What are the five common beliefs about dreaming?

Sleep, Dreaming, and Circadian Rhythms How Much Do You Need to Sleep?

14.1 Stages of Sleep

14.2 Why Do We Sleep, and Why Do We Sleep When We Do?

14.3 Effects of Sleep Deprivation

14.4 Circadian Sleep Cycles

14.5 Four Areas of the Brain Involved in Sleep

14.6 Drugs That Affect Sleep

14.7 Sleep Disorders

14.8 Effects of Long-Term Sleep Reduction

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Even though she is now retired she is still busy in the community, helping sick friends whenever requested. She is an active painter and . . . writer. Although she becomes tired physically, when she needs to sit down to rest her legs, she does not ever report feeling sleepy. During the night she sits on her bed . . . reading, writing, crocheting or painting. At about 2:00 A.M. she falls asleep without any preceding drowsiness often while still holding a book in her hands. When she wakes about an hour later, she feels as wide awake as ever. . . .

We invited her along to the laboratory. She came will- ingly but on the first evening we hit our first snag. She an- nounced that she did not sleep at all if she had interesting things to do, and by her reckoning a visit to a university sleep laboratory counted as very interesting. Moreover, for the first time in years, she had someone to talk to for the whole of the night. So we talked.

In the morning we broke into shifts so that some could sleep while at least one person stayed with her and entertained her during the next day. The second night was a repeat performance of the first night. . . .

In the end we prevailed upon her to allow us to apply EEG electrodes and to leave her sitting comfortably on the bed in the bedroom. She had promised that she would co-operate by not resisting sleep although she claimed not to be especially tired. . . . At approximately 1:30 A.M., the EEG record showed the first signs of sleep even though . . . she was still sitting with the book in her hands. . . .

The only substantial difference between her sleep and what we might have expected. . . was that it was of short duration. . . . [After 99 minutes], she had no further inter- est in sleep and asked to . . . join our company again.

14.1 Stages of Sleep

Many changes occur in the body during sleep. This section introduces you to the major ones.

Three Standard Psychophysiological Measures of Sleep There are major changes in the human EEG during the course of a night’s sleep. Although the EEG waves that ac- company sleep are generally high-voltage and slow, there are periods throughout the night that are dominated by low- voltage, fast waves similar to those in nonsleeping individuals. In the 1950s, it was discovered that rapid eye movements (REMs) occur under the closed eyelids of sleepers during these periods of low-voltage, fast EEG activity. And in 1962,

Most of us have a fondness for eating and sex—the two highly esteemed motivated behaviorsdiscussed in Chapter 12 and 13. But the amount of time devoted to these behaviors by even the most amorous gourmands pales in comparison to the amount of time spent sleeping: Most of us will sleep for well over 175,000 hours in our lifetimes. This extraordinary com- mitment of time implies that sleep fulfills a critical biolog- ical function. But what is it? And what about dreaming: Why do we spend so much time dreaming? And why do we tend to get sleepy at about the same time every day? Answers to these questions await you in this chapter.

Almost every time I lecture about sleep, somebody asks “How much sleep do we need?” Each time, I provide the same unsatisfying answer: I explain that there are two fun-

damentally different answers to this question, but neither has emerged a clear winner.

One answer stresses the presumed health-promoting and recuperative powers of sleep and suggests that people need as much sleep as they can comfortably get—the usual prescription being at least 8 hours per night. The other answer is that many of us sleep more than we need to and are consequently sleeping part of our life away. Just think how your life could change if you slept 5 hours per night instead of 8. You would have an extra 21 waking hours each week, a mind-boggling 10,952 hours each decade.

As I prepared to write this chapter, I began to think of the personal implications of the idea that we get more sleep than we need. That is when I decided to do some-

thing a bit unconventional. I am going to participate in a sleep-reduction experiment—by trying to get no more

than 5 hours of sleep per night—11:00 P.M. to 4:00 A.M.— until this chapter is written. As I begin, I am excited by the prospect of having more time to write, but a little worried that this extra time might cost me too dearly.

It is now the next day—4:50 Saturday morning to be exact—and I am just sitting down to write. There was a party last night, and I didn’t make it to bed by 11:00; but considering that I slept for only 3 hours and 35 minutes, I feel quite good. I wonder what I will feel like later in the day. In any case, I will report my experiences to you at the end of the chapter.

The following case study challenges several common beliefs about sleep. Ponder its implications before pro- ceeding to the body of the chapter.

The Case of the Woman Who Wouldn’t Sleep Miss M . . . is a busy lady who finds her ration of twenty- three hours of wakefulness still insufficient for her needs.

