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139Unit 3 The conscious self

Learning Activity 3.1Review questions1 Whatissleep?2 Whyissleepconsideredtobeanaltered

stateofconsciousness?3 Whatispolysomnography?4 Describehowself-reportsmaybeusedto

studysleep.5 Constructatablethatsummarisesthe

recordingdevicesthatmaybeusedinasleepstudy.Headingsshouldincludename of device, descriptionandwhat it measuresinrelationtosleep.

Characteristics and patterns of sleepOver the course of a typical night’s sleep we experience two distinctly different states, or types, of sleep known as NREM sleep (non-rapid-eye-movement sleep) and REM sleep (rapid-eye-movement sleep). These occur in continuous cycles, with one following the other. In adults, one cycle of NREM sleep lasts for about 70 to 90 minutes, and consists of four distinct stages, each of which can be identified by a different brain wave pattern. As shown in figure 3.9, a period of REM sleep follows each period of NREM sleep.

Consequently, some researchers refer to REM sleep as a fifth stage of sleep. A complete sleep cycle consists of a period of NREM sleep (but not necessarily all four NREM stages) and a period of REM sleep (which tends to increase in duration as the night progresses). Generally a complete sleep cycle lasts for about 80 to 120 minutes, and we go through this cycle approximately four or five times during eight hours of sleep each night.

NREM sleepApproximately 80% of our sleep time is spent in NREM sleep, and typically the first half of the night has more NREM sleep than the second half of the night (see figure 3.9). During NREM sleep the brain is active (as shown by EEG recordings), but not as active as during REM sleep, or during normal waking consciousness. Some psychologists have proposed that NREM sleep may be the time when the body recovers, repairing body tissue, removing waste products and replenishing neurotransmitters that are vital to communication between neurons (Inoue & others, 1995). For example, research on the effects of strenuous physical activity on subsequent sleep patterns indicates that deep sleep experienced in NREM sleep increases during nights after vigorous exercise (Vein & others, 1991).

Awake

Stage 1

0

Stage 2

Stage 3

Stage 4

1 2 3 4 5 6 7Hours of sleep

REM

NREM

Figure 3.9 During an eight-hour sleep period in a typical night, we experience four or five complete cycles of sleep consisting of NREM and REM sleep periods. Note that NREM sleep has four different stages and that stage 3 and 4 (deepest sleep) may not be experienced as morning approaches. Furthermore, as sleep progresses, periods of REM sleep tend to get longer and be closer together.

VCE Psych ch03.indd 139 28/07/10 12:57 PM

johnky

Text Box

The following are sample pages from: Grivas, J. & Carter, L, (2010) Psychology VCE Units 3&4, 4th Ed.

Chapter 3 Sleep140

Figure 3.10 NREM and REM sleep are characterised by different brain wave patterns recorded by the EEG. When we are in NREM sleep, brain waves gradually decrease in frequency and increase in amplitude as we progress from lighter through to deeper sleep. When we are in REM sleep, the brain waves are similar to those that are recorded when we are awake and alert.

AWAKE

Alert—beta waves (13–30 cycles/seconds)

Resting—hypnogogic state—alpha waves

NREM SLEEP

Stage 1—mix of alpha and theta waves (8–12 cycles/second)

Stage 2—mostly theta waves, plus occasional sleep spindles and K complex (3–7 cycles/second)

sleep spindle

K complex

Stage 3—mix of theta waves and delta waves

Stage 4—more than 50% delta waves ( –2 cycles/second)

REM SLEEP

Irregular fast waves; like beta waves

12


johnky

Callout

NOTE: We will learn more about how brain waves are measured next week.


NREM sleep consists of four different stages in which the sleeper progresses from a stage of light sleep to the stage of deepest sleep and back again through one or more stages to light sleep. Psychologists can determine an individual’s stage of sleep by examining the characteristics of EEG recordings. Every stage of sleep is dominated by a particular identifiable brain wave pattern or rhythm that is different from that of the other stages. Each brain wave pattern can be distinguished in terms of two characteristics: the number of brain waves and the intensity of the brain waves. The term frequency is used to describe the number of brain waves. For example, low frequency would refer to relatively few brain waves (per second) or ‘slow’ brain wave activity, and high frequency would refer to a lot of brain waves (per second) or ‘fast’ brain wave activity. The term amplitude is used to describe the intensity of the brain waves and is estimated by the size of the brain waves; for example, the peaks (‘highs’) and troughs (‘lows’) evident in the pattern of activity (see figure 3.10).

