An Introduction to Psychology:
The Science of Mind and Behavior

How Much Sleep Do You Need?

As one last example of the difference between group averages and variances, let’s try to answer the following question: how much sleep do you need per night? On average, American adults get about 8 hours of sleep per night. So you might answer with confidence: “I need about 8 hours of sleep per night.” What is the problem with this answer? Actually, there are three problems with this answer. It confuses the average amount of sleep that adults get per night with the average amount of sleep that:

(1) adults need per night.
(2) you get per night.
(3) you need per night.

In other words, how much sleep that adults actually get per night, on average, is not necessarily the amount that they need to get per night, on average. Furthermore, a group average tells us nothing specific about an individual member of that group. Thus, instead of referring to statistics and graphs, Moorcroft (1993) answered the question of how much sleep is needed by each person per night in this way:

Sleep as much as necessary so you do not feel tired the next day,”.... This is probably not the kind of answer you expected, but it is the best answer. While 7 1/2 hours per night is the average amount of sleep required for young adults [this claim is questionable: as just stated, this is the average amount that they get per night, not necessarily what they require], there are wide individual differences.... Some people do well with 6 hours or less per night, while others cannot live comfortably with less than 10 or 11 hours of sleep (Webb, 1975). Only you can determine how much sleep you require, since only you know when you feel good the next day. (p. 94)

So, go to sleep at a certain time each night for a few nights in a row and see what time you wake up in the morning (without an alarm clock). This is how much time you need for sleeping. For most of you, this will be between six and nine hours, but some of you will be outside of this range (see Figure 1). According to various reports, the least amount of sleep per night needed by a person was only one hour in the case of an elderly woman. Another person needed only three hours per night. But almost all of us need much more than this. If you need more than the average amount of sleep per night, try to arrange your daily schedule so that you can get this much sleep. Sleep involves a complex set of biological processes — processes that undoubtedly have some important functions. In fact, there is good evidence that, if you do not get enough sleep per night over long periods of time, there eventually will be a price to pay in terms of your health (Coren, 1996; GET NEW REFERENCES).

Figure 1. The Percentage of Adults Who Sleep From 3.5 to 10.5 Hours Per Night.
(from Moorcroft, 1993, p. 96)

What Are the Characteristics of Each Stage of Sleep?

In humans beyond the age of 5-6 months, there are five subdivisions, or stages, of sleep (Borbély, 1986; Dement, 1976; Lavie, 1996; Webb, 1975). When we first fall to sleep, we are in Stage 1. From there, we progress through Stage 2, Stage 3, Stage 4, and then, after about one hour, enter a stage known as Rapid-Eye-Movement (REM) sleep. Each stage has two major characteristics:

(a) a particular pattern of electrical activity in the brain;
(b) a particular cluster of mental and behavioral events.

We experience each of these five stages several times during the night. Just before you fall to sleep, your mind is relaxed and your thoughts drift, but your muscles still show a great deal of tension. Your EEG would show predominantly alpha waves at this time. This waking period just before sleep-onset is referred to as Stage 0 (zero is used because this period of relaxed wakefulness is not considered one of the five stages of sleep). You probably will spend about ten minutes or so in this stage before drifting into sleep. The point at which you first fall to sleep can be measured by sounding a soft tone and having you press a button each time the tone occurs. People who show brain activity suggesting that they are sleeping usually will stop pressing the button. You may go back and forth between Stage 0 and this stage of light sleep a few times before you stay asleep for good.

Stage 1—Light Sleep
At the onset of sleep, people show brain activity consisting of theta waves. During this stage, people can be awakened easily by quietly saying their names; and they often do not know that they are sleeping. When awakened, they may claim that they were just about to “fall to sleep.” Such subjective experiences suggest that Stage-1 sleep is a transitional stage between a waking state and a sleeping state. Stage 1 lasts about five minutes in young adults, on average.

As they enter Stage 1, people may have hypnagogic experiences, which are unusual perceptual experiences that occur when transitioning from a waking to a sleeping state. A common hypnagogic experience is a sinking feeling in the stomach (as if one were falling) coupled with jerking awake. Just before and during the muscle contractions, the person often experiences a vivid visual image. People are more likely to have such experiences when they are under stress or when they have changed their sleep schedules, but they can happen at other times as well. Hypnopompic experiences are unusual perceptual experiences that occur when transitioning from a waking to a sleeping state. When people are awakening, they may feel paralyzed (see this web site on sleep paralysis), feel a pressure on their chests, see or hear things that are not really there, and feel as if they are floating. These experiences can be very frightening and people may experience terror at these times. Hypnagogic and hypnopompic experiences may help to explain reports of ghosts and visitations of extraterrestrial beings (for example, Blackmore, 1998; Nickell, 1995; Reisner, 2001). It is not known why people have such experiences, but one possibility is that people are transitioning into or out of a dreams (see below).

Stage 2—Moderately Light Sleep
This stage is characterized by the appearance of "sleep spindles" and "K-complexes" (see Figure 2). A sleep-spindle is a rapid but short burst of electrical activity; a K-complex is a large fluctuation in voltage, which appears as a high peak and a deep valley on the EEG. Although it is some what more difficult to awaken people from Stage-2 sleep, about one-third of them still are not aware that they were sleeping. Delta waves also first appear during the second half of Stage-2 sleep, which shows that the cerebral cortex is becoming less active as sleep continues. Stage 2 generally lasts between 10 and 25 minutes, on average, in young adults.

Figure 2. Electrical activity as recorded by the EEG within the major stages of sleep
(from Groves & Rebec, 1992, p. 428)

Stage 3—Transitional Sleep
When delta waves make up at least 20% of EEG activity, people are said to be in Stage 3. As delta waves become more common (as the electrical activity in the cortex is reduced), people become much harder to awaken. The first episode of Stage 3 lasts about five minutes.

Stage 4—Deep Sleep
When delta waves make up at least 50% of EEG activity, people are said to be in Stage 4. Because delta waves are referred to as "slow waves," Stages 3 and 4 together are called slow-wave sleep (abbreviated as SW sleep). The first episode of Stage-4 sleep generally lasts about 20 to 40 minutes.

