Sleep, Dreaming, and Circadian Rhythms - Biopsychology Global Edition 11th Ed PDF

Chapter 14 Sleep, Dreaming, and Circadian Rhythms How Much Do You Need to Sleep? fizkes/Shutterstock Chapter Overview and Learning Objectives Stages of Sleep LO 14.1 Describe the...

Chapter 14 Sleep, Dreaming, and Circadian Rhythms How Much Do You Need to Sleep? fizkes/Shutterstock Chapter Overview and Learning Objectives Stages of Sleep LO 14.1 Describe the three standard physiological measures of sleep. LO 14.2 Describe the three stages of the sleep EEG and explain the difference between REM and non-REM sleep. Dreaming LO 14.3 Describe the discovery of the relationship between REM sleep and dreaming. LO 14.4 Describe five common beliefs about dreaming and assess their validity. LO 14.5 Understand the relationship between REM sleep, NREM sleep, and dreaming. LO 14.6 Define lucid dreaming and discuss the research that supports its existence. 371 M14_PINE1933_11_GE_C14.indd 371 22/01/2021 15:27  372 Chapter 14 LO 14.7 Discuss the issue associated with studying dream content and describe findings related to what can influence dream content. LO 14.8 Compare and contrast three different theories of why we dream. LO 14.9 Identify three brain areas that have been implicated in dreaming. Why Do We Sleep, and LO 14.10 Describe the two kinds of theories of sleep. Why Do We Sleep When LO 14.11 Explain four conclusions that have resulted from the We Do? comparative analysis of sleep. Effects of Sleep Deprivation LO 14.12 Explain how stress can often be a confounding variable when considering the effects of sleep deprivation. LO 14.13 List the three predictions that recuperation theories make about the effects of sleep deprivation. LO 14.14 Describe two classic sleep-deprivation case studies. LO 14.15 Describe the major effects of sleep deprivation in humans. LO 14.16 Describe the key studies of sleep deprivation in laboratory animals. Provide a critique of the carousel apparatus as a method of sleep deprivation. LO 14.17 Describe the effects of REM-sleep deprivation. LO 14.18 Describe six pieces of evidence that indicate that less sleep is associated with more efficient sleep. Circadian Sleep Cycles LO 14.19 Describe the circadian sleep–wake cycle and the role of zeitgebers in maintaining circadian rhythms. LO 14.20 Describe free-running rhythms and internal desynchronization and explain why they are incompatible with recuperation theories of sleep. LO 14.21 Describe the disruptive effects of jet lag and shift work on circadian rhythmicity and how one can minimize such effects. LO 14.22 Describe the research that led to the discovery of a circadian clock in the suprachiasmatic nucleus (SCN) of the hypothalamus. LO 14.23 Explain the mechanism by which SCN neurons are entrained by the 24-hour light–dark cycles. LO 14.24 Understand the genetics of circadian rhythms and the important discoveries that have resulted from the discovery of circadian genes. Four Areas of the Brain LO 14.25 Describe the research that led to the identification of the anterior Involved in Sleep and posterior hypothalamus as brain regions involved in the regulation of sleep and wakefulness. M14_PINE1933_11_GE_C14.indd 372 22/01/2021 15:27  Sleep, Dreaming, and Circadian Rhythms 373 LO 14.26 Describe the research that led to the identification of the reticular formation as a brain region involved in the regulation of sleep and wakefulness. LO 14.27 Discuss how REM sleep is controlled by the reticular formation and what implications this has for understanding the neural mechanisms of behavior. Drugs That Affect Sleep LO 14.28 Describe three classes of hypnotic drugs. Compare and contrast them in terms of their efficacy and side effects. LO 14.29 Describe three classes of antihypnotic drugs. LO 14.30 Understand the relationship between the pineal gland and melatonin, and how melatonin affects sleep. Sleep Disorders LO 14.31 Describe four causes of insomnia. LO 14.32 Describe the symptoms of narcolepsy and the role of orexin (hypocretin) in this disorder. LO 14.33 Describe one REM-sleep-related disorder and its presumed neural mechanisms. Effects of Long-Term Sleep LO 14.34 List the main differences between short and long sleepers. Reduction LO 14.35 Describe the results of studies of long-term reduction of nightly sleep. LO 14.36 Describe the results of studies of long-term reduction of sleep by napping. LO 14.37 Recognize how shorter sleep times relate to longevity. Most of us have a fondness for eating and sex—the can comfortably get—the usual prescription being at least two highly esteemed motivated behaviors discussed in 8 hours per night. The other answer is that many of us sleep Chapters 12 and 13. But the amount of time devoted to these more than we need to and are consequently sleeping part behaviors by even the most amorous gourmands pales in of our life away. Just think how your life could change if comparison to the amount of time spent sleeping: Most of us you slept 5 hours per night instead of 8. You would have an will sleep for well over 175,000 hours in our lifetimes. This extra 21 waking hours each week, a mind-boggling 10,952 extraordinary commitment of time implies that sleep fulfills hours each decade. a critical biological function. But what is it? And what about As we prepared to write this chapter, I (JP) began to think dreaming: Why do we spend so much time dreaming? And of the personal implications of the idea that we get more why do we tend to get sleepy at about the same time every sleep than we need. That is when I decided to do something day? Answers to these questions await you in this chapter. a bit unconventional. I am going to try to get no more than Almost every time we lecture about sleep, somebody 5 hours of sleep per night—11:00 p.m. to 4:00 a.m.—until this asks, “How much sleep do we need?” Each time, we pro- chapter is written. As I begin, I am excited by the prospect of vide the same unsatisfying answer: We explain that there are having more time to write, but a little worried that this extra two fundamentally different answers to this question, but time might cost me too dearly. neither has emerged as a clear winner. One answer stresses It is now the next day—4:50 Saturday morning, to be the presumed health-promoting and recuperative powers of exact—and I am just sitting down to write. There was a sleep and suggests that people need as much sleep as they party last night, and I didn’t make it to bed by 11:00; but M14_PINE1933_11_GE_C14.indd 373 22/01/2021 15:27  374 Chapter 14 considering that I slept for only 2 hours and 15 minutes, Figure 14.1 A participant in a sleep experiment. 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 (Meddis, 1977). Ponder its implications before proceeding to the body of the chapter. The Case of the Woman Who Wouldn’t Sleep Miss M. usually sleeps only 1 hour per night. Although she is retired, she keeps busy painting, writing, and volunteering in the community. Although she becomes tired physically, she never reports feeling sleepy. During the night she sits on her bed read- ing, writing, crocheting, or painting. At about 2:00 a.m., she Hank Morgan/Science Source often falls asleep without any preceding drowsiness, and when she wakes about 1 hour later, she feels wide awake. muscles during these same sleep periods. Subsequently, She came to the laboratory for some sleep tests, but on the electroencephalogram (EEG), the electrooculogram the first night we ran into a snag. She told us she did not sleep (EOG), and the neck electromyogram (EMG) became the at all if she had interesting things to do, and she found her visit to a sleep laboratory very interesting. She had someone to talk three standard psychophysiological bases for defining the to for the whole night. stages of sleep. In the morning, we broke into shifts so that some could Figure 14.1 depicts a volunteer participating in a sleep sleep while at least one person stayed with her. The second experiment. A participant’s first night of sleep in a laboratory night was the same as the first. is often fitful. That’s why the usual practice is to have each Finally, on the third night, she promised to try to sleep, and participant sleep several nights in the laboratory before com- she did. The only abnormal thing about her sleep was that it was mencing a sleep study. The disturbance of sleep observed brief. After 99 minutes, she could sleep no more. 