356 Chapter 14 ■ Sleep, Dreaming, and Circadian Rhythms

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Berger and Oswald discovered that there is also a loss of elec- tromyographic activity in the neck muscles during these same sleep periods. Subsequently, the electroencephalo- gram (EEG), the electrooculogram (EOG), and the neck electromyogram (EMG) became the three standard psy- chophysiological bases for defining stages of sleep.

Figure 14.1 depicts a volunteer participating in a sleep experiment. A participant’s first night of sleep in a labo- ratory is often fitful. That’s why the usual practice is to have each participant sleep several nights in the labora- tory before commencing a sleep study. The disturbance of sleep observed during the first night in a sleep laboratory is called the first-night phenomenon. It is well known to graders of introductory psychology examinations because of the creative definitions of it that are offered by students who forget that it is a sleep-related, rather than a sex-related, phenomenon.

Four Stages of Sleep EEG There are four stages of sleep EEG: stage 1, stage 2, stage 3, and stage 4. Examples of these are presented in Figure 14.2.

After the eyes are shut and a person prepares to go to sleep, alpha waves—waxing and wan- ing bursts of 8- to 12-Hz EEG waves—begin to punctuate the low-voltage, high-frequency waves of alert wakefulness. Then, as the person falls asleep, there is a sud- den transition to a period of stage 1 sleep EEG. The stage 1 sleep EEG is a low-voltage, high- frequency signal that is similar to, but slower than, that of alert wakefulness.

There is a gradual increase in EEG voltage and a decrease in EEG frequency as the person pro- gresses from stage 1 sleep through stages 2, 3, and 4. Accordingly, the stage 2 sleep EEG has a slightly

35714.1 ■ Stages of Sleep

Alert wakefulness

Just before sleep

Stage 1

Stage 2

Stage 3

Stage 4

K complexSleep spindle

Alpha waves

FIGURE 14.1 A participant in a sleep experiment.

FIGURE 14.2 The EEG of alert wakefulness, the EEG that precedes sleep onset, and the four stages of sleep EEG. Each trace is about 10 seconds long.

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higher amplitude and a lower frequency than the stage 1 EEG; in addition, it is punctuated by two characteristic wave forms: K complexes and sleep spindles. Each K com-

plex is a single large negative wave (upward deflection) fol- lowed immediately by a single

large positive wave (downward deflection)—see Cash and colleagues (2009). Each sleep spindle is a 1- to 2-second waxing and waning burst of 12- to 14-Hz waves. The stage 3 sleep EEG is defined by the occasional presence of delta waves—the largest and slowest EEG waves, with a fre- quency of 1 to 2 Hz—whereas the stage 4 sleep EEG is de- fined by a predominance of delta waves.

Once sleepers reach stage 4 EEG sleep, they stay there for a time, and then they retreat back through the stages of sleep to stage 1. However, when they return to stage 1, things are not at all the same as they were the first time through. The first period of stage 1 EEG during a night’s sleep (initial stage 1 EEG) is not marked by any striking electromyographic or electrooculographic changes, whereas subsequent periods of stage 1 sleep EEG (emergent stage 1 EEG) are accompanied by REMs and by a loss of tone in the muscles of the body core.

After the first cycle of sleep EEG—from initial stage 1 to stage 4 and back to emergent stage 1—the rest of the night is spent going back and forth through the stages. Figure 14.3 illustrates the EEG cycles of a typical night’s sleep and the close relation between emergent stage 1 sleep, REMs, and the loss of tone in core muscles. Notice that each cycle tends to be about 90 minutes long and that, as the night progresses, more and more time is spent in emergent stage 1 sleep, and less and less time is spent in the other stages, particularly stage 4. Notice also that there are brief periods during the night when the person is awake, although he or she usually does not remember these periods of wakefulness in the morning.

Let’s pause here to get some sleep-stage terms straight. The sleep associated with emergent stage 1 EEG is usually called REM sleep (pronounced “rehm”), after the associated rapid eye movements; whereas all other stages of sleep together are called NREM sleep (non-REM sleep). Stages 3 and 4 together are referred to as slow-wave sleep (SWS), after the delta waves that characterize them.

REMs, loss of core-muscle tone, and a low-amplitude, high-frequency EEG are not the only physiological corre- lates of REM sleep. Cerebral activity (e.g., oxygen con- sumption, blood flow, and neural firing) increases to waking levels in many brain structures, and there is a gen- eral increase in the variability of autonomic nervous sys- tem activity (e.g., in blood pressure, pulse, and respiration). Also, the muscles of the extremities occasionally twitch, and there is often some degree of penile erection in males.

