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Chapter 14

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Department
Psychology
Course
Psychology 2220A/B
Professor
Scott Mac Dougall- Shackleton
Semester
Fall

Description
Chapter 14: Sleep, Dreaming, and Circadian Rhythms STAGES OF SLEEP • Three Standard Psychophysiological Measures of Sleep • Rapid eye movements (REMs) occur under the closed eyelids of sleepers during these periods of low-voltage, fast EEG activity • There is also a loss of electromyographic activity in the neck muscles during these same sleep periods • Subsequently, the electroencephalogram (EEG), the electroculogram (EOG), and the electromyogram (EMG) became the three standard psychophysiological bases for defining stages of sleep • The disturbance of sleep observed during the first night in a sleep laboratory is called the first-night phenomenon • Four Stages of Sleep EEG • There are four stages of sleep EEG: stage 1, stage 2, stage 3, and stage 4 • After the eyes are shut and a person prepares to go to sleep, alpha waves - waxing and waning bursts of 8-12 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 • The stage 1 sleep EEG is a low-voltage, high frequency signal that is similar to, but slower than that of alert wakefulness • There is a gradual increase in EEG voltage and a decrease in EEG frequency as the person progresses from stage 1 sleep through stages 2,3 and 4 • Accordingly, the stage 2 sleep EEG has a slightly higher amplitude and a lower frequency than the stage 1 EEG; in addition it is punctuated by two characteristic wave forms: K complexes and sleep spindles • K complex is a single large negative wave followed immediately by a single large positive wave • Each sleep spindle is a 1-2 second waxing and waning burst of 12-14 Hz waves • The stage 2 sleep EEG is defined by the occasional presence of delta waves - the largest and slowest EEG waves. with a frequency of 1-2 Hz • Stage 4 sleep EEG is defined by a predominance of delta waves • Once sleepers reach stage 4 EEG sleep, they stay there for a time, and then they retreat back through the stages of sleep to stage 1 • When they return to stage 1, things are not at all the same as they were the first time through • The first period of stage 1 EEG during a night’s sleep (initial stage 1 EEG) is not marked by any striking electromyographic or electroculographic changes, whereas subsequent periods of stage 1 sleep EEG (emergent stage 1 EEG) are accompanied by REMs and by a loss of tone in the muscles of the body core • Each cycle tends to be about 90 minutes and that, as the night progresses, more and more time is spent in emergent stage 1 sleep, and less and less time is spent in the other stages, particularly stage 4 • The sleep associated with emergent stage 1 EEG is usually called REM sleep, after the associated rapid eye movements; whereas all other stages of sleep together are called NREM sleep Chapter 14: Sleep, Dreaming, and Circadian Rhythms • Stages 3 and 4 together are referred to as slow-wave sleep (SWS) after the delta waves that characterize them • Cerebral activity increases to waking levels in many brain structures and there is a general increase in the variability of autonomic nervous system activity • REM Sleep and Dreaming • With the exception of the loss of tone in the core muscles. all of the other measures suggested that REM sleep episodes were emotion-charged • Dreams recalled from NREM sleep tended to be isolated experience while those associated with REM sleep tended to take the form of stories or narratives • Testing Common Beliefs and Dreaming • Following five beliefs were addressed: • Many people believe that external stimuli can become incorporated into their dreams • Some people believe that dreams last only an instant. but research suggests that dreams run on “real time” • Some people claim that they do not dream • Penile erections are commonly assumed to be indicative of dreams with sexual content • Many people believe that sleeptalking and sleepwalking occur only during dreaming • Interpretation of Dreams • Freud believed that dreams are triggered by unacceptable repressed wishes often of a sexual nature • Hypothesized an unconscious censor that disguises and subtracts information form our real dreams so that we can endure them • Concluded that one of the keys to understanding people and dealing with their psychological problems is to expose the meaning of their latent dreams through the interpretation of their manifest dreams • Many people accept the notion that dreams bubble up from a troubled subconscious and that they represent repressed thoughts and wishes • Hobson’s theory is based on the observation that, during REM sleep, many brain- stem circuits become active and bombard the cerebral cortex with neural signals • The essence of the activation-synthesis theory is that the information supplied to the cortex during REM sleep is largely random and that the resulting dream is the cortex’s effort to make sense of these random signals WHY DO WE SLEEP, AND WHY DO WE SLEEP WHEN WE DO? • Two kinds f theories for sleep have been proposed: recuperation theories ad adaptation theories • Difference between these two theoretical approaches are revealed by the answers they offer or the two fundamental questions about sleep • Recuperation theories of sleep is that being awake disrupts the homeostasis of the body in some way and sleep is required to restore it • Restoration