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Copyright © 2007 by Allyn and Bacon
Chapter 12 Sleep, Dreaming and Circadian Rhythms
How Much Do You Need to Sleep?
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Copyright © 2007 by Allyn and Bacon
How much sleep do we need?
The amount of time spent sleeping suggests that sleep has a significant biological function
What is that function? What brain mechanisms control
sleep? How does sleep deprivation impact
functioning?
Copyright © 2007 by Allyn and Bacon
3 Physiological Measures of Sleep
Electroencephalogram (EEG)“brain waves”
Electrooculogram (EOG)Eye movements seen during rapid eye
movement (REM) sleep Electromyogram (EMG)
Loss of activity in neck muscles during some sleep stages
Copyright © 2007 by Allyn and Bacon
4 Stages of Sleep EEG
Alpha waves – still awakeBursts of 8- to 12-Hz EEG wavesEyes closed, preparing to sleep
Stage 1similar to awake EEG, but slowerlow-voltage, high-frequency
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Stages of Sleep EEG
EEG voltage increases and frequency decreases as one progresses from stage 1 through 2, 3, and 4
Stage 2 – characterized byK complexes – large negative wavesSleep spindles – burst of 12-14 Hz waves
Stages 3 and 4 – delta waves, large and slow
Copyright © 2007 by Allyn and Bacon
Copyright © 2007 by Allyn and Bacon
Stages of Sleep EEG
Progress to stage 4 sleep and then retreat to stage 1
Emergent stage 1 differs from initial stage 1 REMs Loss of body core muscle tone
Progress through sleep stages in 90 minute cycles
More time spent in emergent stage 1 as night progresses
Copyright © 2007 by Allyn and Bacon
Copyright © 2007 by Allyn and Bacon
Stages of EEG Sleep
Emergent stage 1 sleep = REM sleepNon-REM (NREM) sleep = all other stages
Stage 3 + 4 = slow-wave sleep (SWS) During REM: REMs, loss of core muscle
tone, low-amplitude/high-frequency EEG, increased cerebral and autonomic activity, muscles may twitch, clitoral or penile erection
Copyright © 2007 by Allyn and Bacon
REM Sleep and Dreaming
80% of awakenings from REM yield reports of story-like dreams
External stimuli may be incorporated into dreams
Dreams run on real time Everyone dreams Penile erections are not a result of erotic dreams Sleepwalking and talking are less likely to occur
while dreaming
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Interpretation of Dreams
Freud thought dreams were triggered by unacceptable repressed wishes
Manifest dreams – what we experience
Latent dreams – the underlying meaning
No evidence for this
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Why do we dream?
Freudian theory of dreams Activation-synthesis theory
Cortex creates a story in an effort to make sense of the brain’s activity
Story is synthesized as a consequence of brain activity
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Why do we sleep?
Recuperation theories Sleep is needed to restore homeostasis Wakefulness causes a deviation from homeostasis
Circadian theories Sleep is the result of an internal timing mechanism Sleep evolved to protect us from the dangers of the
night
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Comparative Analysis of Sleep
All mammals and birds do it – must have an important function
Not a special higher-order human function Not necessarily needed in large quantities No clear relationship between species’
sleep time and activity level
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Circadian Sleep Cycles
Circadian rhythms – about a day Virtually all physiological, biochemical,
and behavioral processes show some circadian rhythmicity
Zeitgebers – environmental cues that entrain circadian cycles
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Free-Running Cycles
Remove zeitgebers – still see circadian sleep-wake cycles?
Free-running periods vary, but are usually constant within a subject
Most are longer than 24 hours - ~ 25 What happens on days when you
don’t need to get up?
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Jet Lag and Shift Work
Jet lag – zeitgebers are accelerated or decelerated
Shift work – zeitgebers unchanged, but sleep-wake cycle must be altered
Both produce a variety of deficits Can the effects be prevented or
minimized?
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Reducing Jet Lag
Gradually shift sleep-wake cycle prior to travel
Administer post-flight treatments to promote the needed shiftPhase advance following east-bound travel
with intense light early in the morningHamster studies suggest a good early
morning workout may also help
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Reducing the Effect of Shift Changes Schedule phase delays, rather than phase
advancesMove from current schedule to one that starts
later It is easier to stay up later and get up later
than to retire and arise earlier Phase advances are harder, explaining
why east-bound travel tends to be more problematic
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Effects of Sleep Deprivation
Recuperation theories predict:Long periods of wakefulness will result in
disturbancesDisturbances will get worse as deprivation
continuesAfter deprivation, much of the missed sleep
will be regained What does the research indicate?
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Effects of Sleep Deprivation
How do you separate the effects of stressors used to prevent sleep from the effects of lost sleep?
Does sleep loss affect your performance? We tend to be poor judges of the effects of
sleep deprivation on our performance
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Studies of Sleep Deprivation in Humans 3-4 hours of deprivation in one night
Increased sleepiness Disturbances displayed on written tests of mood Perform poorly on tests of vigilance
2-3 days of continuous deprivation Experience microsleeps, naps of 2-3 seconds
Effects on complex cognitive function, motor performance, and physiological function are less consistent
Copyright © 2007 by Allyn and Bacon
Sleep-Deprivation Studies with Lab Animals Carousel apparatus used to deprive rats of sleep
When the experimental rat’s EEG indicates sleep, the chamber floor moves – if the rat does not awaken, it falls into water
Yoked controls – subjected to the same floor rotations Experimental rats typically die after several days Postmortem studies reveal the extreme stress
experienced by the experimental rats
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REM-Sleep Deprivation
2 consistent effectsProceed more rapidly into REM as REM
deprivation increasesREM rebound – more time spent in
REM when deprivation is over REM rebound suggests that REM
sleep serves a special function
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Purpose of REM?