During SW sleep (especially during Stage 4), people sometimes experience “sleepwalking” and “sleep terrors.” Sleepwalking (also called somnambulism) is defined as the expression of complex movements during sleep — movements that indicate some sort of purposeful action. For example, when I was a teenager, a friend slept over at my house; and, during the night, he sat up, looked at me, and began moving his hand in the way that Bela Lugosi sometimes did in old movies when he was trying to hypnotize someone. A student once provided the example of her boyfriend, who sometimes got up during the night and made himself a breakfast of “pancakes,” consisting of dinner plates, and “syrup,” consisting of peanut butter which he spread over the plates. Sleepwalking is seen commonly in children (typically between the ages of about 4 and 10 years) but only rarely in adults.

The popular belief that it is dangerous to awaken a somnambulist (a “sleepwalker”) is false. In fact, it is much more dangerous not to awaken the person: he or she has little awareness of the physical surroundings and, thus, may get hurt. Furthermore, there are very rare occurrences in which a person may commit violent acts (including killing others) while sleepwalking. In this case, it might be dangerous to others not to awaken the sleepwalker (preferably from a safe distance).

A sleep (or night) terror is an abrupt awakening from SW sleep in which people (almost always children between about 4 and 10 years of age) feel and look terrified but often seem confused and are unable to supply a good reason for their terror. They may quickly go back to sleep and often are unaware of the event if asked about it the next morning. It seems that neither people who are sleepwalking nor people who are exhibiting sleep terrors typically are dreaming during the episode (see below), although they may report that they experienced an image or sound.

REM Sleep
At the end of Stage-4 sleep, there is a relatively rapid rise through stages 3 and 2 (which takes about 5-10 minutes) into a fifth stage of sleep called rapid-eye-movement (REM) sleep. You can observe this stage yourself by watching a sleeping-person’s eye movements about 60 minutes after they first go to sleep. When you see the eyes fluttering around in short bursts, the person is in REM sleep. The first episode of REM sleep lasts only about 1-5 minutes in young adults, on average.

The EEG activity observed during REM looks very similar to beta waves, which suggests that the brain is wide awake. Nevertheless, people are asleep during REM and, in fact, it may be very difficult to awaken them. In addition to the beta-like activity on the EEG, there are other interesting changes that occur during REM sleep:

(a) Physiological processes of the body (for example, blood pressure and heart rate) begin to look more like those of a person who is awake.
(b) Muscle tone decreases dramatically so that the person, in essence, becomes paralyzed.
(c) Genital arousal often occurs (that is, erections occur in males and labial swelling in females, along with concomitant[∂] signs of sexual arousal).
(d) Dreaming occurs frequently. In fact, when awakened during REM sleep, about 85% of people report that they were just dreaming.

During Stages 1-4 (referred to collectively as non-REM or NREM), fewer dreams are reported than during REM:

• Stage 1. About 50% of people report that they were just dreaming when awakened.
• Stage 2. About 10% of people report that they were just dreaming when awakened.
• Stage 3. There is little or no dreaming reported during this stage.
• Stage 4. There is little or no dreaming reported during this stage.

Sleep terrors may look like nightmares to an outside observer, but they are very different phenomena. A nightmare is a frightening dream that awakens a person. Sleep terrors, on the other hand, rarely or never are associated with dreams because they occur during SW sleep. Nightmares, by definition, are dreams and, hence, are most likely to occur during REM sleep and Stage-1 sleep. Later in this section, we will look more closely at dreaming.

Study Questions

1. What is the best way to figure out how much sleep you need per night?
2. Why are means of the amount of sleep people get per night not useful for determining how much sleep you need per night?
3. About how much sleep do adults get per night?
4. Should a person who needs only 4 hours of sleep per night be worried? Why or why not?
5. How are hypnagogic and hypnopompic experiences similar?
6. How do hypnagogic and hypnopompic experiences differ?
7. How do we know when a person is in each of the following stages of sleep?
   (a) Stage 1
   (b) Stage 2
   (c) Stage 3
   (d) Stage 4
   (e) NREM
   (f) REM
8. In which NREM stages are people most likely to dream?
9. Is a person dreaming during a sleep terror? Why or why not?
10. Is a person dreaming while sleepwalking? Why or why not?
11. Is a person dreaming during a nightmare? Why or why not?
12. What distinguishes REM sleep from NREM sleep?
13. Who is most likely to sleepwalk?
14. Who is most likely to experience a sleep terror?
15. During which stage or stages are people least likely to realize that they were just sleeping when they awaken?

What Changes In Sleep Are Observed During the Night?

During the night, we cycle several times through NREM and REM sleep stages. One cycle of sleep is shown in Figure 3:

Figure 3. One Cycle of Sleep.

The first sleep cycle of the night tends to last only about 60-75 minutes. Afterwards, each sleep cycle lasts about 90 minutes, on average. Because most adults sleep from seven to nine hours, we go through about five to six sleep cycles per night. As the night progresses, however, two major changes occur in the lengths of the stages making up each cycle:

(a) The duration of slow-wave sleep decreases in each successive cycle until Stages 3 and 4 eventually disappear during the second half of the night.
(b) The duration of REM sleep increases in each successive cycle, lasting only about 1-5 minutes during the first cycle, and about 40 minutes during the last cycle just before waking up.