theories of sleep all imply that sleepiness is triggered by a deviation from homeostasis caused by wakefulness and that sleep is terminated by a return to homeostasis Chapter 14: Sleep, Dreaming, and Circadian Rhythms • The essence of adaptation theories of sleep is that sleep is not a reaction to the disruptive effects of being awake but the result of an internal 24 hour timing mechanism • According to these theories, we have evolved to sleep at night because sleep protects us form accident and predation during the night • Comparative Analysis of Sleep • Evidence suggests that most mammals and birds sleep • The sleep of mammals and birds like our, is characterized by high-amplitude, low frequency EEG waves punctuated by periods of low-amplitude, high frequency waves • Evidence for sleep in amphibians, reptiles, fish, and insects is less clear: some display periods of inactivity and unresponsiveness, but the relation of these periods to mammalian sleep has not been established • The fact that most mammals and bird sleep suggests that sleep serves some important physiological function rather than merely protecting animals form mishap and conserving energy • The evidence is strongest in species that are at increased risk of predation when thy sleep and in species that have evolved complex mechanisms that enable them to sleep • The fact that most mammals and birds sleep suggests that the primary function of sleep is not some special, higher-order human function • The large between-species difference in sleep time suggest that although sleep may be essential for survival, it is necessarily needed in large quantities • Many studies have tried to identify some characteristic that identifies various species as long sleepers or short sleepers • Under the influence of recuperation theories, researchers have focused on energy- related factors in their efforts • However, there is no strong relationship between a species’ sleep time and its level of activity, its body size, or its body temperature EFFECTS OF SLEEP DEPRIVATION • One way to identify the functions of sleep is to determine what happens when a person is deprived of sleep • Interpretation of the Effects of Sleep Deprivation: The Stress Problem • In Western cultures, most people who sleep little or irregularly do so because they are under extreme stress which could have adverse effects independent of any sleep loss • Because it is difficult to separate the effects of sleep loss from the effects of stressful conditions that may have induced the loss, results of sleep deprivation studies must be interpreted with particular caution • Predictions of Recuperation Theories about Sleep Deprivation • Because recuperation theories of sleep are based on the premise that sleep is a response to the accumulation of some debilitating effect of wakefulness, they make the following three predictions about sleep deprivation • Long periods of wakefulness will produce physiological and behavioral disturbances Chapter 14: Sleep, Dreaming, and Circadian Rhythms •These disturbances will grow steadily worse as the sleep deprivation continues •After a period of deprivation has ended, much of the missed sleep will be regained • Experimental Studies of Sleep Deprivation in Humans • Even moderate amounts of sleep deprivation have been found to have three consistent effects •First, sleep-deprived individuals display an increase in sleepiness •Second, sleep-deprived individuals display negative affect on various written tests of mood •Third, they perform poorly on tests of vigilance • The disruptive impact of sleep deprivation on cognitive function has been clarified by the discovery that only some cognitive functions are susceptible • Performance on tests of executive function has proven much more susceptible • The adverse effects of sleep deprivation on physical performance have been surprisingly inconsistent • Sleep deprivation has been found to have a variety of physiological consequences such as reduced body temperature, increases in blood pressure, decreases in some aspects of immune function, hormonal changes and metabolic changes • Little evidence that these changes have any consequences for health or performance • Microsleeps are brief periods of sleep, typically about 2 or 3 seconds long, during which the eyelids droop and the subjects become less responsive to external stimuli, event hough they remain sitting or standing • Useful to compare the effects of sleep deprivation with those of deprivation of the motivated behaviours • Despite our powerful drive to sleep, the effects of sleep deprivation tend to be subtle, selective, and variable • Performance deficits observed after extended periods of sleep deprivation disappear so readily • Sleep-Deprivation Studies with Laboratory Animals • The carousel apparatus has been used to deprivate rats of sleep • The fact that humans and rats have been sleep-deprived by other means for similar periods of time without dire consequences argues for caution in interpreting the results of the carousel sleep-deprivation experiments • It may be that apparatus kills the experimental rats not because it keeps them from sleeping but because it is stressful • REM-Sleep Deprivation • REM-sleep deprivation has been shown to have two consistent effects •First, following REM-sleep deprivation, participants display a REM rebounds that is, they have more than their usual amount of REM sleep for the first two or three nights •Second, with each