Necessary for mental health Inconsistent with the effects of tricyclic
antidepressants – block REM Necessary for maintenance of normal
levels of motivation Necessary for processing of memories No clear purpose
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Default Theory of REM
REM serves no critical function One can’t stay continuously in non-REM
sleep, so we switch between REM and wakefulness
When bodily needs exist – wake up No immediate needs – REM No REM rebound seen when lost REM
periods replaced with 15-mins awake
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Sleep Deprivation Increases Sleep Efficiency After sleep deprivation, most of lost stage 4 is
regained and SWS is increased Short sleepers get as much SWS as long
sleepers Naps without SWS do not decrease the night’s
sleep Gradual reductions in sleep time lead to
decreases in stages 1 and 2 Little sleepiness produced with repeated REM
wakenings
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Hypothalamus and Sleep
During WWI – victims of encephalitis lethargica caused some to sleep continuously and others to sleep little
Damage in posterior hypothalamus and adjacent midbrain > excessive sleep
Damage in preoptic area and adjacent forebrain > wakefulness
Copyright © 2007 by Allyn and Bacon
Copyright © 2007 by Allyn and Bacon
Cerveau Isole Preparation
“isolated forebrain” produced by severing cat brain stems between the inferior and superior colliculi
Cortical EEG indicated continuous SWS A cut caudal to this produced the
encephale isole preparation – normal sleep cycle
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Reticular Formation
Something between the cuts producing the cerveau and encpehale isole preparations maintains wakefulness – the reticular formationLeave intact, little effect on cortical EEGStimulation leads to wakefulness
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Reticular REM-sleep Nuclei
Similarities between REM and wakefulness suggest that the same brain area might be involved in both
REM sleep is controlled by nuclei in the caudal reticular formation, each controlling a different aspect of REM
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Suprachiasmatic Nucleus (SCN) of the Medial Hypothalamus Location of the major circadian clocks Lesions do not reduce sleep time, but they
abolish its circadian periodicity Exhibit activity that can be entrained by
the light-dark cycle Transplant SCN, transplant sleep-wake
cycle Other circadian timing mechanisms exist
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Evidence of Other Clocks
Some circadian rhythms intact after SCN lesion
SCN lesions do not eliminate the ability of all environmental stimuli (such as food or water availability) to entrain circadian rhythms
Cells in other parts of the body exhibit free-running circadian rhythms
Copyright © 2007 by Allyn and Bacon
Hypnotic Drugs
Increase sleep Benzodiazepines – Valium, Librium Most commonly prescribed hypnotic Effective in the short-term Complications – tolerance, cessation
leads to insomnia, “addictive”, increase stage 2 while decreasing 4 and REM
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Antihypnotic Drugs
Decrease sleep Stimulants and tricyclic
antidepressantsBoth increase activity of catecholamines
Act preferentially on REM – may totally suppress REM with little effect on total sleep time
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Melatonin
A hormone synthesized from serotonin in the pineal gland
Melatonin levels display circadian rhythms controlled by the SCN
Pineal involved in timing of sexual maturity – function after this is not clear
Melatonin is not a sleep aid, but may be used to shift circadian rhythms
Copyright © 2007 by Allyn and Bacon
Sleep Disorders
Insomnia – disorders of sleep initiation and maintenance
Hypersomnia – disorders of excessive sleep or sleepiness
REM-sleep dysfunctions ~30% of respondents report sleep-related
problems - far fewer truly have a problem
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Insomnia
Iatrogenic – physician createdConsequence of sleeping pill use, for example
Sleep apnea – stop breathing during the night leads to repeated wakenings – 2 typesCaused by muscle spasms or atoniaFailure of the CNS to stimulate breathingMost commonly seen in males, the
overweight, and in the elderly
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Insomnia
Nocturnal myoclonus – twitching of the body, usually the legs, during sleep – most are not aware of why they don’t feel rested
Restless legs – sufferers complain of uneasiness in legs that prevents sleep
Both are often treated with benzodiazepines
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Hypersomnia - Narcolepsy
Severe daytime sleepiness and repeated brief daytime sleeping - “sleep attacks”
Cataplexy – loss of muscle tone while awake
Sleep paralysis – paralyzed while falling asleep or upon waking
Hypnagogic hallucinations – dreaming while awake
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Hypersomnia - Narcolepsy
Appears to be an abnormality in the mechanisms that triggers REMNarcoleptics enter directly into REMDreaming and loss of muscle tone while
awake – suggest REM intruding into wakefulness
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REM-Sleep-Related Disorders
Narcolepsy (also a form of hypersomnia)
REM without atonia – able to act out dreams – possibly caused by damage to the nucleus magnocellularis or its output
Copyright © 2007 by Allyn and Bacon
Effects of Long-Term Sleep Reduction The brain is adaptable – may be able to
function well with very little sleep One deficit seen with subjects sleeping
only 5.5 hours for 60 daysSlight deficit in a test of auditory vigilance
Other study – no ill effects seen at I year with subjects sleeping 7-18 hours less per week than before study
Copyright © 2007 by Allyn and Bacon
How much sleep do you need?
Can this question be answered? Why or why not?