REM Sleep and Dreaming Nathaniel Kleitman’s laboratory was an exciting place in 1953. REM sleep had just been discovered, and Kleitman and his students were driven by the fascinating implica- tion of the discovery. With the exception of the loss of tone in the core muscles, all of the other measures sug- gested that REM sleep episodes were emotion-charged. Could REM sleep be the physiological correlate of dream- ing? Could it provide researchers with a window into the subjective inner world of dreams? The researchers began by waking a few sleepers in the middle of REM episodes:

The vivid recall that could be elicited in the middle of the night when a subject was awakened while his eyes were moving rapidly was nothing short of miraculous. It [seemed to open] . . . an exciting new world to the subjects whose only previous dream memories had been the vague morning-after recall. Now, instead of perhaps some fleet- ing glimpse into the dream world each night, the subjects could be tuned into the middle of as many as ten or twelve dreams every night. (From Some Must Watch While Some Must Sleep by William C. Dement, Portable Stanford Books, Stanford Alumni Association, Stanford University, 1978, p. 37. Used by permission of William C. Dement.)

Strong support for the theory that REM sleep is the phys- iological correlate of dreaming came from the observation that 80% of awakenings from REM sleep but only 7% of awakenings from NREM (non-REM) sleep led to dream recall. The dreams recalled from NREM sleep tended to

358 Chapter 14 ■ Sleep, Dreaming, and Circadian Rhythms

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Stage 3

Stage 2

Stage 1

Awake Periods of REM Lack of core-muscle tone

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FIGURE 14.3 The course of EEG stages during a typical night’s sleep and the relation of emergent stage 1 EEG to REMs and lack of tone in core muscles.

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be isolated experiences (e.g., “I was falling”), while those associated with REM sleep tended to take the form of sto- ries, or narratives. The phenomenon of dreaming, which

for centuries had been the subject of wild speculation, was finally rendered accessi-

ble to scientific investigation.

Testing Common Beliefs about Dreaming The high correlation between REM sleep and dream re- call provided an opportunity to test some common be- liefs about dreaming. The following five beliefs were among the first to be addressed:

● Many people believe that external stimuli can become incorporated into their dreams. Dement and Wolpert (1958) sprayed water on sleeping volunteeers after

they had been in REM sleep for a few minutes, and then awakened them

a few seconds later. In 14 of 33 cases, the water was in- corporated into the dream report. The following narra- tive was reported by one participant who had been dreaming that he was acting in a play:

I was walking behind the leading lady when she sud- denly collapsed and water was dripping on her. I ran over to her and water was dripping on my back and head. The roof was leaking. . . . I looked up and there was a hole in the roof. I dragged her over to the side of the stage and began pulling the curtains. Then I woke up. (p. 550)

● Some people believe that dreams last only an instant, but research suggests that dreams run on “real time.” In one study (Dement & Kleitman, 1957), volunteers were awakened 5 or 15 minutes after the beginning of a REM episode and asked to decide on the basis of the duration of the events in their dreams whether they had been dreaming for 5 or 15 minutes. They were correct in 92 of 111 cases.

● Some people claim that they do not dream. However, these people have just as much REM sleep as normal dreamers. Moreover, they report dreams if they are awakened during REM episodes (Goodenough et al., 1959), although they do so less frequently than do normal dreamers.

● Penile erections are commonly assumed to be indica- tive of dreams with sexual content. However, erections are no more complete during dreams with frank sexual content than during those without it (Karacan et al., 1966). Even babies have REM-related penile erections.

● Many people believe that sleeptalking (somniloquy) and sleepwalking (somnambulism) occur only during dream- ing. This is not so (see Dyken, Yamada, & Lin-Dyken, 2001). Sleeptalking has no special association with REM sleep—it can occur during any stage but often occurs

during a transition to wakefulness. Sleepwalking usually occurs during stage 3 or 4 sleep, and it never occurs during dreaming, when core muscles tend to be totally relaxed (Usui et al., 2007). There is no proven treat- ment for sleepwalking (Harris & Grunstein, 2008).

Interpretation of Dreams Sigmund Freud believed that dreams are triggered by un- acceptable repressed wishes, often of a sexual nature. He ar- gued that because dreams represent unacceptable wishes, the dreams we experience (our manifest dreams) are merely disguised versions of our real dreams (our latent dreams): He hypothesized an unconscious censor that disguises and subtracts information from our real dreams so that we can endure them. Freud thus concluded that one of the keys to understanding people and dealing with their psychological problems is to expose the meaning of their latent dreams through the interpretation of their manifest dreams.

There is no convincing evidence for the Freudian the- ory of dreams; indeed, the brain science of the 1890s, which served as its foundation, is now obsolete. Yet many people accept the notion that dreams bubble up from a troubled subconscious and that they represent repressed thoughts and wishes.