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- Stages of Sleep related, rather than a sex-related, phenomenon. Many changes occur in your body during sleep. This mod- ule introduces you to three standard measures of those Three Stages of Sleep EEG physiological changes, and how they change over the LO 14.2 Describe the three stages of the sleep EEG and course of a night’s sleep. explain the difference between REM and non- REM sleep. Three Standard Psychophysiological According to the American Academy of Sleep Medicine, Measures of Sleep there are three stages of sleep EEG: stage 1, stage 2, and stage 3 (see Grigg-Damberger, 2012). Examples of these LO 14.1 Describe the three standard physiological three stages are presented in Figure 14.2. measures of sleep. After the eyes are shut and a person prepares to go to There are major changes in the human EEG during the sleep, alpha waves—waxing and waning bursts of 8- to course of a night’s sleep. Although the EEG waves that 12-Hz EEG waves—begin to punctuate the low-voltage, accompany sleep are generally high-voltage and slow, high-frequency waves of alert wakefulness. Then, as the there are periods throughout the night that are dominated person falls asleep, there is a sudden transition to a period by low-voltage, fast waves similar to those in nonsleeping of stage 1 sleep EEG. The stage 1 sleep EEG is a low-voltage, individuals. In the 1950s, it was discovered that rapid high-frequency signal that is similar to, but slower than, eye movements (REMs) occur under the closed eyelids of that of alert wakefulness. sleepers during these periods of low-voltage, fast EEG There is a gradual increase in EEG voltage and a decrease activity. And in 1962, Berger and Oswald discovered that in EEG frequency as the person progresses from stage 1 sleep there is also a loss of electromyographic activity in the neck through stages 2 and 3. Accordingly, the stage 2 sleep EEG M14_PINE1933_11_GE_C14.indd 374 22/01/2021 15:27  Sleep, Dreaming, and Circadian Rhythms 375 has a slightly higher amplitude and a Figure 14.3 The course of EEG stages during a typical night’s sleep and the lower frequency than the stage 1 EEG; relation of emergent stage 1 EEG to REMs and lack of tone in core muscles. in addition, it is punctuated by two characteristic wave forms: K complexes and sleep spindles. Each K complex is Awake a single large negative wave (upward Sleep EEG deflection) followed immediately by a Stage 1 single large positive wave (downward Stage 2 deflection)—see Mak-McCully and colleagues (2014). Each sleep spindle Stage 3 is a 0.5- to 2-second waxing and wan- ing burst of 11- to 15-Hz waves (see 0 1 2 3 4 5 6 7 8 9 Purcell et al., 2017). The stage 3 sleep Hours EEG is defined by a predominance of Periods of REM Lack of core-muscle tone delta waves—the largest and slowest EEG waves, with a frequency of 1 to 2 Hz. Once sleepers reach stage 3 EEG sleep, they stay there for a time, and then they retreat back stage 1 EEG) are accompanied by rapid eye movements through the stages of sleep to stage 1. However, when they (REMs) and by a loss of tone in the muscles of the body core. return to stage 1, things are not at all the same as they were After the first cycle of sleep EEG—from initial stage 1 to the first time through. The first period of stage 1 EEG during stage 3 and back to emergent stage 1—the rest of the night is a night’s sleep (initial stage 1 EEG) is not marked by any spent going back and forth through the stages. Figure 14.3 striking electromyographic or electrooculographic changes, illustrates the EEG cycles of a typical night’s sleep and the whereas subsequent periods of stage 1 sleep EEG (emergent close relationship between emergent stage 1 sleep, REMs, and the loss of tone in core muscles. Notice that each cycle tends to be about Figure 14.2 The EEG of alert wakefulness, the EEG that precedes sleep onset, 90 minutes long and that, as the night and the three stages of sleep EEG. Each trace is about 10 seconds long. progresses, more and more time is spent in emergent stage 1 sleep, and less and Alert wakefulness less time is spent in the other stages, par- ticularly stage 3. Notice also that there are brief periods during the night when Just before sleep the person is awake, although he or she usually does not remember these periods of wakefulness in the morning. Alpha waves Let’s pause here to get some sleep-stage terms straight. The sleep Stage 1 associated with emergent stage 1 EEG is often called REM sleep (pronounced “rehm”), after the associated rapid eye movements; whereas all other stages of sleep together are called NREM sleep Stage 2 (non-REM sleep). Accordingly, initial stage 1, stage 2, and stage 3 sleep are sometimes referred to as NREM 1, Sleep spindle K complex NREM 2, and NREM 3, respectively (see Grigg-Damberger, 2012). NREM 3 is often Stage 3 referred to as slow-wave sleep (SWS), after the delta waves that characterize it. Table 14.1 summarizes the various sleep- stage terms. REMs, loss of core-muscle tone, and a low-amplitude, high-frequency EEG are not the only physiological correlates M14_PINE1933_11_GE_C14.indd 375 22/01/2021 15:27  376 Chapter 14 of REM sleep. Cerebral activity (e.g., oxygen consumption, an opportunity to test some common beliefs about dream- blood flow, and neural firing) increases to waking levels in ing. The following five beliefs were among the first to be many brain structures, and there is a general increase in the addressed. variability of autonomic nervous system activity (e.g., in EXTERNAL STIMULI AND DREAMS. Many people blood pressure, pulse, and respiration). Also, the muscles believe that external stimuli can become incorporated into of the extremities occasionally twitch, and there is almost their dreams. Dement and Wolpert (1958) sprayed water on always some degree of penile or clitoral erection. sleeping volunteers after they had been in REM sleep for a few minutes and then awakened them a few seconds later. Table 14.1 Summary of Various Sleep-Stage Terms In 14 of 33 cases, the water was incorporated into the dream report. The following narrative was reported by one partici- REM sleep Emergent stage 1 EEG pant who had been dreaming that he was acting in a play: NREM sleep Initial stage 1 EEG (NREM 1) I was walking behind the leading lady when she suddenly Stage 2 EEG (NREM 2) collapsed and water was dripping on her. I ran over to her Stage 3 EEG (NREM 3) and water was dripping on my back and head. The roof Slow-wave sleep Stage 3 EEG (NREM 3) 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. (Dement, W. C., & Wolpert, E. A. (1958)) Dreaming We now know that some external stimuli are more Of all the topics I (SB) teach, few inspire more discussion likely to be incorporated into a dream than others (see in class than the topic of dreaming. This is in part because Broughton, 1982; Schredl et al., 2009). Water droplets hap- people have so many beliefs and theories about dreaming. pen to be one of those. The stimulus that is most readily A major goal of this module is to assess those beliefs and incorporated into a dream is the feeling of pressure on a explore current theories and research related to dreaming. limb (see Schredl et al., 2009). DREAM DURATION. Some people believe dreams last Discovery of the Relationship only an instant, but early research on