound of your name can also cause your unconscious body to perk up. EEG recordings confirm that the brain's auditory cortex responds to sound stimuli even during sleep (Kutas, 1990).

Awareness during Sleep.

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 awaken refreshed, sustain better moods, and perform more efficiently and accurately.

Benefits of unrestricted sleep.

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 (Dew et al., 2003; Parthasarathy et al., 2015; Scullin & Bliwise, 2015).

Sleep & long life.

Question: Does eating spicy foods cause us to dream more? Answer: Any food that causes you to awaken more increases your chance of recalling a dream (Moorcroft, 2003).

Food's effect on dreams.

Freud's wish-fulfillment Dreams provide a "psychic safety valve"—expressing otherwise unacceptable feelings; contain manifest (remembered) content and a deeper layer of latent content (a hidden meaning).

Freud's theory of dreams.

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).

Genital Arousal during REM sleep.

This is important news for students, many of whom, observed researcher Robert Stickgold (2000), suffer from a kind of sleep bulimia—sleep deprived on weekdays and 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 slept about 25 minutes longer each night than their lower-achieving classmates (Wolfson & Carskadon, 1998; see FIGURE 8.9).

Good sleep and memory.

And when you sleep, as when awake, you process most information outside your conscious awareness.

Information processing during sleep.

Dreams help us sort out the day's events and consolidate our memories.

Information-processing theory of dreams.

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 becomes worse when we fret about it. In laboratory studies, people with insomnia 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.

Insomnia explained.

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; Opp & Krueger, 2015).

Sleep & physical health.

After a succession of 5-hour nights, we accumulate a sleep debt that 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).

Sleep debts.

• Exercise regularly but not in the late evening. (Late afternoon is best.) • Avoid caffeine after early afternoon, and avoid food and drink near bedtime. The exception would be a glass of milk, which provides raw materials for the manufacture of serotonin, a neurotransmitter that facilitates sleep. • Relax before bedtime, using dimmer light.

Some natural sleep Aids.

• Sleep on a regular schedule (rise at the same time even after a restless night) and avoid long naps. • Hide time displays so you aren't tempted to check repeatedly. • Reassure yourself that temporary sleep loss causes no great harm. • Focus your mind on nonarousing, engaging thoughts, such as song lyrics or vacation travel (Gellis et al., 2013). • If all else fails, settle for less sleep, either going to bed later or getting up earlier.

Some natural sleep Aids.

A regular full night's sleep can "dramatically improve your athletic ability," report James Maas and Rebecca Robbins (2010). REM sleep and NREM-2 sleep—which occur mostly in the final hours of a long night's sleep—also help strengthen the neural connections that build enduring memories, including the "muscle memories" learned while practicing tennis or shooting baskets. Sleep promotes both a strong body and a strong mind. 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.

Sleep & Athletics.

Horses, which spend 92 percent of each day standing and can sleep standing, must lie down for REM sleep (Morrison, 2003).

REM sleep in horses.

Rapid eye movements also stir the liquid behind the cornea; this delivers fresh oxygen to corneal cells, preventing their suffocation.

REM sleep's effect on the eyes.

Dreams aren't real, but REM sleep tricks your brain into responding as if you are actually watching a real scene (Andrillon et al., 2015).

REM sleeps effect on the brain through dreams.

ANSWER: With each soldier cycling through the sleep stages independently, it is very likely that at any given time at least one will be in an easily awakened stage in the event of a threat.

RP-1 Why would communal sleeping provide added protection for those whose safety depends upon vigilance, such as these soldiers (above)?

ANSWER: REM, NREM-1, NREM-2, NREM-3; normally we move through NREM-1, then NREM-2, then NREM-3, then back up through NREM-2 before we experience REM sleep.

RP-2 What are the four sleep stages, and in what order do we normally travel through those stages?

ANSWER: (1) Sleep has survival value. (2) Sleep helps us restore the immune system and repair brain tissue. (3) During sleep we consolidate memories. (4) Sleep fuels creativity. (5) Sleep plays a role in the growth process.

