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CHAPTER 15
Sleep and
Consciousness
Sleep and Dreaming
Why do we sleep?
• Why do we sleep?
– Long unanswered question
– We know consequences of NOT sleeping, but not undestand why
we must sleep
• Two major theories regarding function of sleep
– Restorative hypothesis
• species with higher metabolic rates typically spend more time in sleep
• sleep is restorative.
– Adaptive hypothesis
• Less obvious but alternative hypothesis.
• amount of sleep an animal engages in depends
– availability of food
– safety considerations
– low predator vulnerability = greater sleep time
Observations support the hypothesis that sleep is an adaptive response to
feeding and safety needs
Sleep deprivation effects
• Profound effects observed in shift workers:
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Those who work nights
Particularly grave yard shift
Typically sleep less than day shift workers
Fail to adjust sleep-wake cycle adequately
• 5 days a week have reverse day/night cycle
• Weekends revert back to regular hours
• Result: disrupts natural biological or circadian rhythm
• Effects include:
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Poorer work performance
Higher likelihood of accidents
Poorer cognitive function
Higher stress levels
Importance of
biological rhythm
• Circadian rhythm:
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Rhythm or cycle that is about a day in length.
Circa = about
Dia = day
A little longer- about 25 hours long
• Suprachiasmatic nucleus (SCN) of the hypothalamus:
– The main brain area that appears to function as biological clock
– Controls these rhythms in mammals
– Lesioning SCN in rats abolishes normal 24-hour rhythms of sleep,
activity, body temperature, drinking, and steroid secretion.
– Functions as pacemaker: keeps time and regulates activity of
other cells
The nuclei, indicated by the arrows, took up more radioactive 2-deoxyglucose in the scan on the left because the rat was injected during the
day; the rat on the right was injected at night.
Importance of
biological rhythm
• The SCN is entrained to the solar day by
cues called zeitgebers (“time-givers”).
• Differences in light intensity across day
serve as cues to the brain
• Several studies highlight how this works
Importance of
biological rhythm
• SCN relies on light discrepancy to detect day/night
• If place 3rd shift workers in light settings that mimic
opposite day/night cycle, deleterious effects of 3rd shift
disappear
• Antarctic workers in Antarctic winter: moved to natural
25-hour day
• Phase delays show easier to “go to bed later” than
“go to bed earlier”
– Explains why easier to travel west than travel east
– More jet lag when going East!
SCN function
• The SCN regulates pineal gland’s secretion of
melatonin
• Melatonin = hormone that helps induces
sleepiness
• Light resets the biological clock by suppressing
melatonin secretion
– Melatonin often used to combat jet lag
– Also used to treat insomnia in shift workers
and in individuals who are blind.
SCN function
• Light information reaches SCN via direct connection
from retinas: retinohypothalamic pathway.
• Ganglion cells in retina contain melanopsin: lightsensitive substance, or photopigment.
• Melanopsin located in widely branching dendrites
– Helps cells in detecting overall level of light
– NOT contribute to image formation
– ONLY for controlling circadian rhythm.
Important sub-rhythms
• Ultradian rhythms
– rhythms that are shorter than a day in length.
– are shorter than a day in length.
– Important for controlling
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Hormone production
urinary output
Alertness
And other functions which follow regular cycles throughout day.
• Basic Rest and activity cycle
– 90-100 min periods throughout day
– Alertness waxes and wans; particularly in wee morning hours and
late afternoon
EEG patterns:
• EEG: Electroencephalogram can be used to diurnal patterns
• Awake patterns: Alpha and Beta Waves:
– when a person is awake
– alpha waves at 8-12 hertz (Hz): associated with relaxation
– Beta waves: 13-30 Hz. with lower amplitude: associated with
alertness, arousal
• Why lower amplitude with awakefulness/alertness?
– EEG = sum of all electrical potentials
– When relaxed/asleep: firing rhythmical, symmetrical,thus
increases amplitude
– When awake: firing less rhythmical, less symmetrical, varies
as respond to incoming stimuli- this reduces amplitude
EEG Sleep patterns: Stage 1
• Stage 1 sleep: shifts to theta waves
– 4-7 HZ or cycles
– stage between wakefulness and sleep,
– somnolence or drowsy sleep,
– muscles are still quite active
– eyes roll around slowly and may open and close
from time to time.
• Period of transition from unsynchronized beta and
gamma brain waves to more synchronized but
slower alpha waves theta waves
EEG Sleep patterns: Stage 1
• Difficult to pinpoint the actual point of sleep onset (falling asleep):
process is a continuum as brain wave activity gradually slows down.
• Breathing gradually becomes more regular and the heart rate begins
to slow.
• May get sudden twitches or hypnic (hypnagogic) jerks (sudden short
micro-awakenings often accompanied by a falling sensation)
• Sleep may be easily disrupted and sleeper may be aware of sounds
and conversations, but feels unwilling, rather than unable, to respond
to them.
• A person awakened during this period will often believe they have
never slept at all.