The modern alternative to the Freudian theory of dreams is Hobson’s (1989) activation-synthesis theory (see Eiser, 2005). It is based on the observation that, dur- ing REM sleep, many brain-stem circuits become active and bombard the cerebral cortex with neural signals. The essence of the activation-synthesis theory is that the in- formation supplied to the cortex during REM sleep is largely random and that the resulting dream is the cor- tex’s effort to make sense of these random signals.

14.2 Why Do We Sleep, and Why Do We Sleep When We Do?

Now that you have been introduced to the properties of sleep and its various stages, the focus of this chapter shifts to a consideration of two fundamental questions about sleep: Why do we sleep? And why do we sleep when we do?

Two kinds of theories for sleep have been proposed: recuperation theories and adaptation theories. The differ- ences between these two theoretical approaches are re- vealed by the answers they offer to the two fundamental questions about sleep.

The essence of recuperation theories of sleep is that being awake disrupts the homeostasis (internal physio- logical stability) of the body in some way and sleep is re- quired to restore it. Various recuperation theories differ in terms of the particular physiological disruption they

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propose as the trigger for sleep—for example, it is com- monly believed that the function of sleep is to restore en- ergy levels. However, regardless of the particular function postulated by restoration theories of sleep, they all imply that sleepiness is triggered by a deviation from home- ostasis caused by wakefulness and that sleep is termi- nated by a return to homeostasis.

The essence of adaptation theories of sleep is that sleep is not a reaction to the disruptive effects of being awake but the result of an internal 24-hour timing mechanism—that is, we humans are programmed to sleep at night regardless of what happens to us during the day. According to these theories, we have evolved to sleep at night because sleep protects us from accident and pre- dation during the night. (Remember that humans evolved long before the advent of artificial lighting.)

Adaptation theories of sleep focus more on when we sleep than on the function of sleep. Some of these theo- ries even propose that sleep plays no role in the efficient physiological functioning of the body. According to these theories, early humans had enough time to get their eat-

ing, drinking, and reproducing out of the way during the daytime, and their strong motivation to sleep at night evolved to

conserve their energy resources and to make them less susceptible to mishap (e.g., predation) in the dark (Rattenborg, Martinez-Gonzales, & Lesku, 2009; Siegel, 2009). Adaptation theories suggest that sleep is like repro- ductive behavior in the sense that we are highly motivated to engage in it, but we don’t need it to stay healthy.

Comparative Analysis of Sleep Sleep has been studied in only a small number of species, but the evidence so far suggests that most mammals and birds sleep. Furthermore, the sleep of mammals and birds, like ours, is characterized by high-amplitude, low- frequency EEG waves punctuated by periods of low- amplitude, high-frequency waves (see Siegel, 2008). The

evidence for sleep in amphibians, reptiles, fish, and insects is less clear: Some display periods of inactivity and unresponsive-

ness, but the relation of these periods to mammalian sleep has not been established (see Siegel, 2008; Zimmerman et al., 2008). Table 14.1 gives the average number of hours per day that various mammalian species spend sleeping.

The comparative investigation of sleep has led to several important conclusions. Let’s consider four of these.

First, the fact that most mammals and birds sleep sug- gests that sleep serves some important physiological function, rather than merely protecting animals from mishap and conserving energy. The evidence is strongest in species that are at increased risk of predation when they sleep (e.g., antelopes) and in species that have evolved complex mechanisms that enable them to sleep.

For example, some marine mammals, such as dolphins, sleep with only half of their brain at a time so that the other half can control resurfacing for air (see Rattenborg, Amlaner, & Lima, 2000). It is against the logic of natural selection for some animals to risk predation while sleep- ing and for others to have evolved complex mechanisms to permit them to sleep, unless sleep itself serves some critical function.

Second, the fact that most mammals and birds sleep suggests that the primary function of sleep is not some special, higher-order human function. For example, sug- gestions that sleep helps humans reprogram our complex brains or that it permits some kind of emotional release to maintain our mental health are improbable in view of the comparative evidence.

Third, the large between-species differences in sleep time suggest that although sleep may be essential for sur- vival, it is not necessarily needed in large quantities (refer to Table 14.1). Horses and many other animals get by quite nicely on 2 or 3 hours of sleep per day. Moreover, it is important to realize that the sleep patterns of mammals and birds in their natural environments can vary substan- tially from their patterns in captivity, which is where they are typically studied (see Horne, 2009). For example, some animals that sleep a great deal in captivity sleep lit- tle in the wild when food is in short supply or during pe- riods of migration (Siegel, 2008).

360 Chapter 14 ■ Sleep, Dreaming, and Circadian Rhythms

Evolutiona Evolutionary Perspective Perspective

TABLE 14.1 Average Number of Hours Slept per Day by Various Mammalian Species

Hours of Sleep Mammalian Species per Day

Giant sloth 20

What are the five common beliefs about dreaming?

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