RP-5 What are five proposed reasons for our need for sleep?

ANSWER: (1) Freud's wish-fulfillment (dreams as a psychic safety valve), (2) information-processing (dreams sort the day's events and consolidate memories), (3) physiological function (dreams pave neural pathways), (4) activation-synthesis (REM sleep triggers random neural activity that the mind weaves into stories), and (5) cognitive development (dreams reflect the dreamer's developmental stage)

RP-7 What five theories propose explanations for why we dream?

1 in 10 adults; 1 in 4 older adults.

Rate of Insomnia.

1 in 2000 adults.

Rate of Narcolepsy.

1 in 100 adults; 1 in 30 children.

Rate of Night terrors.

1 in 20 adults.

Rate of Sleep apnea.

1-15 in 100 in the general population for sleepwalking (NSF, 2016b); about half of young children for sleeptalking (Reimão & Lefévre, 1980)

Rate of Sleepwalking and sleeptalking.

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).

Recording of information while sleeping.

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.

Remembering a dream.

Compared with nonmusicians, musicians report twice as many dreams of music (Uga et al., 2006).

Storylines of the dreams of musicians.

RP-3 Can you match the cognitive experience with the sleep stage? 1. NREM-1 2. NREM-3 3. REM a. story-like dream b. fleeting images c. minimal awareness

ANSWER: 1. b, 2. c, 3. a

RP-6 A well-rested person would be more likely to have __________ (trouble concentrating/quick reaction times) and a sleep-deprived person would be more likely to __________ (gain weight/fight off a cold).

ANSWER: quick reaction times; gain weight

RP-4 The __________ nucleus helps monitor the brain's release of melatonin, which affects our __________ rhythm.

ANSWER: suprachiasmatic, circadian

REM sleep triggers neural activity that evokes random visual memories, which our sleeping brain weaves into stories.

Activation-synthesis theory of dreams.

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).

Changes in Circadian Rhythm.

As morning nears, body temperature rises; it then peaks during the day, dips for a time in early afternoon (when many people take siestas or drink a caffeinated beverage), and begins to drop again in the evening. Thinking and memory improve as we approach 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 alertness when your normal wake-up time arrives.

Circadian Rhythm explained.

Dream content reflects dreamers' level of cognitive development—their knowledge and understanding. Dreams simulate our lives, including worst-case scenarios.

Cognitive development theory of dreams.

"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."

Consequences of sleep deprivation.

Lacks any scientific support; dreams may be interpreted in many different ways.

Critical consideration for Freud's theory of dreams.

The individual's brain is weaving the stories, which still tells us something about the dreamer.

Critical considerations for Activation-synthesis theory of dreams.

Does not propose an adaptive function of dreams.

Critical considerations for Cognitive development theory of dreams.

But why do we sometimes dream about things we have not experienced and about past events?

Critical considerations for Information-processing theory of dreams.

This does not explain why we experience meaningful dreams.

Critical considerations for Physiological function theory of dreams.

True or false? "Everyone needs 8 hours of sleep." False. 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 nightly sleep periods—sometimes called "first sleep" and "second sleep" (Randall, 2012). And some find that a 15-minute midday nap is as effective as another hour of nighttime sleep (Horne, 2011).

Differing Sleep needs.

This fact came to light when 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 machine 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).

Discovery of REM sleep. Eugene Aserinsky & his yr old son, Armond (1952).

In sleep lab studies, 37 percent of participants have reported rarely or never having dreams that they "can remember the next morning" (Moore, 2004). Yet even they, more than 80 percent of the time, could recall a dream after being awakened during REM sleep.

Dream Recall.

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.

Effect of sleep loss in a nutshell.

Chronic tiredness. Reliance on sleeping pills and alcohol, which reduce REM sleep and lead to tolerance—a state in which increasing doses are needed to produce an effect.

Effects of Insomnia.