Figure 4 illustrates these changes:

Figure 4. The Cycling of Sleep Stages During an Eight-hour Night in Young Adults.
(from Fernald, 1997, p. 166)

Individual Differences
The timing of the five stages as well as the characteristics of each stage differ among different people, and even over different nights for the same person. Some examples of such variations follow:

(1) People who are severely depressed are likely to quickly enter REM after first falling to sleep. This is called sleep-onset REM and is defined as entering REM after spending 20 minutes or less in Stages 1-4. Some people even enter REM as they fall asleep, thereby skipping Stages 1-4 altogether, especially if they have been deprived of sleep for some time.
(2) People who are taking sleeping pills or who have consumed too much alcohol show less REM sleep than others. In fact, if alcohol is abused over a long period of time, there may be such a severe reduction in REM sleep that the person feels fatigued and irritable much of the time.
(3) Some people may show a lack of muscle paralysis during REM sleep probably because the area of the brain that paralyzes the muscles is not functioning normally. When observed during REM sleep, these people often get up and begin performing many complex behaviors, as if they were acting out their dreams. Anch, Browman, Mitler, & Walsh (1988) described such a case:

A 54-year-old businessman and church leader has been complaining of mild dizziness and headaches for 7 days. At 3:30 a.m., his wife is awakened from a sound sleep by his mumbling long tirades of horrid profanities. The man then sits up in bed with his eyes open, but not seeming to be focused on anything in the room. He clumsily hits at his wife three times, striking her only once in the face. He then lies down and returns to peaceful sleep. Similar events occur again at 5:00 a.m. During the following day, he is surprised to hear of his nocturnal behavior and shows no impairment in his waking activity. However, he begins to exhibit profane vocalizations and violent actions 3-4 times each night, but remembers only occasional dreams and no conscious intention to curse or do violence. (p. 87)

Another man, who also would try to hit his wife while he was sleeping, was found to be dreaming about an argument with a coworker. Because these behaviors occur during REM sleep, we do not consider them to be examples of somnambulism (sleepwalking is defined as occurring during slow-wave sleep, not REM sleep).
(4) During afternoon naps, there are alterations of the timing of the five stages. For example, when napping, people enter REM more quickly and spend more time in it than they do at nighttime.
(5) The duration and timing of the five stages often change as a person ages. In the next section, some of the more common differences among age groups are described.

Study Questions

16. How would you define one cycle of sleep in your own words?
17. How many cycles of sleep would an adult go though if she slept a little over four hours during the night?
18. Are people more likely to have a nightmare during the first or the second half of the night?
19. Are people more likely to have a sleep terror during the first or the second half of the night?
20. Are people more likely to sleepwalk during the first or the second half of the night?
21. What happens to the amount of SW sleep as the night progresses?
22. What happens to the amount of NREM sleep as the night progresses? (Note: Before answering, please examine Figure 4.)
23. What happens to the amount of REM sleep as the night progresses?
24. What is "sleep-onset REM" and when is it most likely to occur?
25. Some people consistently use alcohol or sleeping pills to help them fall to sleep. Other than the possibility of addiction, why else may this not be a good idea?
26. What often happens when the large reduction of muscle tone characteristic of REM sleep does not occur?
27. What is a difference between afternoon naps and night-time sleeping in terms of the lengths of sleep stages?

How Does Sleep Change Over the Life Span?

From birth to old age, there are many changes in the general characteristics of sleep. Thus, the description provided above is correct only for a proportion of humans — those between about 20 and 40 years of age (and then, only for the average young adult). Other age groups differ in the patterning and timing of individual sleep stages, as well as in the total amount of time spent sleeping. Figure 5 illustrates average changes in REM and NREM sleep over the life span. Please keep in mind that this graph illustrates differences in the means of age groups. It ignores the broad range of differences among individuals within each age group.

Figure 5. Developmental Changes in the Proportions of REM and
NREM From Birth to 90 Years (from Peterson, 1997, p. 195)

Newborns
Newborns sleep about 16 hours per day, on average, with about six short sleep periods spread equally over 24 hours. During this early part of life, sleep is divided into only two stages: "active sleep" and "quiet sleep." When newborns first fall to sleep, they enter active sleep, during which they show a great deal of bodily activity (such as head movements, rapid eye-movements, fast and irregular respiration, and increased heart rate). Their EEG recordings show brain activity similar to that seen during REM sleep inf adults. Active sleep, therefore, seems to be the newborn infant’s version of REM sleep. After about 30 minutes of active sleep, newborns enter quiet sleep, a stage in which they show few movements except occasional jerks of their bodies that look to some as if they have just been frightened. Their EEG recordings show brain activity similar to a combination of the four stages of NREM sleep in adults. Quiet sleep, therefore, seems to be the newborn infant’s version of NREM sleep.

The sleep of newborns shows three major differences from the sleep of adults:

(a) The newborn cycles through the quiet and active stages about once every 60 minutes instead of the 90-minute cycles seen in adults.
(b) The newborn enters sleep by going into a REM-like stage instead of a NREM stage as in adults.
(c) The REM-like stage of active sleep makes up about 50 percent of each sleep period instead of the 20 percent seen in adults (see Figure 5).

It takes several years for the sleep of babies to develop into a pattern similar to that of adults.

Older Infants
Over the first year of life, the total amount of sleep per 24-hour period decreases to about 12-13 hours per day. In addition, the several periods of sleep in the newborn begin to combine into fewer and longer sleep periods until, by about six months of age, most sleep occurs during the night, with two much shorter periods of sleep occurring during the day. Within a few months after birth, characteristics of the separate NREM sleep stages begin to begin to emerge. As one example of this, sleep spindles, which define Stage 2 in older individuals, are first observed during the second month after birth, and continue to develop and become more distinct over the next several months.

Toddlers and Preschoolers
The amount and rate of change in the sleep stages that occurs from about 1 to 5 years of age varies widely from one individual to another, just as with any other physical or mental characteristic. Nevertheless, some average patterns can be described. Between 1 and 2 years of age, the four NREM sleep stages and REM sleep become fully distinct, although the duration of each differs from that described earlier for young adults. The total amount of sleep per 24-hour period declines from about 13 hours at 1 year to about 11 hours at 5 years of age. Most of this decrease occurs because of reductions in daytime napping (by 5 years, less than half of children take such naps regularly).

But perhaps the biggest change during this time occurs in the amount of REM sleep. At birth, active sleep makes up about 50% of the entire sleep period. But, by 2 years of age, REM sleep makes up only about 25-30% of sleep. Somewhere between 3 and 5 years of age, REM sleep decreases to only about 20% of the sleep period — a proportion that changes little after this time. That is, older children, adolescents, young adults, middle-aged adults, and elderly adults all spend about 20% of their sleep in the REM stagep. Nonetheless, you should keep in mind that, although the proportion of REM sleep does not change after about 3-5 years of age, the absolute amount of time spent in REM will decrease after this age because, as we age, we sleep fewer hours(see Figure 5 above).