the topic suggested between REM Sleep and Dreaming that dreams run in “real time.” In one study (Dement & Kleitman, 1957), participants were awakened 5 or 15 min- LO 14.3 Describe the discovery of the relationship utes after the beginning of a REM episode and asked to between REM sleep and dreaming. decide on the basis of the duration of the events in their Nathaniel Kleitman’s laboratory was an exciting place in dreams whether they had been dreaming for 5 or 15 min- 1953. REM sleep had just been discovered, and Kleitman utes. They were correct in 92 of 111 cases. and his students were driven by the fascinating implication Current research on dream duration supports the notion of the discovery. With the exception of the loss of tone in that dreams run slightly slower than real time. For example, the core muscles, all of the other measures suggested that physical movement while in a dream can take up to 40% REM sleep episodes were emotion-charged. Could REM longer than in a waking state (see Erlacher et al., 2014). sleep be the physiological correlate of dreaming? Support PEOPLE WHO DON’T DREAM. Some people claim that for the theory that REM sleep is the physiological correlate they do not dream. However, studies conducted in the of dreaming came from the observation that 80 percent of 1950s showed that these people have just as much REM awakenings from REM sleep, but only 7 percent of awak- sleep as normal dreamers: Most reported dreams if they enings from NREM sleep, led to dream recall. The dreams were awoken during REM episodes (see Goodenough recalled from NREM sleep tended to be isolated experiences et al., 1959), although they did so less frequently than did (e.g., “I was falling”), while those associated with REM normal dreamers. The results of more recent studies are sleep tended to take the form of stories, or narratives. mixed: Some studies have found these individuals do not appear to dream (e.g., Pagel, 2003), whereas others are more Testing Common Beliefs About consistent with the earlier findings (e.g., Herlin et al., 2015). Dreaming SEXUAL CONTENT IN DREAMS. Penile erections are commonly assumed to be indicative of dreams with sexual LO 14.4 Describe five common beliefs about dreaming content. However, erections are no more complete during and assess their validity. dreams with frank sexual content than during those with- The relationship between REM sleep and dream recall that out it (Karacan et al., 1966). Even babies have REM-related Kleitman and colleagues discovered provided them with penile erections (see Fanni et al., 2018). M14_PINE1933_11_GE_C14.indd 376 22/01/2021 15:27  Sleep, Dreaming, and Circadian Rhythms 377 SLEEPTALKING AND SLEEPWALKING. Many people watching a film that I know quite well. The person to the right of believe sleeptalking (somniloquy) and sleepwalking me starts talking loudly to the person on my left, arguing over (somnambulism) occur during REM sleep and are therefore the title of the film. associated with dreaming. This is not so (see Alfonsi et al., “It’s Ferris Bueller’s Day Off.” “No, you idiot, it’s The Breakfast Club,” says the one on 2019). Sleeptalking has no special association with REM my left. sleep—it can occur during any stage but often occurs during “Like you know anything about films,” says the one on my the transition to wakefulness. Sleepwalking usually occurs right, voice rising further. during slow-wave sleep, and it never occurs during REM “More than you ever will,” yells the other. sleep, when core muscles tend to be totally relaxed (see Meanwhile I am stuck in the center of this escalating argu- Castelnovo et al., 2018; Januszko et al., 2015). ment, trying my best to enjoy the film and growing increasingly frustrated to the point of yelling “shut up!” Does REM Sleep = Dreaming? Then I often wake up. Not infrequently, I wake up on a bus: turning bright red with the realization that I had just told LO 14.5 Understand the relationship between REM the whole bus to shut up; the other riders looking quite amused sleep, NREM sleep, and dreaming. by my embarrassment. Then, one night I had that same dream. But something While there are still adherents to the theory that REM sleep was different this time. When the argument began as usual, and dreaming can be equated, the situation has been com- I suddenly realized I was in a dream and decided to take control plicated by three key discoveries. First, it is now well estab- of things. I slowly levitated up from my seat. Then, floating high lished that dreaming occurs during NREM sleep (see Siclari above my two nemeses, I smirked, leaned back, and enjoyed & Tononi, 2017). Second, the qualities of many NREM the film. dreams are comparable to REM dreams (see McNamara et al., 2010). This is especially true for NREM dreams that occur later in the night: They are hallucinatory and have a For a long time, sleep researchers believed it was storyline, just like REM dreams (see Siclari & Tononi, 2017). impossible to have a lucid dream (see Baird, Mota-Rolim, Finally, REM sleep and dreaming can be dissociated (see & Dresler, 2019). In the 1980s, LaBerge conducted a series Siegel, 2011). For example, antidepressants greatly reduce of studies that left little doubt that lucid dreaming was a or abolish REM sleep without affecting aspects of dream real phenomenon (see Schredl, 2018). Indeed, previous sur- recall (see Oudiette et al., 2012). Conversely, specific cortical veys had indicated that many people have at least one lucid lesions can abolish dreaming without affecting REM sleep dream during their lives; some have them regularly; and a (see Nir & Tononi, 2010). select few have them every night (see Ribeiro, Gounden, & Quaglino, 2016; Saunders et al., 2016). Lucid Dreaming LaBerge’s technique for demonstrating lucid dream- ing in his studies involved having self-proclaimed lucid LO 14.6 Define lucid dreaming and discuss the dreamers sleep in his laboratory. Before allowing them to research that supports its existence. fall asleep, LaBerge would instruct them to carry out a spe- Have you ever been aware that you are dreaming? If so, have cific bodily movement (e.g., repeated left-right-left-right you ever taken control of your dream and made it unfold as eye movements while in their dream when given a specific you so desire? Lucid dreaming is the ability to be consciously signal, such as flashes of light on their eyelids; see Baird, aware that one is dreaming and, in some cases, be able to Mota-Rolim, & Dresler, 2019; LaBerge, Baird, & Zimbardo, control the content of one’s dream (see LaBerge, LaMarca, 2018). The following case study is an example of such a pro- & Baird, 2018; Ribeiro, Gounden, & Quaglino, 2016). Think cedure, and it illustrates just how much control some lucid of the joy of being able to control one’s dream. Want to have dreamers have over their dreams. great sex? Want to be a superhero? Want to travel to the International Space Station? Having a lucid dream allows The Case of the Artistic Dreamer you to take control of your dream and do any of these things. I (SB) experience lucid dreams from time to time. A sleep researcher was at a dinner party with a large group. The topic of dreaming came up during the meal, and one of the guests, M.S., claimed that they always had lucid dreams. The The Case of the Levitating sleep researcher was skeptical. She decided to put M.S.’s claim Teenager to the test. She invited M.S. to sleep a few nights in her sleep lab. When M.S. arrived, she sat them down on the bed, attached It was a recurring dream that plagued me (SB) as a teenager: EEG electrodes to their scalp, attached EOG electrodes around I am in an otherwise empty movie theatre, apart from myself and their eyes, attached some EMG electrodes to their arm, and two other individuals, one seated on either side of me. We are then asked them to lie down. M14_PINE1933_11_GE_C14.indd 