It has been found that when we first close our eyes and begin to relax before actually going to sleep, our brain emits bursts of alpha waves. Alpha wave patterns are associated with relaxation and drowsiness and are characterised by a fairly regular pattern of relatively high-frequency and medium-amplitude brain waves, as recorded by the EEG. This transition period from being awake to being asleep is sometimes called the hypnogogic state, or the twilight stage of sleep, and it is characterised by slow, rolling eye movements. During this stage, which may last for a minute or two, some people experience flashes of light or colour, feelings of floating and weightlessness, dreamlike images that resemble vivid photographs, or swift, jerky movements and a sense of falling or slipping. In this pre-sleep stage our body is winding down and beginning to drift towards the first stage of the NREM sleep cycle.

NREM—stage 1Stage 1 in the NREM sleep cycle occurs as we drift into and out of a true sleep state. We tend to gradually lose awareness of ourselves and our surroundings, but some of the time we are actually aware of faint sounds in our environment (Coren, 1996). Physiological changes that indicate a lower level of bodily arousal—such as a decrease in heart

rate, respiration, body temperature and muscle tension—are all evident in stage 1. As a result of the muscles relaxing, we sometimes experience a ‘jerking’ sensation whereby our body, or a part of our body, seems to go into a spasm. This is known as a hypnic jerk and it is a common occurrence during stage 1. In addition, the EEG pattern shows a decrease in alpha wave production as these brain waves are replaced by more irregular medium-frequency theta waves, which have a mixture of high and low amplitude. Stage 1 lasts for about five to ten minutes. If we are woken during this stage, we may feel we have not been asleep at all.

NREM—stage 2Stage 2 of NREM sleep is a light stage of sleep, and some researchers identify this as the point at which someone can be said to be truly asleep. Although our sleep is less easily disturbed than it is in stage 1, we can still be easily aroused from this sleep stage (Coren, 1996). During stage 2, which lasts for about ten to 20 minutes, body movements lessen, breathing becomes more regular, blood pressure and temperature continue to fall, and heart rate is slower. Brain waves are mainly theta waves, but are slightly lower in frequency and higher in amplitude than the theta waves produced in stage 1. During stage 2, brief bursts of higher frequency brain wave activity called sleep spindles periodically appear on the EEG recording. A burst of sleep spindles lasts for about one second, and their presence is an indicator that the person is truly asleep.

Although we are asleep, the brain still responds to various external and internal stimuli, such as the sound of a knock on a door, or muscle tension in a leg as we move. EEG patterns also show bursts of low frequency and slightly higher amplitude waves, called K complexes, in response to arousing stimuli (Halasz, 1993) (see figure 3.10). About midway through stage 2, we are unlikely to respond to anything except extremely strong or loud stimuli, indicating that sleep has become noticeably deeper. In comparison to stages 3 and 4 NREM sleep, stage 2 NREM sleep is still considered to be light sleep—if you awaken people from this stage, about seven out of ten will tell you that they really didn’t think they were asleep, but were just dozing and thinking (Coren, 1996).


Chapter 3 Sleep142

NREM—stage 3Stage 3 is the start of the deepest period of sleep, and lasts for about ten minutes. Stage 3 might be best called moderately deep sleep (Coren, 1996). Heart rate, blood pressure and body temperature continue to drop, and breathing rate continues to be slow and steady. The individual is extremely relaxed and becomes less and less responsive to the outside world. In this stage, people are difficult to arouse, but if they are awoken they are often groggy and disoriented. EEG activity is also noticeably different from that of earlier NREM stages. During stage 3, there is a reduction in the brain’s electrical activity, and delta waves begin to appear in the EEG recording. Delta waves make up about 20–50% of the brain waves recorded during stage 3, being slow, large, regular brain waves. They are lower in frequency and higher in amplitude than the alpha and theta waves of stages 1 and 2.