Beginning sometime between 3 and 5 years of age, sleep disturbances — such as sleepwalking, nightmares, and sleep terrors — develop in many children. Although these disturbances often cause concern among parents, they usually decrease over time until, by late childhood, few children suffer frequently from them any longer. For example, probably all children between the ages of 3 and 5 years have nightmares at least occasionally, and many have frequent nightmares — nightmares that occur at least once per week (Hartmann, 1994).

Grade School Through Adolescence
Nightmares continue to be relatively frequent during grade school (6-11 years), but taper off throughout adolescence and into young adult (12-20 years). Probably about 50% of grade-school children have frequent nightmares, whereas only about 5% of late adolescents or young adults have frequent nightmares. The total amount of sleep decreases from about 10 hours per night at 6 years of age to about 8 hours per night at 17 years of age. In particular, the amount of deep sleep decreases dramatically beginning at about 12 years : there is about a 40% decrease from 12-17 years.

There is much evidence that adolescents tend to get less sleep than they need because many set their own bed times, which tend to be too late at night given that they still need to get up early in order to go to school (or engage in other activities). Thus, many adolescents show an increase in daytime napping in an attempt to make up for their sleep deficits.

PUT IN SOMETHING ABOUT CHANGES IN CIRCADIAN RHYTHM

Adulthood
There are enormous changes in the duration of particular stages of sleep beginning in early adulthood. Table 1 shows some of these changes by comparing the proportion of the total sleep period spent in each stage of sleep in very young adults and elderly adults:

Three major differences between the two age groups can be observed in Table 1:

(a) Stage 0. There is a large increase from early to late adulthood in the amount of time spent awake during the night.
(b) Stage 1. There is a large increase from early to late adulthood in the amount of time spent in light sleep.
(c) Stage 4. There is a large decrease from early to late adulthood in the amount of time spent in deep sleep.

In fact, by 60 years of age, many people no longer are getting any SW sleep (most likely to be observed in males). Older adults also tend to take more daytime naps than younger adults, presumably to make up for the reduced amounts of sleep obtained during the night. In general, the sleep of women changes less dramatically with age than does the sleep of men. Nevertheless, it is very difficult to generalize here because, during the later years of life, there is an increase in the amount of variance (average amount of individual differences) observed in sleep patterns.

There are some interesting changes in dreaming that occur in some people during adulthood. In late adulthood, people sometimes report that they dream less and recall fewer dreams than when they were younger. In fact, when an elderly person develops a progressive brain disease, such as Alzheimer's Disorder, the amount of REM sleep tends to decline dramatically (Montplaisir, Petit, Gauthier, Gaudreau, & Décary, 1998). About 50% of adults report that they never experience nightmares. On the other hand, nightmares sometimes become more frequent in older adults taking medicine for Parkinson’s disorder or hypertension, probably because of the effects of the medications on brain activity. In addition, adults who experience severely distressing events in their lives also report having more frequent nightmares. In rare instances, adults are lifelong sufferers of frequent nightmares, whether they are under stress or not, and whether they are taking medications or not. Surprisingly, the majority of such people report that they have no desire to end their frequent nightmares: they either make use of the nightmares (especially in artistic work) or feel as if the nightmares are an important part of who they are.

Study Questions

28. What are the main characteristics of the two stages of sleep in newborns, and how do they compare to the stages of REM and NREM sleep in adults?
29. In what ways do the onset of sleep and the timing of the sleep cycle differ between newborns and adults?
30. By about what age do children develop the five distinct stages of sleep observed in adults?
31. When during the life span do nightmares, sleepwalking, and sleep terrors first develop; and when are they usually no longer a problem?
32. At about what age does the percentage of REM sleep per night reach the level seen in adults?
33. At about what age do we observe the first large decrease in the amount of SW sleep obtained per night?
34. Which stages of sleep show the largest changes in duration from early to late adulthood? (Note: Please describe these changes in your answer.)
35. What do progressive brain diseases sometimes do to the amount of REM sleep obtained per night?

What Is Dreaming?

The mental activity that occurs during sleep does not always involve dreaming. Instead, at least some of this mental activity probably is similar to what we experience during the day when we are letting our minds wander: we experience relatively isolated thoughts and images that “drift by” in an unorganized manner. On the other hand, a dream consists of sequences of complex hallucinatory experiences occurring during sleep that (a) are accepted by the person as actual occurrences, and (b) change during a single episode. In other words, a dream is a progressing story made up of imagined sights and sounds that, at the time, are believed by the person to really be happening (Kramer, 1994; Jouvet, 1999). We know that dreaming occurs in humans most often during REM sleep, and that almost all mammals and many species of bird go into a stage similar to the REM sleep of humans. Does this mean that all these animals are dreaming? You may have noticed that dogs sometimes make barking or yelping noises and twitch their paws during sleep. When we see this happen, many of us say, “he’s dreaming about hunting!” Perhaps we infer this because we know that, when we dream, we seem to be talking and moving; and, therefore, we reason that a dog that barks and moves slightly during sleep also may be dreaming.

Nevertheless, it may be a case of overgeneralization[∂] to use human mental experiences during sleep to infer that dogs are having dream-like images when their paws twitch and they make noises during sleep. It could be that their movements and noises are merely reflex actions caused by the activation of particular brain structures during sleep. The only way we could know for certain whether an animal was dreaming would be to ask it. Of course, we cannot do this with dogs because they cannot answer our questions. On the other hand, some apes have been taught to use rudiments of language (by signing or pointing to pictures) to communicate with humans. One gorilla signed the phrase, “sleep pictures,” apparently in reference to the visual images seen during her dreams. If the structure in the brain (the pons) that paralyzes the body during REM sleep is surgically removed in cats, they often will move about their cages during REM sleep, apparently stalking and attacking objects in their dreams (perhaps hunting prey). Such examples suggest that other mammalian species dream (Jouvet, 1999).