377 22/01/2021 15:27  378 Chapter 14 The sleep researcher gave M.S. the following instructions: “Careful what you wish for,” G.D. said from her usual spot “When you see a flashing light in your dream use your right arm in the back row of the classroom. It was towards the end of the to draw a star.” term and it was the first time that she had spoken. M.S. chuckled: “You could at least give me something “What do you mean?” I asked. interesting to draw.” Then they fell asleep. “I lucid dream every night,” G.D. said. “I have as long as The sleep researcher watched and waited for M.S. to enter I can remember. I only rarely have non-lucid dreams and they REM sleep. After an hour and a half, M.S. was showing the are wonderful when I do.” signs: Their EEG was low amplitude and high frequency, and “How so?” I said in a tone dripping with puzzlement. they were displaying rapid eye movements. The researcher took “Imagine you knew the entire plot line of a movie before you her flashlight and pointed it at M.S.’s eyes. She rapidly switched begin watch it. Now, imagine if that were true for every movie the flashlight off and on, watching the EMG carefully as she did you ever watched.” so. What she saw next made her believe in lucid dreams: M.S.’s “I get it. If you always lucid dream it’s like always knowing arm muscles, in the absence of overt movement, displayed a how your dream will unfold.” series of contractions identical to what you would see if some- “Yep! For me, lucid dreaming is about as boring as a one were drawing a star. lecture,” said G.D. The class chuckled. I turned bright red. Most students get excited about the prospect of lucid dreaming. I am often asked how one might become a lucid Another reason lucid dreams might be considered dreamer (see Aviram & Soffer-Dudek, 2018). There are sev- boring is that they tend to be less bizarre than nonlucid eral methods that have been shown to increase the likeli- dreams (see Yu & Shen, 2020). Also, concerns have been hood that one will have a lucid dream (see Bazzari, 2018). raised that lucid dreaming might have a negative impact Some examples include transcranial electrical stimulation on sleep quality (see Soffer-Dudek, 2020; but see Schredl, (see Chapter 5) applied to the frontal and temporal areas Dyck, & Kühnel, 2020). of the skull (see Bray, 2014; Voss et al., 2014), certain cog- Lucid dreamers have been a boon to sleep researchers. nitive training techniques (see LaBerge, LaMarca, & Baird, Because they are aware in their dreams and are better able 2018), and the administration of acetylcholine agonists (see to recall their dreams when they awaken (see Aspy et al., LaBerge, LaMarca, & Baird, 2018). 2017), they are particularly well equipped to describe the Don’t worry. We have not forgotten you. We know sensory qualities of their dreams. Two examples: that many of you were hoping that you might get some pointers in this module on how you might experience lucid Lucid dreamers report that gustatory, olfactory, and dreaming yourself, and we also know that you are unlikely somatosensory stimuli are uncommon in their dreams to have your own brain stimulator or stash of acetylcholine (Kahan & LaBerge, 2011). agonists or to be an expert in cognitive training techniques. Lucid dreamers report being unable to perceive Unfortunately, we do not have enough space here to fine-grained visual details in their dreams (Kahan & instruct you ourselves, but fortunately there are several LaBerge, 2011). websites and books that can instruct you. The problem is that most of the techniques promoted are ineffective, or To date, only two studies have examined the brain changes worse, dangerous. What we can do is send you to a good associated with lucid dreaming—one case study (Dresler source: Exploring the World of Lucid Dreaming, a book by et al., 2012) and one quasiexperimental study (Baird et al., Stephen LaBerge, the most respected researcher in lucid 2018). Unfortunately, there was little consistency in their dreaming. If you have success, we would like to hear about results (see Baird, Mota-Rolim, & Dresler, 2019). your experiences. One would think everyone would want to be a lucid Why Do We Dream What We Do? dreamer. However, as the following case study illustrates, LO 14.7 Discuss the issue associated with studying it can be a mixed blessing. dream content and describe findings related to what can influence dream content. The Case of the Bored Lucid Most of us are fascinated by the content of our dreams. Dreamer People often seek out therapists who are self-proclaimed dream interpreters. Is it possible to interpret dreams? I (SB) was giving a lecture about dreaming. I told my students Sigmund Freud believed so (Freud, 1913). Freud about my own experiences with lucid dreaming and how believed that dreams are triggered by unacceptable wonderful it was. At the end of my story, I said, “I wish I could repressed wishes, often of a sexual nature. He argued that lucid dream every night.” because dreams represent unacceptable wishes, the dreams M14_PINE1933_11_GE_C14.indd 378 22/01/2021 15:27  Sleep, Dreaming, and Circadian Rhythms 379 we experience (our manifest dreams) are merely disguised versions of our real dreams (our latent dreams): He hypoth- esized 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 under- standing people and dealing with their psychological prob- lems is to expose the meaning of their latent dreams through the interpretation of their manifest dreams. There is no convincing scientific evidence for the Freudian theory of dreams; indeed, the brain science of the 1890s, which served as its foundation, is now obsolete. Yet many people still believe that dreams bubble up from a troubled unconscious and that they represent repressed thoughts and wishes. Although dream interpretation is no longer a focus of scientific research, biopsychologists are increasingly interested paul prescott/Shutterstock in understanding why we dream the content that we do. What do you see when you look at these clouds? If a researcher wants to study dream content, they must rely on the detailed self-reports of dreamers. This reliance largely random and that the resulting dream is the cortex’s on self-reports of dreams has been viewed as a problem by effort to make sense of these random signals. You might some, who question whether we can trust these self-reports liken this process to what happens when you stare up at the of dreams given that dream recall is often difficult if not clouds and see faces or figures in them: The clouds are ran- impossible for many (see Mangiaruga et al., 2018; Nir & domly patterned, but your brain is trying its best to make Tononi, 2010). Conversely, others have argued that self- sense of that random pattern. reports of dreams are a legitimate window into the world REVONSUO’S EVOLUTIONARY THEORY OF DREAMS. of dream content (see Cipolli et al., 2017; Windt, 2013). A second theory of why we dream is Revonsuo’s (2000) Despite the widely acknowledged limitations of dream evolutionary theory of dreams. According to this theory, recall and dream self-reports, studies of dream content have dreams serve an important biological function, and this flourished. Two key findings have emerged. First, there is a function has implications for the fitness of an organism general consensus that dream content is influenced by what in the Darwinian sense (see Chapter 2). Specifically, we have experienced in the prior period of wakefulness Revonsuo (2000) proposed that we dream to simulate (see Cipolli et al., 2017; Fogel et al., 2018)—even the most threatening events, such as physical attack, threats to social mundane of experiences, like taking out the garbage, can relationships, or threats to one’s livelihood, and that such enter a subsequent dream (see Vallat et al., 2017). Second, the simulation allows us to better predict and respond to amount of