Week 7 textbook notes - SLEEP, DREAMING AND CIRCADIAN RHYTHMS. PDF

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Textbook notes - SLEEP, DREAMING AND CIRCADIAN RHYTHMS....

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WEEK 7: SLEEP, DREAMING AND CIRCADIAN RHYTHMS. A. I.    II. 

Stages of Sleep Three standard psychophysiological measures of sleep. The electroencephalogram (EEG) The electrooculogram (EOG) The neck electromyogram (EMG) Three stages of sleep EEG. After the eyes are shut and a person prepares to go to sleep, alpha waves – waxing and waning bursts of 8to 12-Hz EEG waves – begin to punctuate the low-voltage, high-frequency waves of alert wakefulness  Then, as the person falls asleep, there is a sudden transition to a period of stage 1 sleep EEG. 1. Stage 1 – NREM 1 (N1)  The stage 1 sleep EEG is a low-voltage, high-frequency signal that is similar to, but slower than, that of alert wakefulness. 2. Stage 2 – NREM 2 (N2)  The stage 2 sleep EEG has a slightly higher amplitude and a lower frequency than the stage 1 EEG.  It is punctuated by 2 characteristics wave forms: o K complexes: each K complex is a single large negative wave (upward deflection) followed immediately by a single large positive wave (downward reflection) o Sleep spindles: each sleep spindle is a 0.5 to 3 seconds waxing and warning burst of 9 to 15 Hz waves. 3. Stage 3 – NREM 3 (N3) – often referred to as slow-wave sleep (SWS)  Once sleepers reach stage 3 EEG sleep, they stay there for a time, and then they retreat back through the stages of sleep to stage 1.  However, when they return to stage 1, things are not at all the same as they were the first time through.  The first period of stage 1 EED during a night’s sleep ( initial stage 1 EEG) is not marked by any striking electromyographic or electrooculographic changes, whereas subsequent periods of stage 1 sleep EEG (emergent stage 1 EEG – often called REM sleep) are accompanied by REMs and by a loss of tone in the muscles of the body core. 

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After the first cycle of sleep EEG – from initial stage 1 to stage 3 and back to emergent stage 1 – the rest of the night is spent going back and forth through the stages Each cycle tends to be about 90 minutes long o More and more time is spent in emergent stage 1 sleep o Less and less time is spent in the other stages, particularly stage 3.

REMs, loss of core-muscle tone, and a low-amplitude, highfrequency EEG are not the only physiological correlates of REM sleep.  Cerebral activity (e.g., oxygen consumption, blood flow, and neural firing) increases to waking levels in many brain structures, and there is a general increase in the variability of autonomic nervous system activity (e.g., in blood pressure, pulse, and respiration).  Also, the muscles of the extremities occasionally twitch, and there is almost always some degree of penile or clitoral erection. III. Dreaming 1. REM sleep and dreaming.  REM sleep episodes were emotion-charged.  The physiological correlate of dreaming came from the observation that o 80% of awakenings from REM sleep o But only 7% of awakenings from NREM sleep, led to dream recall  The dreams recalled from NREM sleep tended to be isolated experiences (e.g., “I was falling”)