It is very difficult to scientifically study dreams in humans because, in trying to be empirical — in attempting to observe directly the dream phenomena in which we are interested — it is possible that we may change the dreams that people have. Let's call this the observation effect, and define it as changes that occur in the phenomenon being studied when research participants know that they are being observed. If such an effect is influencing the results of a study, then our observations may not be telling us much about what actually happens out there in the “real world.” This is a potential problem in almost every study done in psychology because humans and many other animals often are aware that they are being observed. As researchers, we must always try to determine if the mere fact that participants are aware of being observed is having an effect on their behavior. In the case of dream research, some studies have shown that, in several important respects, dream reports gathered privately at home are not that different from those gathered in the laboratory. This suggests that studying dreams in sleep laboratories may not change very much their content and, hence, that dreams studied in laboratory research situations are similar enough to those occurring in natural circumstances (homes) to be useful in developing an testing theories about dreams and dreaming.

Some dream research has shown that there tends to be similarities in what people dream about from one night to the next, for at least short periods of time. One reason for this is the fact that our dreams often reflect the concerns and experiences we had during the previous days and weeks; and, to the extent that these issues are “on our minds,” we tend to dream about them. Sigmund Freud referred to the day-to-day concerns and experiences that make up our dreams as the day residue. People who experience emotionally intense events during their waking lives, for example, are likely to dream about them (or about related events) and to experience emotions consistent with these "dreamed-about" events. For instance, someone who has just experienced a divorce or the death of a family member may dream about losing something important (such as a diamond ring) and wake up feeling very sad. The concept of the "day residue" suggests that dreams can be meaningful because they reflect concerns, issues, problems, and experiences important to us in our everyday lives. On the other hand, it is unknown how much insight into our personalities we can gain by analyzing our dreams. Although Freud and other psychodynamic clinicians have claimed that dreams are uniquely useful for this purpose, the evidence supporting this claim is not strong. In fact, most of this evidence comes from case studies, which, as has already been discussed, suffer from some important weaknesses.

Dreams occur during REM and NREM sleep. Studies by several groups have shown that dreaming may occur as much as 50% of the time during the four NREM stages. Although this is less frequent than the 85% dreaming that occurs during REM sleep, it is still a quite significant amount of dreaming. What is surprising about the discovery that dreams occur in NREM (mostly Stages 1 and 2) is that, during the 1950s and 1960s, most sleep researchers claimed that dreaming occurred only during REM sleep. In fact, some of these early researchers still make this claim. For example, William Dement, a famous sleep researcher who began to study sleep when he was a graduate student in Nathaniel Kleitman's laboratory during the mid-1950s, recently argued that very few dreams occur during NREM (Dement, 1999). As evidence for this claim, he related the following anecdote[∂]: “In my early days with Nathaniel Kleitman, I often served as a research subject.... [I]n at least 100 awakenings from non-REM sleep, I never recalled dreaming” (p. 293). The fact that he didn't recall any dreams when awakened from NREM sleep is not good evidence that people, in general, don't dream during NREM: perhaps there is something unique about his sleep patterns. Furthermore, we don't know from which NREM stages he was awakened. If they were Stages 3 and 4, then it would not be surprising that he remembered no dreams: in general there is little or no dreaming during SW sleep.

Dement (1999) offered another anecdote as evidence for the claim that dreaming occurs primarily during REM sleep. In 1954, he quickly trained another medical student to identify REM tracings on an EEG. Dement then served as the subject so that he could show the other student the connection between REM sleep and dreaming. The student awakened Dement five times throughout the night, but Dement was completely unable to recall any dreams. By the fifth awakening, “I was so embarrassed and upset, I lied. I haltingly produced a phony dream fragment” (p. 293). It turned out, however, that the other student mistakenly had awakened Dement during periods of NREM, not REM sleep. Dement concluded that,“If anyone wants to claim that ... bias plays a role in the REM sleep-dreaming relationship, I could not have been more biased toward recalling a dream, and I was utterly unable to dredge up even a wisp of one” (p. 294). But again, anecdotes are not good evidence for or against a claim because they don't control for the effects of extraneous variables and are affected by the biases of the person retelling the anecdote.

When controlled research on dreaming is performed, researchers generally find that dreaming occurs during NREM rather frequently. Furthermore, they find that NREM dreams do not differ appreciably from REM dreams with respect to any characteristic (such as the vividness of the dreams; Rosenlicht & Feinberg, 1999). Thus, it seems that we must reject the equation of REM sleep with "dream sleep" — an equation claimed by many early sleep researchers. Instead, it seems that we can dream during any stage of sleep, although dreams occur most frequently during REM sleep, followed by light sleep (Stages 1 and 2). Very few people ever report dreaming when awakened from SW sleep (Stages 3 and 4). This suggests that high levels of brain activity typically are necessary for dreaming to occur.

In this vein, David Foulkes (1996, 1999) has argued that dreams are simply the workings of the conscious level whenever the brain is highly activeduring sleep. Foulkes (1999) stated that the “evidence suggests that dreaming is the form assumed by consciousness whenever there is residual ... [mind/brain] activation in the relative absence of direction either from the person’s environment or from voluntary self-control” (p. 2). In other words, Foulkes believes that we will dream whenever three conditions occur:

(a) our brains become activated;
(b) we are relatively unaware of the world outside of our bodies;
(c) we are unable to control the direction of our thoughts.

All three of these conditions occur during sleep, whether it involves NREM or REM brain activity. Thus, according to Foulkes and several other groups of researchers, dreaming can occur at anytime during sleep, although it is most common during REM sleep (perhaps because of the greater levels of brain activity that occur).

Study Questions

36. How would you define a "dream" in your own words?
37. When would a series of images and thoughts occurring during sleep NOT be an example of a dream?
38. What is some evidence that animals other than humans dream during sleep?
39. What happens during REM sleep in cats if part of the brain structure called the "pons" is removed in them?
40. What is meant by the term "observation effect" and why is it of concern to researchers who study human and animal behavior?
41. What is Freud's concept of the "day residue" and what does it suggest about the meanings of dreams?
42. What are the main problems with using anecdotes to support scientific claims?
43. During which stages of sleep do we dream the most?
44. According to David Foulkes, why do we dream so frequently during these stages?