anxiety experienced prior to a bout of dreaming such threats when we are awake—see Gauchat et al. (2015). affects the emotional content of dreams (see Sikka, Pesonen, & Revonsuo, 2018; Vallat et al., 2017). HOBSON’S PROTOCONSCIOUSNESS HYPOTHESIS. In the years following the publication of his activation- synthesis hypothesis, Hobson began to believe there was a Why Do We Dream? purpose for dreaming and became increasingly critical of LO 14.8 Compare and contrast three different theories his own activation-synthesis hypothesis. of why we dream. Like Revonsuo (2000), Hobson now believed that dreaming conferred an evolutionary advantage. Unlike Rather than asking why we dream what we dream, many Revonsuo, his new protoconsciousness hypothesis proposed researchers are more interested in why we dream at all. that dreaming conferred that advantage by simulating What is dreaming good for, if anything? There are many everything, not just threatening situations. According to theories as to why we dream. In this section, we present his hypothesis, dreaming is important (1) during early three of the most prominent. development, when sensory input is limited by underdevel- HOBSON’S ACTIVATION-SYNTHESIS HYPOTHESIS. oped sensory systems—the visual system in particular, and One theory of why we dream is Hobson’s (1989) activation- (2) throughout one’s life, by anticipating and predicting synthesis hypothesis (see Palagini & Rosenlicht, 2011). It is how events will unfold while awake. based on the observation that, during sleep, many brain- In short, according to Hobson’s (2009) new theory, stem circuits become active and bombard the cerebral cortex dreaming is a training mechanism, with each dream repre- with neural signals. The essence of Hobson’s hypothesis is senting a virtual real-life scenario (see Boag, 2017; Hobson & that the information supplied to the cortex during sleep is Friston, 2012; Llewellyn, 2016; Scarpelli et al., 2019). Hence M14_PINE1933_11_GE_C14.indd 379 22/01/2021 15:27  380 Chapter 14 the term “protoconsciousness”: a virtual prototype of our There are two types of brain lesions that produce a ces- conscious experiences. sation of dreaming in patients (as determined either by self Hobson’s protoconsciousness hypothesis stands in stark report, by in-lab sleep studies, or both): (1) bilateral lesions contrast to his earlier activation-synthesis hypothesis, which of the temporo-parieto junction (that location in the cerebral proposed that dreams are, in essence, leftovers from a brain cortex where the temporal lobes and the parietal lobes built for a day job that serves no particular function. It might meet), and (2) bilateral lesions of the medial prefrontal cortex; strike you as odd that a researcher would propose a theory see Figure 14.4 (see Domhoff & Fox, 2015; Vallat et al., 2018). that contradicts his own theory. However, this is a sign of In addition, lesions to those areas of secondary visual cortex good critical thinking: In order to think critically, one must in the medial occipital lobe lead to a loss of visual imagery be just as critical of one’s own theories as one is of others’. in dreams (see Figure 14.4). There have been many fMRI (see Chapter 5) studies of The Dreaming Brain healthy participants engaged in REM sleep (see Domhoff & Fox, 2015). Consistent with the lesion studies, the LO 14.9 Identify three brain areas that have been temporo-parieto junction, the medial prefrontal cortex, implicated in dreaming. and medial occipital cortex all display increased neural What brain areas are involved in dreaming? Studies of activity during REM sleep (see Figure 14.4; Domhoff & patients with brain lesions and neuroimaging studies of Fox, 2015). Whether NREM dreams are associated with individuals dreaming tell a clear story. comparable patterns of brain activation remains to be Figure 14.4 Two areas of the brain implicated in dreaming and one implicated in visual imagery. Both lesions studies and brain imaging studies have implicated the medial prefrontal cortex and the tempero-parieto junction in dreaming. Both lesion studies and brain imaging studies have implicated the medial occipital lobe in the visual imagery within dreams. Medial prefrontal cortex Medial occipital lobe Temporo-parieto junction Adapted from Figure 1 of Domhoff, G. W., & Fox, K. C. (2015). Dreaming and the default network: A review, synthesis, and counterintuitive research proposal. Consciousness and Cognition, 33, 342–353. M14_PINE1933_11_GE_C14.indd 380 22/01/2021 15:27  Sleep, Dreaming, and Circadian Rhythms 381 seen (see Mutz & Javadi, 2017). We know of only one no role in the efficient physiological functioning of the body. study that has addressed the neuroanatomical correlates According to these theories, early humans had enough time of NREM dreaming. The study by Siclari et al. (2017) to get their eating, drinking, and reproducing out of the way demonstrated that activity in the tempero-parieto junction during the daytime, and their strong motivation to sleep was associated with both REM and NREM dreaming, at night evolved to conserve their energy resources, make suggesting that this brain region is critical for dreaming them less susceptible to mishaps in the dark (e.g., predation) in general. (Joiner, 2016), and to carry out certain brain functions that aren’t possible during wakefulness (see Chen & Wilson, 2017; Frank, 2017; Nagai et al., 2017; Stickgold, 2015). Adaptation theories suggest that sleep is like reproductive Why Do We Sleep, behavior in the sense that we are highly motivated to engage in it, but we don’t need it to stay healthy. and Why Do We Sleep It should be noted that this distinction between recu- When We Do? peration theories and adaptation theories of sleep does not mean that a specific theory cannot incorporate elements of You have been introduced to the properties of sleep and its both. For example, a theory of sleep might propose that we various stages, and you have also learned about the topic of have evolved to sleep at night, but that the duration of our dreaming. The focus of this chapter now shifts to a consid- nightly sleep is determined by recuperative mechanisms eration of two fundamental questions about sleep: Why do (e.g., Eban-Rothschild, Giardino, & de Lecea, 2017; Yadav we sleep? And why do we sleep when we do? et al., 2017). Two Kinds of Theories of Sleep Comparative Analysis of Sleep LO 14.10 Describe the two kinds of theories of sleep. LO 14.11 Explain four conclusions that have resulted Two kinds of theories of sleep have been proposed: recuperation from the comparative analysis of sleep. theories and adaptation theories. The differences between these Sleep has been studied in only a small number of species, two theoretical approaches are revealed by the answers they but the evidence so far suggests that all mammals and most offer to the two fundamental questions about sleep. birds sleep (see Manger & Siegel, 2020). Furthermore, the The essence of recuperation theories of sleep is that sleep of mammals and birds, like ours, is characterized by being awake disrupts the homeostasis (internal physiological high-amplitude, low-frequency EEG waves punctuated stability) of the body in some way and sleep is required to by periods of low-amplitude, high-frequency waves restore it. Various recuperation theories differ in terms of the (see Manger & Siegel, 2020). The evidence for sleep in particular physiological disruption they propose as the trigger amphibians, reptiles, fish, and insects is less clear: Some for sleep. For example, the three most common recuperation display periods of inactivity and unresponsiveness, but theories of sleep are that the function of sleep is to (1) restore the relation of these periods to mammalian sleep has not energy levels that decline during wakefulness (see Porkka- been established (see Siegel, 2008; Zimmerman et al., 