• Typically, this stage represents only about 5% of the total sleep time.
EEG Sleep patterns: Stage 2
• Stage 2 sleep: Begins about 10 minutes after Sleep
– first unequivocal stage of sleep,
– muscle activity decreases
– conscious awareness of the outside world begins to
fade completely.
– If any sounds are heard, the sleeper not able to
understand content at this point.
• Theta waves and 2 other forms of brain activity:
– Sleep spindles: brief bursts of 12- to 14-Hz waves that
last about a half second
– K complexes: sharp, large waves that occur
approximately once per minute and last about a
minute.
EEG Sleep patterns: Stage 2
• Sleep spindles and K complexes:.
– Serve to protect sleep and suppress response to
outside stimuli
– Also aid in sleep-based memory consolidation and
information processing.
• Because sleepers pass though this stage several
times during the night, more time is spent in stage 2
sleep than in any other single stage,
• Typically constitutes about 45%-50% of total sleep
time for adults (or even more in young adults).
EEG Sleep patterns: Stage 3
• Stage 3 (NREM3 or N3) :
– Deep or delta or slow-wave sleep (SWS),
– Sleeper is not responsive to the outside
environment,
• essentially cut off from the world
• unaware of any sounds or other stimuli.
• Stage 3 sleep occurs in longer periods during
the first half of the night, particularly during the
first two sleep cycles
– Represents around 15%-20% of total adult sleep
time.
EEG Sleep patterns: Stage 3
• Stage 3 (following the guidelines of the American
Academy of Sleep Medicine) was split into two stages
– Stage 3 and stage 4,
– Depended on the frequency of delta waves (stage 4 was
initially defined as when delta waves exceeded 50% of the
total).
• Other physical indicators of stage 3 sleep: lowest levels for
– brain temperature,
– breathing rate,
– heart rate and b
• Dreaming is more common during this stage than in the
other non-REM sleep stages, although not as common as
during REM sleep.
EEG Sleep patterns: Stage 3
• This is stage during which parasomnias like night terrors, sleepwalking, sleep-talking and bedwetting occur.
• Information processing and memory consolidation (particularly of the
declarative memory) also takes place during this period,
– Also some consolidation during the stage 2 and REM stages.
• It is much more difficult to wake a person during stage 3 sleep
• If awakened at this stage they will often feel very groggy and may take
up to 30 minutes before they attain normal mental performance
(known as sleep inertia).
• Children and young adults tend to have more slow-wave stage 3 sleep
than adults, and the elderly may experience little or no stage 3 sleep at
all.
REM Sleep
• REM sleep: Rapid Eye movement Sleep
– Occurs in cycles of about 90-120 minutes throughout the
night,
– Accounts for up to 20-25% of total sleep time in adult
humans,
• proportion decreases with age
• newborn baby may spend 80% of total sleep time in the
REM stage; older adult much less
• REM sleep dominates the latter half of the sleep period,
– Especially the hours before waking
– REM component of each sleep cycle typically increases as
the night goes on.
REM Sleep
• Associated with rapid (and apparently random) side-to-side
movements of the closed eyes
– can be monitored and measured by a technique called
electrooculography (EOG).
– Eye motion is not constant (tonic) but intermittent
(phasic).
• Still not known exactly what purpose it serves, but it is
believed that the eye movements may relate to the internal
visual images of the dreams that occur during REM sleep,
– Seem to be associated with brain wave spikes in the
regions of the brain involved with vision (as well as
elsewhere in the cerebral cortex).
REM Sleep
• Brain activity during REM sleep is largely characterized by
low-amplitude mixed-frequency brain waves
– Very similar to those experienced during the waking state theta waves, alpha waves and even the high frequency
beta waves more typical of high-level active concentration
and thinking.
– Show up as the typical “saw-tooth” brain wave pattern on
an electroencephalogram (EEG)
– REM sleep also called “paradoxical sleep” because brain
waves are similar to the awake state
• Brain’s oxygen and energy consumption very high during
REM sleep
– Often higher than when awake and working on a complex
problem.
REM Sleep
• Breathing becomes more rapid and irregular during REM sleep
than during non-REM sleep
• Heart rate and blood pressure also increase to near waking
levels.
• Core temperature is not well regulated during REM sleep
– Tends towards the ambient temperature
– Similar to how reptiles and other cold-blooded animals
maintain their temp regulation
• Sexual arousal is common during REM sleep
– Male and female may both become aroused and penis stays
erect for substantial periods during this sleep stage,
– Occurs regardless of whether or not any dreams in progress
are of an erotic nature.
REM Sleep
• Muscles become completely paralyzed and
unresponsive during REM sleep.
– Atonia: absence of muscle tone and skeletal
muscle activity
– Occurs because the brain impulses that control
muscle movement are completely suppressed
(except for life sustaining functions)
• Locus coeruleus: Part of the Pons
– Source of these inhibitory signals
– Utilize the neurotransmitter norepinephrine
REM Sleep
• The majority of dreams - certainly the most memorable and
vivid dreams - occur during REM sleep
– Muscular atonia during REM may be a built-in measure to protect us
from self-damage which could occur while physically acting out these
vivid REM dreams.