What Causes Sleep?

Since the 1950s, sleep researchers have attempted to determine the main causes of sleep. Given the fact that every phenomenon is caused by a large number of interacting factors (multifactorial causation), it often helps to distinguish between proximal causes — those that occur closely in time to the phenomenon being explained — and distal causes — those that occur farther back in time. In the case of sleep, the proximal causes of greatest interest to researchers are brain structures and the chemicals that affect their electrical activity. The distal causes of greatest interest to researchers are the biological advantages of the stages of sleep that help individuals to survive longer and reproduce more, thereby leading to their evolution.

Proximal Causes of Sleep
The functioning of the brain certainly affects the functioning of the rest of the body; and the functioning of the rest of the body certainly affects the functioning of the brain. The brain affects the functioning of the rest of the body by generating electrical activity that travels through the spinal cord and, from there, to the rest of the nervous system. The spinal cord carries sensory information into your brain; and it also carries information from your brain out to the rest of the body. When the spinal cord enters the skull, it becomes a part of the brain called the brain stem. Electrical activity throughout the brain stem is very important for causing animals to fall to sleep and then to wake up again. For example, if we cut the brain stem of a cat where it connects to the spinal cord, the cat still shows normal sleep/wake patterns. On the other hand, if we cut the brain stem of a cat several inches above this point, the cat will appear to be permanently in SW sleep. Thus, the area between these two cuts must be important for producing the daily patterns of sleeping and waking. This area includes the part of the reticular activating system (RAS), which is a large area of the nervous system that begins in the spinal cord and travels through the brain stem and upward into the cerebral cortex (see Figure 6). Increasing activity in the RAS can wake up an animal, whereas decreasing activity may cause the animal to fall asleep. If you are daydreaming and a very loud noise occurs behind your head, you will immediately become highly alert. This is because the noise caused activity in the RAS which “woke up” the rest of the brain, especially the cerebral cortex. Activity within the pons seems to be important for initiating REM sleep.

Figure 6. The Reticular Activating System, Consisting of the Medulla and the Pons,
in the Brain Stem (image at Stanford University: HOPES Figure Index)

There are a number of chemicals produced in the brain that are important for inducing sleep. For example, if a brain chemical called "serotonin" is removed from a cat’s brain (by destroying neurons that produce this chemical), the cat will sleep very little or not at all for at least several days. Another chemical called "melatonin" seems to be important for making us feel sleepy. Darkness caused by the setting of the sun leads to increased melatonin production and increased sleepiness. Still other chemicals influence the onset of SW sleep and REM sleep. Abnormalities involving these chemicals may be important for the development of various sleep disorders. For example, insomnia (sleeping too little) may occur when there is too little melatonin in the brain, whereas increased activity of serotonin may be associated with hypersomnia (sleeping too much).

Distal Causes of Sleep
Almost all mammals and many birds show both REM and NREM sleep. The fact that this pattern of physiological activity occurs in many different species suggests that sleep and its separate stages have some very important functions — functions that first evolved in ancestral species shared by these modern animals. When we ask questions about the functions of sleep, we are concerned with what sleep does for us, with what its purpose is. When you get a good night’s sleep, your body and mind feel rested the next morning. On the other hand, when you don’t get a good night’s sleep, your body and mind do not feel rested. These findings suggest that one way to develop an adequate theory about the functions of sleep might be to deprive subjects of sleep and see what happens. Many researchers did this in the 1950s and 1960s, using both human and nonhuman animals. In total sleep-deprivation studies, participants are not allowed to sleep, typically for 2-3 nights in a row. In partial sleep-deprivation studies, on the other hand, the amount of sleep that participants are allowed per night is reduced, typically to only about 3-5 hours per night, sometimes for up to several months, but more often for only a week or two.

In general, total-sleep deprivation studies found that, when people are prevented from getting any sleep at all, they became very sleepy (they develop a strong desire to sleep), an unsurprising finding to say the least. In addition, participants in these studies experienced difficulties in concentrating on long and/or boring tasks (such as listening to a lecture), but often had little or no difficulty in concentrating on short and/or exciting tasks (such as playing a game requiring a lot of physical activity). These sleep-deprived participants tended to become uninterested in things that normally would interest them when they were well rested; and to make more mistakes on boring tasks, but not on exciting ones that could hold their attention. Nevertheless, in order to continue performing at normal levels, the bodies of sleep-deprived participants had to work much harder than normal. Therefore, they used more energy during total-sleep deprivation to perform tasks. Some total-deprivation studies showed that participants' physical fitness decreased the longer that they went without sleep. In addition, immune-system functioning decreased during prolonged sleep deprivation.

A commonly believed, but false claim is that people undergoing total-sleep deprivation for several days sometimes become psychotic — that they experience hallucinations and delusions. But, unless participants are taking stimulants (which can cause the development of psychotic symptoms) or already are predisposed to become psychotic, it does not seem to be true that short stretches of total-sleep deprivation will cause people to become psychotic. On the other hand, it can cause people to experience unusual perceptions (illusions). For example, an object such as a book may be mistaken for a cat, and the subject may even try to pet it. The difference between an illusiona and a hallucination is that a hallucination involves perceiving something that is not there, whereas an illusion involves misperceiving something that is there. Other psychological changes that also tend to occur with total-sleep deprivation are increased emotionality, irritability, and aggressiveness. In addition, many people begin to have problems with remembering events that have occurred recently.