The presence of delta waves marks the beginning of slow wave sleep (SWS), so called because of the slower frequency delta waves. Generally, we begin SWS within an hour of falling asleep, and remain in SWS for about 30 minutes. When the EEG recordings show that delta waves comprise more than 50% of the brain wave activity, the person has entered stage 4, the deepest stage of sleep, and they will be extremely difficult to rouse.

NREM—stage 4Stage 4 is the deepest stage of sleep. It might best be called very deep sleep (Coren, 1996). The physiological signs of NREM stage 4 are similar to those in NREM stage 3 and, in fact, some recent classifications merge stages 3 and 4. In addition, muscles are completely relaxed and we barely move. Delta waves dominate the EEG pattern and are even slower and larger than those in stage 3. A person in stage 4 is very difficult to wake. It is the point at which people are often said to be ‘sleeping like a log’ or ‘out like a light’. When they are woken, they can take up to ten minutes to orient themselves, and usually have a poor memory of sleep events. This is sometimes referred to as ‘sleep drunkenness’, although psychologists prefer the term sleep inertia when referring to the post-awakening ‘mental lag’.

In the first cycle of sleep, a person may spend up to 20 minutes in stage 4. However, as the night progresses, less and less time is spent in stages 3 and 4. In sleep cycles close to the morning, there may be no stage 3 or 4 sleep at all (see figure 3.9). This has led to the belief that ‘sleep before midnight’ is best because it may be the most beneficial and rejuvenating sleep, since people deprived of stage 4 sleep often complain of muscle aches and tension.

It is during the very deep sleep of stages 3 and 4 that sleep phenomena such as sleepwalking, sleep talking and night terrors occur. It is also the period of sleep when bedwetting may occur (more so than

Figure 3.11 Like humans, cats experience both NREM and REM sleep periods. (a) However, a cat in NREM sleep often remains upright. (b) With the onset of REM sleep, the muscles completely relax and the cat lies down.

a b



in other stages).The progression through the NREM sleep

cycle from stage 1 to stage 4 takes about 45 to 60 minutes before we progressively move back up through stages 3 and 2. Having passed through one complete NREM sleep cycle, we do not awaken, although our brain and body begin to respond as if we are on the point of waking up. These are signs that we are about to move into REM sleep.

REM sleepAs the term suggests, REM sleep is a period of rapid-eye-movement sleep during which the eyeballs rapidly move beneath the closed eyelids, darting back and forth and up and down in jerky movements. The brain wave pattern associated with REM sleep is irregular, consisting of low-amplitude, relatively high-frequency beta waves like those produced during alert wakefulness. However, REM sleep is considered to be deep sleep because people are difficult to wake during this period.

The body’s internal functioning is more active during REM sleep than during NREM sleep. The heart rate is faster and more irregular. Blood pressure rises, and breathing is quicker and more irregular. However, the sleeper is totally relaxed. Although there are occasional twitching movements in the small muscles of the face,

fingers and toes, most of the skeletal muscles (that is, those attached to bones) are limp, and the body shows few outward signs of movement. An observer might say the sleeper appears paralysed during REM sleep. Consequently, REM sleep is called paradoxical sleep—internally, the brain and body are active, while, externally, the body appears calm and inactive. The purpose of the apparent body paralysis is still unknown. However, some psychologists have suggested that it may have evolved to prevent us from acting out our dreams, and thereby minimise any potential harm (Pressman & Orr, 1997).

Research indicates that it is during REM sleep that most dreaming occurs. In sleep laboratories, if a research participant is woken during REM sleep, about 80% of the time they will report having been dreaming at the time of being woken. Although some people believe they do not dream, research findings suggest that we dream several times a night, even though we may not remember dreaming. Dreaming also occurs during NREM sleep, but the dreams are less frequent, less memorable, less vivid and less fragmented than those of REM dreams. Some people believe that the rapid eye movements characteristic of REM sleep correspond to activity in dreams. However, it has been found that a dreamer’s eye movements are unrelated to the content of their dreams.