Risk of falling asleep at a dangerous moment. Narcolepsy attacks usually last less than 5 minutes, but they can happen at the worst and most emotional times. Everyday activities, such as driving, require extra caution.

Effects of Narcolepsy.

Doubling of a child's heart and breathing rates during the attack. Luckily, children remember little or nothing of the fearful event the next day. As people age, night terrors become more and more rare.

Effects of Night terrors.

Fatigue and depression (as a result of slow-wave sleep deprivation). Associated with obesity (especially among men).

Effects of Sleep apnea.

Few serious concerns. Sleepwalkers return to their beds on their own or with the help of a family member, rarely remembering their trip the next morning.

Effects of Sleepwalking and sleeptalking.

Yawning, which is also socially contagious, stretches your neck muscles and increases your heart rate, which increases your alertness

Effects of Yawning.

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.

Effects of drugs on insomnia.

.Being bathed in (or deprived of) light disrupts our 24-hour biological clock (Czeisler et al., 1999; Dement, 1999). Night-shift workers may experience a chronic state of desynchronization. As a result, they become more likely to develop fatigue, stomach problems, heart disease, and, for women, breast cancer (Knutsson & Bøggild, 2010; Lin et al., 2015; Puttonen et al., 2009).

Effects of light on the biological clock.

One study of Stanford University men's basketball players found that when their average sleep increased 110 minutes per night over the course of several weeks, their sprint times decreased, and their free throw and 3-point shooting percentages both increased 9 percent (Mah et al., 2011).

Example of the benefits of sleep to athletics.

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.

Experiment that observed the moment of sleep, by William Dement (1999).

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 readjusting after a trip to California, 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).

Jet lag explained.

It decreases metabolic rate, a gauge of energy use (Buxton et al., 2012).

Lack of sleep & weight gain.

It enhances limbic brain responses to the mere sight of food and decreases cortical responses that help us resist temptation (Benedict et al., 2012; Greer et al., 2013; St-Onge et al., 2012).

Lack of sleep & weight gain.

It increases production of cortisol, a stress hormone that stimulates the body to make fat.

Lack of sleep & weight gain.

Lack of sleep can also make you gain weight. Sleep deprivation increases ghrelin, a hunger-arousing hormone, and decreases its hunger-suppressing partner, leptin (Shilsky et al., 2012).

Lack of sleep & weight gain.

Sleep researchers measure brain-wave activity, eye movements, and muscle tension with electrodes that pick up weak electrical signals from the brain (electrodes taped to the scalp), eyes (electrodes are taped just outside the corners of the eyes), and facial muscles (Electrodes taped on the chin) (Dement, 1978). Other devices will record your heart rate, respiration rate, and genital arousal.

Measuring Sleep Activity.

Adults, children, and infants trained to perform tasks therefore recall them better after a night's sleep, or even after a short nap, than after several hours awake (Friedrich et al., 2015; Seehagen et al., 2015). Older adults' more frequently disrupted sleep also disrupts memory consolidation (Boyce et al., 2016; Pace-Schott & Spencer, 2011). After sleeping well, older people remember more of recently learned material (Drummond, 2010).

Memory restoration in sleep explained.

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 occasional erectile difficulties get sleep-related erections, suggesting the problem is not between their legs.

Morning erections, and erections during sleep.

During REM sleep, your brain's motor cortex is active, 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.

Movement during REM sleep.

This 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.

NREM-1 sleep.

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.

NREM-2 Sleep.

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 this stage that children may wet the bed.)

NREM-3 Sleep.

In general, night owls tend to be smart and creative (Giampietro & Cavallera, 2007). Morning types tend to do better in school, take more initiative, be more punctual, and be less vulnerable to depression (Preckel et al., 2013; Randler, 2008, 2009; Werner et al., 2015).

Night owls vs Morning Larks.

After suffering a trauma, people commonly report nightmares, which help extinguish daytime fears (Levin & Nielsen, 2007, 2009).

Nightmare storylined dreams.