What makes it so difficult to perform total sleep-deprivation studies is that people cannot stay awake after a day or two without sleep. The longest total sleep-deprivation study on record lasted for 11 days (Dement, 1999). This feat was accomplished in 1965 by a 17-year-old boy named Randy Gardner. However, Randy was unable to stay awake the entire time: after prolonged sleep deprivation, people enter brief periods of Stage-1 (light) sleep which are called microsleeps. During a microsleep, the person often appears to be awake and may even be engaged in some activity. In other animals, researchers can use more extreme methods to keep participants awake. For example, we are able to deprive subjects of sleep for much longer periods, although we can’t completely prevent short periods of light sleep. Studies performed by Allan Rechtschaffen and his colleagues involved placing rats on a disk that was floating in water (Rechtschaffen, Gilliland, Bergmann, & Winter, 1983). The disk was set up in such a way that, when the rat fell asleep, the disk would rotate, and the rat would have to begin walking in order to avoid falling in the water. In this way, the rat would get only about 10% of its normal sleep per day. When rats are sleep-deprived in this manner, they typically end up dying within two to four weeks. Some of the problems observed before death were weight loss (even with increased eating), sores on the paws and tail, increased expenditures of energy, and changes in hormone levels. Because a severe lack of sleep results in such problems — problems that lead eventually to the death of these animals — it is reasonable to conclude that sleep must have some very important biological functions associated with survival.

People who get less than their normal amount of sleep also exhibit some mild to moderate problems depending upon how much sleep they are getting and how long this deprivation lasts. The most consistent finding is that, when sleep is decreased to less than about six hours per night, people often report that they feel very sleepy, again a very unsurprising finding. There are, however, few consistent effects on the performance of partially sleep-deprived subjects on various kinds of tasks, however. Tasks that require a person to pay attention for longer periods of time are the ones most likely to show performance deficits after a couple of days of reduced sleep. Nevertheless, when sleep is reduced gradually over several months so that subjects get acclimated to less sleep, few or no effects are seen on performance measures, even though subjects continue to complain about fatigue. One interesting finding of long-term partial sleep-deprivation studies is that, when sleep was reduced to about five hours per night for about seven months, participants continued to sleep from one to almost three hours less per night after the study was completed compared to their previous sleep habits. The major problem with all of these studies, however, is that the measures used to look at the effects of sleep deprivation are limited to rough measures of performance and mood. They are not able to detect the more subtle physiological and psychological effects that may occur with prolonged sleep deprivation.

Thus, although many studies have attempted to discover the major functions of sleep, we still do not have good answers to this research question:

Like hunger or thirst, the drive for sleep appears to satisfy an elementary need. However, unlike eating and drinking, the purpose for sleep remains obscure. Sleep is the one major biological process whose raison d’être [reason for existing] has not yet been specified. Unraveling its essence constitutes a major challenge for biological research in general and for neuroscience in particular. (Borbély & Tononi, 1998, p. 167)

Several theories have been formulated over the years, but none have much evidence to support their claims.

Study Questions

45. Where is the reticular activating system and what does it do?
46. Which brainstem structures are important parts of the reticular activating system?
47. What do you think would happen with respect to REM sleep if you completely destroyed the pons in a cat?
48. What would happen to your sleep if your brain produced too little serotonin?
49. What would happen to your sleep if your brain produced too little melatonin?
50. Distinguish between total sleep-deprivation and partial sleep-deprivation studies?
51. What happens to humans who are kept awake for several nights in a row?
52. What happens to humans who sleep per night is reduced for one week to several months?
53. What happens to rats who are kept awake for weeks in a row?
54. What are the major functions of sleep?

Causes of REM Sleep
Because many sleep researchers, at least in the past, believed that almost all of our dreaming occurs during REM sleep, and because brain activity and physiological activityduring REM sleep look similar to the waking state, sleep researchers have been particularly interested in understanding this particular stage. Adults spend about one to two hours per night in REM sleep (which, if we live 75 years, equals over 40,000 hours of our lives — almost five years). Given that REM sleep takes up about 20% of the sleep period, it seems reasonable to infer that it has some some very important functions. Furthermore, much of the REM episode is spent dreaming. Is REM sleep important for biological reasons, psychological reasons, or both? In order to discover possible functions of REM sleep, some early work involved depriving people of REM sleep over several nights in order to see what would happen.

In selective sleep-deprivation studies, researchers deprive participants of either REM sleep or slow-wave sleep, while otherwise letting them get a full night’s sleep. It was predicted that, by depriving participants of a stage of sleep, the functions of that stage would be revealed in biological and/or psychological impairments. In this section, we are concerned with REM-deprivation studies, in which participants were awakened each time they entered REM sleep but otherwise were allowed to get a full night's sleep. Participants generally were deprived of REM sleep for 4-5 nights in a row. Researchers observed the following changes, on average:

(a) Participants entered REM more and more frequently the longer they were deprived of it.
(b) Participants felt unrested and often had difficulty concentrating during the day.
(c) When finally allowed to sleep undisturbed through the night, participants often exhibited a REM-rebound effect, in which the amount of REM showed a significant increase for 1-2 nights.

These psychological and behavioral changes suggested to researchers that REM sleep must have important functions: the body seems to work hard to make up for REM deficits. Nevertheless, as with total sleep-deprivation studies, no drastic changes were reported for any specific mental or physical process. For example, people deprived of REM for several nights in a row did not become psychotic.

Over the years, several theories have been developed that try to explain why we spend so much time in this stage. Nevertheless, there is little evidence in favor of any of them. Perhaps the most influential has been the activation-synthesis theory of J. Allan Hobson and Robert McCarley (Hobson, 1988). The activation-synthesis theory is based on the finding that, during REM sleep, the brain stem becomes very active — activity that “wakes up” large areas of the rest of the brain. Hobson and McCarley speculated that the brain needs to be activated several times during the night, perhaps to help in the development and maintenance of connections in the brain (for example, those connections that develop when we learn something new). They also believed (incorrectly, it seems) that dreaming occurs only during REM sleep. Thus, Hobson and McCarley explained dreams as being the result of the widespread brain activation that occurs during REM sleep: areas of the brain that are involved in seeing, hearing, and feeling the world become active due to activity in the brain stem. This activity, according to Hobson and McCarley, then causes us to “hallucinate” so that we think we are seeing, hearing, and feeling the outside world even though we are not. The problem with this idea, as we saw earlier, is that dreaming also occurs during NREM sleep. Thus, even if this theory is correct about the causes of REM dreaming (and there is little evidence at this point that it is), the theory still cannot explain the occurrence of dreams during NREM sleep when the brain is relatively inactive.