2008). Heiskanen, 2013), (2) clear toxins (e.g., beta-amyloid—see Table 14.2 gives the average number of hours per day that Chapter 10) from the brain and other tissues that accumu- various mammalian species spend sleeping. late during wakefulness (see Da Mesquita et al., 2018; Holth et al., 2019; Lei et al., 2017; Sun et al., 2018; Sweeney & ­Zlokovic, 2018), or (3) restore the synaptic plasticity that might Journal Prompt 14.1 dissipate during wakefulness (see Cirelli & Tononi, 2015; If you were a sleep researcher studying sleep in various de Vivo et al., 2017; Tononi & Cirelli, 2019). However, regard- organisms, how would you define sleep? less of the particular function postulated by recuperation theories of sleep, they all imply that sleepiness is triggered by a deviation from homeostasis caused by wakefulness and The comparative investigation of sleep has led to sev- that sleep is terminated by a return to homeostasis. eral important conclusions. Let’s consider four of these. The essence of adaptation theories of sleep is that sleep First, the fact that most mammals and birds sleep (see is not a reaction to the disruptive effects of being awake but Siegel, 2012) suggests that sleep serves some important the result of an internal 24-hour timing mechanism—that physiological function, rather than merely protecting ani- is, we humans are programmed to sleep at night regardless mals from mishap and conserving energy. The evidence is of what happens to us during the day. Adaptation theories strongest in species that are at increased risk of predation of sleep focus more on when we sleep than on the function of when they sleep (e.g., antelopes) and in species that have sleep. Some of these theories even propose that sleep plays evolved complex mechanisms that enable them to sleep. For M14_PINE1933_11_GE_C14.indd 381 22/01/2021 15:27  382 Chapter 14 Table 14.2 Average Number of Hours Slept per Day by Figure 14.5 After gorging themselves on a kill, African Various Mammalian Species lions often sleep almost continuously for 2 or 3 days. And where do they sleep? Anywhere they want! Hours of Sleep Mammalian Species per Day Giant sloth 20 Opossum, brown bat 19 Giant armadillo 18 Owl monkey, nine-banded armadillo 17 Arctic ground squirrel 16 Tree shrew 15 Cat, golden hamster 14 Mouse, rat, gray wolf, ground squirrel 13 Arctic fox, chinchilla, gorilla, raccoon 12 Mountain beaver 11 Jaguar, vervet monkey, hedgehog 10 CRSuber/Getty Images Rhesus monkey, chimpanzee, baboon, 9 red fox Fourth, many studies have tried to identify the rea- Human, rabbit, guinea pig, pig 8 sons why some species are long sleepers and others Gray seal, gray hyrax, Brazilian tapir 6 are short sleepers. Why do cats tend to sleep about Tree hyrax, rock hyrax 5 14 hours a day and horses only about 2? Under the influ- Cow, goat, elephant, donkey, sheep 3 ence of recuperation theories, researchers have focused on energy-related factors in their efforts. However, there Roe deer, horse, zebra 2 is no strong relationship between a species’ sleep time and its level of activity, its body size, or its body tem- perature (see Siegel, 2005). The fact that giant sloths sleep example, some birds and marine mammals sleep with only 20 hours per day is a strong argument against the theory that half of their brain at a time so that the other half can con- sleep is a compensatory reaction to energy expenditure— trol resurfacing for air (e.g., Lyamin et al., 2018; Lyamin & similarly, energy expenditure has been shown to have Siegel, 2019; Mascetti, 2016; Yadav et al., 2017). It is against little effect on subsequent sleep in humans (see Kelley & the logic of natural selection for some animals to risk preda- Kelley, 2017). In contrast, adaptation theories correctly tion while sleeping and for others to have evolved complex predict that the daily sleep time of each species is related mechanisms to permit them to safely sleep, unless sleep to how vulnerable it is while it is asleep and how much itself serves some critical function. time it must spend each day to feed itself and to take care Second, the fact that most mammals and birds sleep of its other survival requirements. For example, zebras suggests that the primary function of sleep is not some must graze almost continuously to get enough to eat and special, higher-order human function. For example, sug- are extremely vulnerable to predatory attack when they gestions that sleep helps humans reprogram our complex are asleep—and they sleep only about 2 hours per day. In brains or that it permits some kind of emotional release to contrast, African lions often sleep more or less continu- maintain our mental health are improbable in view of the ously for 2 or 3 days after they have gorged themselves comparative evidence. on a kill. Figure 14.5 says it all. 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 (see Table 14.2). Horses and many other animals get by quite Effects of Sleep Deprivation nicely on 2 or 3 hours of sleep per day. Moreover, it is impor- One way to identify the functions of sleep is to determine tant to realize that the sleep patterns of mammals and birds what happens when a person is deprived of sleep. This in their natural environments can vary substantially from module begins with a cautionary note about the inter- their patterns in captivity, which is where they are typically pretation of the effects of sleep deprivation, a description studied. For example, some animals that sleep a great deal of the predictions that recuperation theories make about in captivity sleep little in the wild when food is in short sleep deprivation, and two classic case studies of sleep supply or during periods of migration or mating (see Lesku deprivation. Then, it summarizes the results of sleep- et al., 2012; Siegel, 2012). deprivation research. M14_PINE1933_11_GE_C14.indd 382 22/01/2021 15:27  Sleep, Dreaming, and Circadian Rhythms 383 Interpretation of the Effects of Sleep Two Classic Sleep-Deprivation Case Deprivation: The Stress Problem Studies LO 14.12 Explain how stress can often be a confounding LO 14.14 Describe two classic sleep-deprivation case variable when considering the effects of sleep studies. deprivation. Let’s look at two widely cited sleep-deprivation case stud- When you sleep substantially less than you are used to, the ies. First is the groundbreaking study of a group of sleep- next day you feel out of sorts and unable to function as deprived students (Kleitman, 1963); second is the bizarre well as you usually do. Although such experiences of sleep case of Randy Gardner (Dement, 1978). deprivation are compelling, you need to be cautious in inter- preting them. In Western cultures, most people who sleep little or irregularly do so because they are under stress (e.g., The Case of the Sleep-Deprived from illness, excessive work, shift work, drugs, or exami- Students nations), which could have adverse effects independent of any sleep loss. Even when sleep-deprivation studies are Most of the volunteer students subjected to total sleep depriva- conducted on healthy volunteers in controlled laboratory tion by Kleitman experienced the same effects. During the first environments, stress can be a contributing factor because night, they read or studied with little difficulty until after 3:00 a.m., many of the volunteers will find the sleep-deprivation pro- when they experienced an attack of sleepiness. At this point, cedure itself stressful. Accordingly, because it is difficult to their watchers had to be particularly careful that they did not separate the effects of sleep loss from the effects of stressful sleep. The next day the students felt alert as long as they were conditions that may have induced the loss, results of sleep- active. During the second night, reading or studying was next deprivation studies must be interpreted with caution. to impossible because sleepiness