Sleep talking can occur during any sleep stage. Sleepwalking happens in NREM-3 sleep.

Occurrence of Sleepwalking & Sleep talking.

Regular brain stimulation from REM sleep may help develop and preserve neural pathways.

Physiological function theory of dreams.

We need REM sleep. Deprived of it by repeated awakenings, 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.

REM rebound explained.

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 (Perkinson-Gloor et al., 2013; Winsler et al., 2015).

REM sleep & depression.

Brain scans confirm the link between REM sleep and memory. The brain regions that were active as rats learned to navigate a maze, or as people learned to perform a visual-discrimination task, became active again later during 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. To sleep, perchance to remember.

REM sleep & memory.

People rarely snore during dreams. When REM starts, snoring stops.

REM sleep & snoring.

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. Drowsy driving has contributed to an estimated one in six American traffic accidents (AAA, 2010) and to some 30 percent of Australian highway deaths (Maas, 1999).

Sleep deprivation & slowed reactions.

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

Sleep deprivation in students.

Dolphins, porpoises, and whales sleep with one side of their brain at a time (Miller et al., 2008).

Sleep in some marine mammals.

Sleep loss is also a predictor of depression (Baglioni et al., 2016). 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).

Sleep loss & depression.

This fits a broader principle: A species' sleep pattern tends to suit its ecological niche (Siegel, 2009). Animals with the greatest need to graze and the least ability to hide tend to sleep less. Animals also sleep less, with no ill effects, during times of mating and migration (Siegel, 2012). (For a sampling of animal sleep times, see FIGURE 8.6.)

Sleep patterns for protection in some animals.

Think of it this way: When consciousness leaves your house, workers come in to clean, saying "Good night. Sleep tidy."

Sleep recuperation in a nutshell.

Sleep, it seems, strengthens memories in a way that being awake does not.

Sleep strengthens Memories.

Studies in four countries have found blind people mostly dreaming of using their nonvisual senses (Buquet, 1988; Taha, 1972; Vekassy, 1977). But even natively blind people sometimes "see" in their dreams (Bértolo, 2005). Likewise, people born paralyzed below the waist sometimes dream of walking, standing, running, or cycling (Saurat et al., 2011; Voss et al., 2011).

Storylines of the dreams of the disabled.

Psychologists have discovered a treatment that strengthens memory, increases concentration, boosts mood, moderates hunger, reduces obesity, fortifies the 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 until you feel more like a rested and energized student and less like a zombie.

The amazing treatment for sleep deprivation!

We spend six years of our life in dreams, many of which are anything but sweet.

The amount of time spent dreaming.

For both women and men, 8 in 10 dreams are marked by at least one negative event or emotion (Domhoff, 2007). Common themes include 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).

The contents of dreams.

Light striking the retina signals the suprachiasmatic nucleus (SCN) to suppress the pineal gland's production of the sleep hormone melatonin. At night, the SCN quiets down, allowing the pineal gland to release melatonin into the bloodstream.

The cycle of the biological clock.

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).

The effect of sleep sacrifice for studying.

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.

The environment's effect on dreams.

Today, more than ever, our sleep patterns leave us not only sleepy but drained of energy and feelings of well-being. This tiredness tendency has grown so steadily that some researchers have labeled current times the "Great Sleep Recession" (Keyes et al., 2015)

The great sleep recession.

The sleep cycle repeats itself about every 90 minutes for younger adults (with shorter, more frequent cycles for older adults). As the night goes on, deep NREM-3 sleep grows shorter and disappears, and REM and NREM-2 sleep periods get longer (see Figure 8.4). By morning, we have spent 20 to 25 percent of an average night's sleep—some 100 minutes—in REM sleep.

The length of the sleep cycle.

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).

The limbic systems role in dreams.

Whether for work or play, bright 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 (FIGURE 8.5). 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 (Chang et al., 2015; Gandhi et al., 2015).

The melatonin pathway.