Another theory of dreaming that was very influential in psychiatry, psychology, and the wider American culture during much of the twentieth century was developed by Sigmund Freud. From about 1895 until his death, Freud developed a set of ideas and therapeutic practices known as psychoanalysis — an approach that assumed that human behaviors, thoughts, and emotions are caused by unconscious conflicts among competing motivations. Freud wanted to understand the development of personality in individuals, especially the development of abnormalities in personality. He believed that everything we did was the outcome of varioust desires and wishes (motives) in conflict with one another. For example, I would bet that, right now, you are experiencing conflicting desires: a part of you wants to read this section carefully so that you can understand it better, and another part of you would like to be doing something else that is more fun. You are experiencing conflict. The outcome of this conflict will be different for each of you, however. Some of you will race through this section so that you can put the book down and do the other thing you desire. Some of you will force yourselves to concentrate on the material anyway and continue to read it carefully. Others of you have already put the book down and, so, are no longer reading this. And still others of you never picked the book up in the first place, and don’t ever plan to. So, out of this identical conflict, different behaviors, emotions, and thoughts arise in each person. These individual differences in how conflicts are resolved indicate personality differences.

For Freud, the most important conflicts between motives occur at the unconscious level. These are conflicts of which we do not want to be aware because we are trying to forget them: they upset us too much. Therefore, according to Freud, we push them into the unconscious level where they can remain hidden from our awareness (a process is known as “repression”). For example, Freud claimed that all of us, beginning at about the age of three years or so, develop sexual feelings for our opposite-sexed parent (boys for their mothers and girls for their fathers) and aggressive feelings for our same-sexed parent (boys for their fathers and girls for their mothers). He called this the “Oedipus Complex.” These feelings, he said, come into conflict with other motives, such as our desire to be loved by the parent towards whom we are feeling aggressive. Furthermore, we eventually become aware of societal standards of behavior that prohibit such feelings towards our parents. We become very distressed about experiencing these desires. Thus, Freud claimed that, by about six years of age, we repress this conflict by pushing it into our unconscious. In this way, we become unaware of our oedipal desires, which means that they no longer can upset us.

What do such unconscious conflicts have to do with dreaming? Freud argued that a major function of dreams is “wish fulfillment”: he believed that dreams allow us to partially satisfy our illicit (secret and forbidden) desires through fantasy. When you are awake, you sometimes fantasize because it can be fun: these waking fantasies can satisfy to some extent a conscious wish or desire. For example, you may daydream about being a rich and famous person, and this daydream will satisfy the desire to some extent. For Freud, dreams were fantasies of this kind — dreams partially satisfy unconscious wishes and desires. The problem, however, is that even during sleep we don’t want to be completely aware of our unconscious desires because they still upset us. Thus, when we dream, Freud said, we don’t dream directly about the repressed desires. Instead, we dream about something that symbolizes these desires for us — we transform the repressed desire into something else that represents the desirecin a way that, at the conscious level, we won't recognize. For example, if a man’s dream involves his oedipal desires to have sex with his mother, he will not dream about this directly. Instead, he might dream about going out on a date with his third-grade teacher from forty years before and getting into a fight with the principal (symbolizing his father) who was dining at the same restaurant. In this manner, according to Freud, the man can satisfy to a small extent his repressed motives while remaining unaware that he is doing so. Freud explained the existence of nightmares as dreams in which we are in danger of becoming aware of our repressed desires. As the actual desire threatens to break into conscious awareness, we become terrified and wake up.

In his theory of dreaming, Freud distinguished two levels of the dream:

(a) The latent content of the dream is the set of unconscious motives (desires) that are expressed in symbolic form in the dream. The word “latent” means “hidden.” In other words, the latent content is the set of unconscious desires that represents the the true meaning of the dream. In the example, the man actually is dreaming about his oedipal desires for his parents even though he doesn’t know it.
(b) The manifest content of a dream is the actual narrative (story line) of a dream — it is what you tell another person when you describe the dream you had. The word “manifest” means “what is expressed directly." In the example, the man dreamed about taking his third-grade teacher on a date and getting into a fight with his principal.

In therapy, Freud listened to the manifest content of his patients' dreams, and then interpreted them in terms of their latent content. By interpreting “what was expressed ” in terms of “what was hidden,” Freud tried to make his patients aware of the unconscious desires that he believed were motivating the patient’s abnormal behaviors when awake.

Is Freud’s theory of dreaming a good one? Over the years, it has been criticized severely by many psychologists, psychiatrists, and others. Its biggest problem is that much of the research designed to test the theory does not support it. What sorts of predictions are implied by Freud’s theory? One possibility is that, if Freud's theory is true, people should dream more when their unconscious conflicts are activated. For example, with regard to the Oedipal Complex, perhaps people will dream more when a parent dies, or when their parents divorce, or when the people are about to get married, and so on. But we find that these predicted observations don’t occur. It seems that people dream about the same amount each and every night: about 85% of the time in REM, about 50% of the time in Stage 1, and about 10% of the time in Stage 2. Probably the biggest problem with Freud’s theory is that it is just too difficult to test: we have no direct access to the unconscious desires that are thought to be the wellsprings of the dream. Thus, although variants of Freud’s theory of dreaming are still very popular among many therapists, most scientific researchers studying dreaming find his theory to be of historical interest only.

Study Questions

55. What is a selective sleep-deprivation study?
56. What is a REM-deprivation study?
57. What happens to people who are selectively deprived of REM sleep for several nights in a row?
58. What happens to REM-deprived subjects when they finally are allowed to sleep undisturbed?
59. What is the main claim of the activation-synthesis theory of REM sleep?
60. What are the most important difficulties for the activation-synthesis theory of REM sleep?
61. What is the main claim of the psychoanalytic theory of dreaming?
62. What are the most important difficulties for the psychoanalytic theory of dreaming?

ADD:
1. COGNITION & DREAMS: Bootzin, R. R., Kihlstrom, J. F., & Schacter, D. L. (1990).
2. MEMORY CONSOLIDATION & DREAMS