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Those associated with REM sleep tended to take the form of stories or narratives. More problematic is that REM sleep and dreaming can be dissociated. o For example, antidepressants greatly reduce or abolish REM sleep without affecting aspects of dream recall o Conversely, cortical lesions can abolish dreaming without affecting REM sleep. 2. Testing common beliefs about dreaming (5 beliefs)  External stimuli can become incorporated into their dreams. o Dement and Wolpert (1958) sprayed water on sleeping volunteers after they had been in REM sleep for a few minutes and then awakened them a few seconds later. o In 14 of 33 cases, the water was incorporated into the dream report.  Some people believe dreams last only an instant, but research suggests that dreams run on “real time” o Volunteers were awakened 5 or 15 minutes after the beginning of a REM episode and asked to decide on the basis of the duration of the events in their dreams whether they had been drea ming for 5 or 15 mins. o They were correct in 92 of 111 cases.  Some people claim that they do not dream. However, these people have just as much REM sleep as normal dreamers. Moreover, most report dreams if they are awakened during REM episodes, although they do so less frequently than do normal dreams  Penile erection are commonly assumed to be indicative of dreams with sexual content. However, erections are no more complete during dreams with frank sexual content that during those without it.  Many people believe sleeptalking (somniloquy) and sleepwalking (somnambulism) occur during REM sleep. This is not so. o Sleepingtalking has no special association with REM sleep – it can occur during any stage but often occurs during the transition to wakefulness. o Sleepwalking usually occurs during slow-wave sleep, and it never occurs during REM sleep, when core muscles tend to be totally relaxed. 3. Interpretation of dreams.  Freud believe that dreams are triggered by unacceptable repressed wishes, often of a sexual nature.  Because dreams represent unacceptable wishes, the dreams we experience (our manifest dreams) are merely disguised versions of our real dreams (our latent dreams).  Therefore, one of the keys to understanding people and dealing with their psychological problems is to expose the meaning of their latent dreams through the interpretation of their manifest dreams.  One widely held alternative to the Freudian theory of dreams is Hobson’s (1989) activation-synthesis hypothesis: during REM sleep, many brain-stem circuits become active and bombard the cerebral cortex with neural signals.  The essence of activation-synthesis hypothesis is: the cortex’s effort to make sense of these random signals. o That’s why we might liken this process to what happens when you stare up at the clouds and happen to see faces and figures among them: the clouds are randomly patterned, but our brain is trying its best to make sense of that random patterns. B. Why do we sleep, and why do we sleep when we do? 1. 2 kinds of theories of sleep.  Recuperation theories: being awake disrupts the homeostasis (internal physiological stability) of the body in some way and sleep is required to store it. o Various recuperation theories differ in terms of the particular physiological disruption the propose as the trigger for sleep. o For example, the 2 most common recuperation theories of sleep are the function of sleep is to:  1. Restore energy levels that decline during wakefulness,  2. Clear toxins (e.g, beta-amyloid) from the brain and other tissues that accumulate during wakefulness.  Regardless 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 that sleep is terminated by a return to homeostasis.

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Adaptation theories: sleep is not a reaction to the disruptive effects of being awake but the result of an internal 24-hour timing mechanism – that is, we humans are programmed to sleep at night regardless of what happens to us during the day o Focus more on when we sleep than on the function of sleep. o According to these theories, early humans had enough time to get their eating, drinking, and reproducing out of the way during the daytime, and their strong motivation to sleep at night evolved to conserve their energy resources and to make them less susceptible to mishap (e.g., predation) in the dark. o Adaption theories suggest that sleep is like reproductive behaviour in the sense that we are highly motivated to engage in it, but we don’t need it to stay health 2. Comparative analysis of sleep.  First, sleep serves some important physiological function, rather than merely protecting animals from mishap and conserving energy.  Second, the primary function of sleep is not some special, higher-order human function. o For example, sleep helps humans reprogram our complex brains or that is permits some kind of emotional release to maintain our mental health are improbable in view of the comparative evidence.  Third, although sleep may be essential for survival, it is not necessarily needed in large quantities.  Fourth, reasons why some species are long sleepers and others are short sleepers. o Energy-related factors. However, there is no strong relationship between species’ sleep time and its level of activity, its body size and temperature. o Adaption theories: the daily sleep time of each species is related to how vulnerable it is while it is asleep and how much time it must spend each day to feed itself and to take care of its other survival requirements.  For example, African lions often sleep more or less continuously for 2 or 3 days after they have gorged themselves on a kill. C. Effects of sleep deprivation 1. Predictions of Recuperation theories about sleep deprivation  Three predictions: o Long periods of wakefulness will produce physiological and behavioural disturbances. o These disturbances will grow worse as the sleep deprivation continues. o After a period of deprivation has ended, much of the missed sleep will be regained. 2. Two classic Sleep-deprivation case studies.  The case of the Sleep-Deprived students. o First night: they read or studied with little difficulty until after 3am, when they experienced an attack of sleepiness o Second day: reading or studying was next to impossible because sleepiness was so severe o Third and fourth night: sleepiness resembled that on the second. o Surprisingly, things did not grow worse after the fourth night, and those students who persisted repeatedly went through the same daily cycle  The case of Randy Gardner. o Did not have to sleep longer to “catch up” on his lost sleep....