Figure 3.13 These double-exposure photographs capture the rapid eye movements of REM sleep, during which vivid dreaming occurs, as do heightened levels of physiological functioning.

Figure 3.12 Night terrors tend to occur during the very deep sleep of stages 3 and 4. A person experiencing a night terror may awaken suddenly, screaming and perspiring profusely. Unlike the experience of a nightmare, a person has little or no recall of their night terror episode on awakening.


Chapter 3 Sleep144

Figure 3.14 Brain wave patterns, as shown by an EEG, EOG and EMG

(a)

(b) State ofconsciousness

Physiological sleep measures

EOG10 seconds

EEG1 second

Awake—alert

NREM—stage 1

NREM—stage 2

NREM—stage 3

NREM—stage 4

REM

EMG10 seconds



Some researchers believe that eye movements are simply physiological activity that is occurring at the same time as random neural activity of the brain. Although many psychologists support this view, the specific reason for the eye movements is unclear.

Throughout the night, we pass continuously

through NREM and REM sleep cycles, with REM periods lengthening and occurring closer together as the night progresses. A REM period that occurs early in the night may last for only a few minutes, while a later REM period may last up to an hour or so. This may explain why you are often dreaming when you are woken by an alarm in the morning.

Box 3.2

Y.H. was referred to a sleep laboratory because he had been waking during the night in a panic and shouting loudly. Sleep researchers believed these experiences could have been either associated with nightmares during REM sleep or with night terrors, which occur mainly during stages 3 and 4 of NREM sleep. Y.H. was an Israeli Army veteran who had sustained brain damage from shrapnel during the ‘War of Attrition’ in the early 1970s. He was confined to a wheelchair and had difficulty using his hands and in speaking. Y.H. also experienced damage to structures and areas of the brain involved in sleep.

On his first night in the sleep laboratory, Y.H.’s EEG recordings indicated that his sleep cycle was normal apart from the absence of REM sleep. The complete absence of REM sleep is extremely rare. It is sometimes seen in people who take a high dose of antidepressants or tranquillisers to assist sleeping, as well as in people who are under the influence of hard drugs such as heroin or cocaine. However, Y.H. was not taking medication or other drugs and he did not suffer from depression. When he awoke, he reported that he had slept well and normally.

EEG recordings of Y.H.’s second night again revealed that he had not experienced any REM sleep. Researchers compared Y.H.’s failure to experience REM sleep to that of a person without a heartbeat. Because Y.H. was such a unique case, the researchers asked him to spend an additional six nights in the sleep laboratory so they could further monitor his sleep patterns. Y.H. agreed to this, as well as to further diagnostic testing using brain scanning techniques to confirm the precise location

of the shrapnel that was lodged in his brain. CAT scans showed that, apart from the shell splinters that were lodged in the left hemisphere of the cerebral cortex, there was an additional, previously undetected shrapnel splinter located in the pons at the base of the brain. The pons is the brain mechanism that is believed to control the activation of REM sleep.

Over the next six nights, although some traces of REM sleep were identified on a few nights, on each occasion the amount of REM did not exceed 2–5% of his total sleep. In healthy people of the same age, REM accounts for 20–23% of total sleep. The researchers concluded that Y.H.’s troubled awakenings during the night were not the result of nightmares (which occur in REM sleep), but night terrors that are characteristic of deep NREM sleep. The results of eight nights of testing in the sleep laboratory further showed that Y.H. slept for only 4.5 to 5 hours per night, but he appeared to show no ill-effects throughout the day from this apparent lack of sleep.

The case of Y.H. has been of considerable interest to sleep researchers. When people with healthy, intact brains are deprived of REM sleep, they typically increase their amount of REM sleep when they are allowed to sleep uninterrupted. This is called REM rebound and relates to an apparent need to catch up on missed REM sleep. So, how could someone with such limited amounts of REM sleep show no REM rebound or any side effects? Y.H.’s experiences suggest that the answer probably has something to do with the role of the pons, but exactly why and how damage to the pons affects REM sleep requires further research.

Case study: the man without REM sleep

Source: adapted from Lavie, P. (1996). The enchanted world of sleep.New Haven: Yale University Press


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