More commonplace is the boost that a complete night's sleep gives to our thinking and learning. After working on a task, then sleeping on it, people solve difficult problems more insightfully than do those who stay awake (Barrett, 2011; Sio et al., 2013). They also are better at spotting connections among novel pieces of information (Ellenbogen et al., 2007; Whitehurst et al., 2016).

The mental boost of Sleep.

To think smart and see connections, it often pays to ponder a problem just before bed and then sleep on it.

The mental boost of sleep in a nutshell.

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. Approximately 90 percent of Americans report using a light-emitting electronic device one hour before going to sleep (Chang et al., 2015). Such artificial light delays sleep.

The modern 25-hour body clock.

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'll ultimately spend about half your night), you enter the most intriguing of the four sleep phases—REM sleep (FIGURE 8.4). 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.

The sleep cycle to REM sleep.

A popular sleep myth: If you dream you are falling and hit the ground (or if you dream of dying), you die. Unfortunately, those who could confirm these ideas are not around to do so. Many people, however, have had such dreams and are alive to report them.

The sleep myth of the he reality of dreams.

People pass through a multistage sleep cycle several times each night, with the periods of deep sleep diminishing and REM sleep periods increasing in duration. As people age, sleep becomes more fragile, with awakenings common among older adults (Kamel & Gammack, 2006; Neubauer, 1999).

The stages in a typical night's sleep.

More commonly, a dream's storyline incorporates traces of previous days' nonsexual experiences and preoccupations (De Koninck, 2000):

The storylines of dreams.

The beta waves of an alert, waking state and the regular alpha waves of an awake, relaxed state differ from the slower, larger delta waves of deep NREM-3 sleep. Although the rapid REM sleep waves resemble the near-waking NREM-1 sleep waves, the body is more internally aroused during REM sleep than during NREM (non-REM) sleep.

The waves of the different sleep stages.

Sleep patterns are genetically influenced. Researchers are tracking the sleep-regulating genes in humans and other animals (Hayashi et al., 2015; Mackenzie et al., 2015). Sleep patterns are also culturally influenced. In Britain, Canada, Germany, Japan, and the United States, adults average 7 hours of sleep a night on workdays, and 7 to 8 hours on other days (NSF, 2013). The weeknight sleep of many students and workers falls short of this average, however (NSF, 2008). Earlier school start times, more extracurricular activities, and a lack of parent-set bedtime leads American adolescents to get less sleep than their Australian counterparts (Short et al., 2013). Thanks to modern lighting, shift work, and social media diversions, many who might have gone to bed at 9:00 P.M. a century ago are now up until 11:001 P.M. or later. With sleep, as with waking behavior, biology and environment interact.

Variable sleep patterns.

Freud considered dreams the key to understanding our inner conflicts.

What Freud considered dreams to be.

Sleep feeds creative thinking. Dreams can inspire noteworthy artistic and scientific achievements,

Why Do We Sleep?

Sleep helps restore and rebuild our fading memories of the day's experiences. To sleep is to strengthen. Sleep consolidates our memories by replaying recent learning and strengthening neural connections (Pace-Schott et al., 2015; Yang et al., 2014). It reactivates recent experiences stored in the hippocampus and shifts them for permanent storage elsewhere in the cortex (Racsmány et al., 2010; Urbain et al., 2016).

Why Do We Sleep?

Sleep helps us recuperate. Sleep helps restore the immune system and repair brain tissue. Sleep gives resting neurons time to repair themselves, while pruning or weakening unused connections (Ding et al., 2016).

Why Do We Sleep?

Sleep protects. When darkness shut down the day's hunting, gathering, and travel, our distant ancestors were better off asleep in a cave, out of harm's way. Those who didn't wander around dark cliffs were more likely to leave descendants.

Why Do We Sleep?

Sleep supports growth. During slow-wave sleep, which occurs mostly in the first half of a night's sleep, the pituitary gland releases a growth hormone that is necessary for muscle development.

Why Do We Sleep?