was so severe, and as on the first night, there came a time after 3:00 a.m. when sleepiness Be that as it may, almost every week we read a news became overpowering. However, as before, later in the morn- article decrying the effects of sleep loss in the general pop- ing, there was a decrease in sleepiness, and the students could ulation. Such articles will typically point out that many perform tasks around the lab during the day as long as they people who are pressured by the demands of their work were standing and moving. schedule sleep little and experience a variety of health and The cycle of sleepiness on the third and fourth nights accident problems. There is a place for this kind of research resembled that on the second, but the sleepiness became even because it identifies a public health issue that requires atten- more severe. Surprisingly, things did not grow worse after the tion (see Chattu et al., 2018); however, because the low lev- fourth night, and those students who persisted repeatedly went els of sleep are hopelessly confounded with high levels through the same daily cycle. of stress (see Anafi, Kayser, & Raizen, 2019), most sleep- deprivation studies tell us little about the functions of sleep and how much we need. The Case of Randy Gardner Predictions of Recuperation Theories Randy Gardner and two classmates, who were entrusted with about Sleep Deprivation keeping him awake, planned to break the then world record of LO 14.13 List the three predictions that recuperation 260 hours of consecutive wakefulness. Dement learned about theories make about the effects of sleep the project and, seeing an opportunity to collect some impor- tant data, joined the team, much to the comfort of Randy’s deprivation. parents. Randy did complain vigorously when his team would Because recuperation theories of sleep are based on the not permit him to close his eyes. However, in no sense could premise that sleep is a response to the accumulation of some Randy’s behavior be considered disturbed. Near the end of debilitating effect of wakefulness, they make the following his vigil, Randy held a press conference, and he conducted three predictions about sleep deprivation: ­himself impeccably. Randy went to sleep exactly 264 hours and 12 minutes after he had awakened 11 days before. And how Long periods of wakefulness will produce physiologi- long did he sleep? Only 14 hours the first night, and thereafter cal and behavioral disturbances. he returned to his usual 8-hour schedule. These disturbances will grow worse as the sleep depri- vation continues. After a period of deprivation has ended, much of the Although you may be surprised that Randy did not missed sleep will be regained. have to sleep longer to “catch up” on his lost sleep, the lack Have these predictions been confirmed? of substantial recovery sleep is typical of such cases. M14_PINE1933_11_GE_C14.indd 383 22/01/2021 15:27  384 Chapter 14 Studies of Sleep Deprivation systematic investigation. For example, several researchers have pointed out the need to determine the degree to which in Humans the deficits in vigilance and motivation produced by sleep LO 14.15 Describe the major effects of sleep deprivation loss can be mistaken for cognitive deficits (see Axelsson et al., in humans. 2019; Basner et al., 2013; Engle-Friedman, 2014; Massar, Lim, & Huettel, 2019). Since the first studies of sleep deprivation by Dement and Kleitman in the mid-20th century, there have been hun- dreds of studies assessing the effects on humans of sleep- Journal Prompt 14.2 deprivation schedules ranging from a slightly reduced Why would deficits in vigilance and motivation lead amount of sleep during one night to total sleep depriva- to cognitive deficits? Give an example as part of your answer. tion for several nights (see Krause et al., 2017). The studies have assessed the effects of these schedules on many differ- ent measures of sleepiness, mood, cognition, motor perfor- The adverse effects of sleep deprivation on physical mance, physiological function, and even molecular function performance have been surprisingly inconsistent consider- (see Krause et al., 2017). ing the general belief that a good night’s sleep is essential Even moderate amounts of sleep deprivation—for for optimal motor performance. Only a few measures tend example, sleeping 3 or 4 hours less than normal for one to be affected (e.g., Patrick et al., 2017), even after lengthy night—have been found to have three consistent effects. periods of deprivation, and there are indications that the First, sleep-deprived individuals display an increase in effects on these measures are unreliable (see Fullager et al., sleepiness: They report being more sleepy, and they fall 2015; Knufinke et al., 2018; Vaara et al., 2018). Altogether, the asleep more quickly if given the opportunity. Second, study of the effects of sleep ­deprivation on physical perfor- sleep-deprived individuals display negative affect on mance remains controversial (see Vaara et al., 2018). various tests of mood. And third, they perform poorly Sleep deprivation has been found to have a variety of on tests of sustained attention (e.g., watching for a mov- physiological consequences such as reduced body tempera- ing light on a computer screen)—see Kirszenblat and van ture, increases in blood pressure, decreases in some aspects Swinderen (2015). of immune function, hormonal changes, and metabolic The effects of sleep deprivation on complex cognitive changes (see Cedernaes, Schiöth, & Benedict, 2015; Irwin, functions have been less consistent (see Basner et al., Olmstead, & Carroll, 2016; Maggio et al., 2013). The problem 2013) and show marked variability between individuals— is that there is little evidence that these changes have any ranging from virtually no effects to severe effects (see Krause consequences for health or performance. For example, the et al., 2017; Satterfield & Killgore, 2019). Consequently, fact that a decline in immune function was discovered in researchers have preferred to assess performance on sleep-deprived volunteers does not necessarily mean that the simple, dull, monotonous tasks most sensitive to the they would be more susceptible to infection—the immune effects of sleep deprivation, such as tasks that require system is extremely complicated and a decline in one aspect sustained attention (see Hudson, Van Dongen, & Honn, is often compensated for by other changes. This is why we 2019; Satterfield & Killgore, 2019). Nevertheless, a large want to single out a study by Prather and colleagues (2015) number of studies have been able to demonstrate disruption for commendation: Rather than studying immune function, of the performance of complex cognitive tasks by sleep these researchers focused directly on susceptibility to infec- deprivation (see Basner et al., 2013; Krause et al., 2017). tion and illness. The inconsistent effects of sleep deprivation on Prather and colleagues exposed 164 healthy volun- cognitive function in various studies was clarified by the teers to a cold virus. Those who slept less than 6 hours a discovery that only some cognitive functions appear to night were not less likely to become infected, but they were be susceptible. Many early studies of the effects of sleep more likely to develop a cold. This is a correlational study deprivation on cognitive function used tests of logical (see Chapter 1), and thus it cannot directly implicate sleep deduction or critical thinking, and these tests proved to be duration as the causal factor. Still, the suggestion that there largely immune to disruption. In contrast, performance on may be a causal relation between sleep and susceptibility to tests of executive function proved to be more susceptible infection warrants further research. to disruption by sleep loss. Executive function is a group After 2 or 3 days of continuous sleep