successive night of deprivation, there is a greater tendency for participants to initiate REM sequences • The compensatory increase in REM sleep following a period of REM-sleep deprivation suggests that the amount of REM sleep is regulated separately from the amount of slow-wave sleep and that REM sleep serves a special function Chapter 14: Sleep, Dreaming, and Circadian Rhythms • Robert Vertes and Jerome Seigel argued that the evidence that REM sleep strengthens memory is unconvincing • They point out that numerous studies fail to support a mnemonic function of REM sleep have been ignored • The default theory of REM sleep is a different approach • According to this theory, it is difficult to stay continuously in NREM sleep, so the brain periodically switches to one of two other states • If there is any immediate bodily need to take care, the brain switches to wakefulness; if there are no immediate needs, it switches to the default state - REM sleep • According to the default theory, REM sleep is more adaptive when there are no immediate bodily needs • Sleep Deprivation Increases the Efficiency of Sleep • Research is that individuals who are deprived of sleep become more efficient sleepers • Their sleep has a higher proportion of slow-wave sleep which seems to serve the main restorative function • Six major pieces of evidence that support it: • Although people regain only small proportion of their total lost sleep after a period of sleep deprivation, they regain most of their lost stage 4 sleep • After sleep deprivation, the slow-wave sleep EEG of humans is characterized by an even higher proportion than usual of slow waves • People who sleep 6 hours or less per night normally get as much slow-wave sleep as people who sleep 8 hours or more • Naptime EEG shows few slow waves, and the nap does not reduce the duration of the following night’s sleep • People who gradually reduce their usual sleep time get less stage 1 and stage 2 sleep, but the duration of their slow-wave sleep remains about the same as before • Repeatedly walking individuals during REM sleep produces little increase in the sleepiness they experience the next day, whereas repeatedly waking individuals during slow-wave sleep has major effects • The negative consequences of sleep loss in inefficient sleepers does not indicate whether the lost sleep was really needed • Only when people are sleeping at their maximum efficiency it is possible to determine how much sleep they really need CIRCADIAN SLEEP CYCLES • Although the sleep-wake cycle is the most obvious circadian rhythm, it is difficult to find a physiological, biochemical, or behavioral process in animals that does not display some measure of circadian rhythmicity • Out circadian cycles are kept on their once every 24 hours schedule by temporal cues in the environment • Environmental cues that can entrain circadian rhythms are called zeitgebers • In a world without 24 hour cycles of light and dark, other zeitgebers can entrain circadian cycles Chapter 14: Sleep, Dreaming, and Circadian Rhythms • Free-Running Circadian Sleep-Wake Cycles • Under conditions in which there are absolutely no temporal cues, humans and other animals maintain all of their circadian rhythms • Circadian rhythms in constant environments are said to be free-running rhythms, and their duration is called the free-running period • Free-running periods vary in length from subject to subject, are of relatively constant duration within a given subject, and are usually longer than 24 hours • The regularity of free-running sleep-wake provides support for the dominance of circadian factors over recuperative factors in the regulation of sleepFree0running circadian cycles do not have to be learned • Many animals display a circadian cycle of body temperature that is related to their circadian sleep-wake cycle • Their sleep-wake and body temperature cycles sometimes break away form one another this is called internal desynchronization The potential for the simultaneous existence of two different free-running periods suggests that there is more than one circadian timing mechanism, and that sleep is not casually related to the decreases in body temperature that are normally associated with it • On occasions when subjects stay awake longer than usual, the following sleep time is shorter rather than longer • Jet Lag and Shift Work • Two different disruptions of circadian rhythmicity: jet lag and shift work • Jet lag occurs when the zeitgebers that control the phases of various circadian rhythms are accelerated during east-bound flights (phase advance) or decelerated (phase delays) • Shift work, the zeitgebers stay the same, but workers are forced to adjust their natural sleep-wake cycles in order to meet the demands of changing work schedules • Both produce sleep disturbances, fatigue, general malaise, and deficits on tests of physical and cognitive function • Two behavioral approaches have been proposed for the reduction of jet lag •One is gradually shifting ones sleep-wake cycle in the days prior to the flight •The other is administering treatments after the flight that promote the required shift in the circadian rhythm • Companies that employ shift workers have had success in improving the productivity and job satisfaction of those workers by scheduling phase delays rather than phase advances • A Circadian Clock in the Suprachiasmatic Nuclei • The fact that circadian sleep
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