deprivation, of cognitive abilities, such as problem solving, working most volunteers experience microsleeps, unless they are memory, decision making, and assimilating new information in a laboratory environment where the microsleeps can be to update plans and strategies (see Miller & Wallis, 2009). interrupted as soon as they begin. Microsleeps are brief The hypothesis that only some cognitive processes are periods of sleep, typically about 2 or 3 seconds long, during susceptible to disruption by sleep loss clearly requires more which the eyelids droop and the volunteers become less M14_PINE1933_11_GE_C14.indd 384 22/01/2021 15:27  Sleep, Dreaming, and Circadian Rhythms 385 responsive to external stimuli, even though they remain Figure 14.6 The carousel apparatus used to deprive an sitting or standing (see Toppi et al., 2016). As one would experimental rat of sleep while a yoked control rat is exposed expect, microsleeps severely disrupt the performance of to the same number and pattern of disk rotations. The disk tests of vigilance, but even sleep-deprived individuals on which both rats stand rotates every time the experimental not experiencing microsleeps experience some vigilance rat displays sleep EEG. If the sleeping rat does not awaken problems (see Hudson, Van Dongen, & Honn, 2019). immediately, it is deposited in the water. It can be useful to compare sleep deprivation with Yoked control rat the deprivation of the motivated behaviors discussed in Experimental rat Chapters 12 and 13. If people were deprived of the oppor- Rotating disk tunity to eat or engage in sexual activity, the effects would Water be severe and unavoidable: In the first case, starvation and death would ensue; in the second, there would be a total loss of reproductive capacity. Despite our powerful drive to sleep, the effects of sleep deprivation tend to be com- paratively subtle, selective, and variable (see Satterfield & Killgore, 2019; Vaara et al., 2018). This is puzzling. Another puzzling thing is that performance deficits observed after extended periods of sleep deprivation disappear so read- ily—for example, in one study, 4 hours of sleep eliminated the performance deficits produced by 64 hours of sleep deprivation (Rosa, Bonnet, & Warm, 2007). Sleep-Deprivation Studies of Laboratory Animals Based on Rechtschaffen, A., Gilliland, M. A., Bergmann, B. M., & Winter, J. B. (1983). Physiological correlates of prolonged sleep deprivation in rats. LO 14.16 Describe the key studies of sleep deprivation Science, 221, 182–184. in laboratory animals. Provide a critique of the carousel apparatus as a method of sleep postmortem examination: swollen adrenal glands, gastric deprivation. ulcers, and internal bleeding (see Geissmann, Beckwith, & The carousel apparatus (see Figure 14.6) has been used to Gilestro, 2019). deprive rats of sleep. Two rats, an experimental rat and You have already encountered many examples in this its yoked control, are placed in separate chambers of the text of the value of the comparative approach. However, apparatus. Each time the EEG activity of the experimental sleep deprivation may be one phenomenon that cannot be rat indicates that it is sleeping, the disk, which serves as productively studied in nonhumans because of the unavoid- the floor of half of both chambers, starts to slowly rotate. able confounding effects of extreme stress (see McEwen & As a result, if the sleeping experimental rat does not Karatsoreos, 2015; Minkel et al., 2014). awaken immediately, it gets shoved off the disk into a shallow pool of water. The yoked control is exposed to REM-Sleep Deprivation exactly the same pattern of disk rotations; but if it is not LO 14.17 Describe the effects of REM-sleep deprivation. sleeping, it can easily avoid getting dunked by walking in the direction opposite to the direction of disk rotation. Because of its early association with dreaming, REM sleep The experimental rats typically died after about 12 days, has been the subject of intensive investigation. In an effort to while the yoked controls stayed reasonably healthy (see reveal the particular functions of REM sleep, sleep research- Rechtschaffen & Bergmann, 1995). ers have specifically deprived sleeping volunteers of REM The fact that humans and rats have been sleep-deprived sleep by waking them up each time a bout of REM sleep by other means for similar periods of time without dire con- begins. sequences argues for caution in interpreting the results of REM-sleep deprivation has been shown to have two the carousel sleep-deprivation experiments (see Rial et al., consistent effects (see Figure 14.7). First, following REM- 2007; Siegel, 2009, 2012). It may be that repeatedly being sleep deprivation, participants display a REM rebound; awakened by this apparatus kills the experimental rats not that is, they have more than their usual amount of REM because it keeps them from sleeping but because it is stress- sleep for the first two or three nights (Lyamin et al., 2018; ful. This interpretation is consistent with the pathological McCarthy et al., 2016). Second, with each successive night problems in the experimental rats that were revealed by of deprivation, there is a greater tendency for participants M14_PINE1933_11_GE_C14.indd 385 22/01/2021 15:27  386 Chapter 14 believe that REM sleep strengthens explicit Figure 14.7 The two effects of REM-sleep deprivation. memories (see Diekelmann & Born, 2010)— particularly those with emotional content (see 80 Number of Times Participants Morgenthaler et al., 2014; Wiesner et al., 2015), Were Awakened to Enforce REM-Sleep Deprivation other researchers believe that slow-wave sleep 60 promotes memory consolidation (see Euston & Steenland, 2014; Inostroza & Born, 2013; Tononi 40 & Cirelli, 2013), and still others believe that the memories of our daily experiences are processed 20 (e.g., modified) prior to consolidation during sleep (see Chatburn, Lushington, & Kohler, 2014; 0 Dudai, Karni, & Born, 2015; Stickgold & Walker, 0 1 2 3 4 5 6 7 8 2013). However, overall the results are still not Nights of REM-Sleep Deprivation convincing: Some studies have not observed any relationship between memory and sleep (see The number of awakenings required to deprive a participant of REM sleep increases as the period of deprivation ensues. Ackermann et al., 2015). The sleep of depressed patients constitutes a serious challenge to the hypothesis that sleep influ- REM-sleep Predeprivation Postdeprivation ences memory. Treated with antidepressant drugs, deprivation they may experience no REM sleep for years, again Time Spent in REM Sleep Percent of Total Sleep 30% with no experience of memory deficits (see Genzel et al., 2014; Tribl, Wetter, & Schredl, 2013). The default theory of REM sleep is a different 20% approach to understanding the functions of REM sleep (see Horne, 2013). According to this theory, 10% it is difficult to stay continuously in NREM sleep, so the brain periodically switches to one of two 0% other states. If there are any immediate bodily 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 needs to be taken care of (e.g., the need for food Nights or water), the brain switches to wakefulness; if After a period of REM-sleep deprivation, participants spend a there are no immediate needs, it switches to REM greater than usual portion of their sleep time in REM sleep. sleep. According to the default theory, REM sleep is more adaptive than wakefulness when there are no immediate bodily needs. In addition, accord- to initiate REM sleep. Thus, as REM-sleep deprivation ing to the default theory, REM sleep functions to prepare proceeds, participants have to be awakened more and more organisms for wakefulness in natural environments where frequently to keep them from accumulating significant immediate effective activity may be required upon waken- amounts of REM sleep (see Maisuradze, 2019; McCarthy