– Support for this hypothesis: Michel Jouvet’s early experiments on cats
• Muscle inhibition nerves were severed,
• Led to cats to physically stalk invisible prey and runing and jumping
around around wildly during the dreams of REM sleep.
• Neurologically, REM sleep activated by secretion of the
neurotransmitter acetylcholine
– Inhibited by the neurotransmitter serotonin
– Principally generated in the pons region of the brainstem.
– Animal research shows that surgical destruction of locus
corealus can eliminate REM sleep
REM Sleep;
Memory functions
• Brain areas involved with long-term memory and emotion are very
active during REM sleep
– Lack of REM sleep impairs the ability to learn complex tasks
• Suggests that REM sleep is a vital for sleep cycle
– Particularly during early childhood development (more REM
sleep)
– If REM sleep is repeatedly interrupted/shortened: longer REM
“rebound sleep” tends to occur at the next opportunity in
compensation (skip past early stages)
• Some memory consolidation during REM sleep
– Particularly of procedural and spatial memory
– Not to the same extent as during the later stages of non-REM
– Spend more time in REM sleep following days when have been
in unusual situations requiring learning a lot of new tasks.
REM Sleep;
Memory functions
• Most people do not tend to wake after each cycle of REM sleep
• More likely to wake after REM than other stages
• “Micro-awakenings” = few seconds only,
– Sleeper does not normally remember them.
– If over-stimulated, may wake up fully, and may take the length of an
entire sleep cycle (1.5 - 2 hours) to get back to sleep.
• Always assumed that REM sleep (and dreams) = physiological
necessity,
– Now this is being questioned.
– Dreaming seems to move to non-REM sleep stages
– Animals deprived of REM sleep for as long as two months seem to be
able to continue with very little perceptible behavioural or physiological
injury
– Humans taking certain antidepressant medications that result in little or
no REM sleep appear to show few negative consequences.
Function of Rem Sleep
• Activation-synthesis hypothesis,
– During REM sleep : forebrain integrates neural activity
generated by brain stem with information stored in memory.
– Brain uses information from memory to impose meaning on
nonsensical random input.
• Biological hypothesis: REM sleep promotes neural development
during childhood.
– Excitation that spreads through the brain from the pons during
REM sleep encourages differentiation
– Also encourages maturation
– As well as myelination in higher brain centers.
Theories of non-REM Sleep
• Early theories of non-REM functions
– Focused on rest and restoration: early data showed slow wave sleep
increases following exercise.
– More current data suggests these changes may be due to overheating
rather than fatigue.
– Horne (1988): slow wave sleep more related to increased temperature
of brain than increase in body temperature.
• Horne (1992): slow wave sleep promotes cerebral recovery
– especially in the prefrontal cortex.
– Important areas for memory, consolidation
Function of non-rem sleep
• Ribeiro, et al., (2004): Neuronal replay strongest during nonREM sleep
– Recall, amplification of hippocampal activity that occurs during learning
– Replaying or rehearsing and consolidating.
– During REM, hippocampus up-regulates genes in cortex that involved in
synaptic plasticity
– Implements transfer of memory from hippocampus to cortex.
• Crick and Mitchison’s (1995) Reverse learning hypothesis
– REM is also a period of memory erasure.
– Neural networks involved in memory must purge themselves of erroneous
connections
– Simulation data show enhanced performance of computer neural networks
with reverse learning,
– Mammals without REM sleep have large brains for their body size-can’t
undo learning as well.
Sleep as
homeostatic function
• Sleep is homeostatic:
– period of deprivation followed by a lengthened sleep period
– Sleep disruptions followed by behavioral attempts to rectify
sleep cycle
• Adenosine provides at least one of mechanisms of
sleep homeostasis.
– During wakefulness: Adenosine accumulates in basal
forebrain area.
– inhibits arousal-producing neurons there
– Result: drowsiness and reduced EEG activation.
Sleep as
homeostatic function
• Adenosine also active in preoptic area of the
hypothalamus (POA).
– Warming POA of hypothalamus activates sleep-related
cells
– Warming inhibits waking-related cells in the basal
forebrain
– Warming enhances slow-wave EEG.
• Neurons in Ventrolateral preoptic nucleus (VPN)
double rate of firing during sleep: function =
inhibit neurons in arousal areas
Two arousal pathways
• Pedunculopontine and laterodorsal tegmental nuclei
(PPT/LDT)
– Neurons from the PPT/LDT activate areas crucial for transmission to the
cortex
– Also desynchronize the EEG;
– active during REM sleep.
• Arousing pathway
– activates the cortex
– facilitates the processing of inputs from the thalamus.
– completed by neurons from lateral hypothalamus.
Arousing pathway
• Arousal involves selective activity in LH
neurons
– Lateral hypothalamus neurons release
either
•Hypocretin:
– most active during waking
– Acts on part of arousing pathway
•Melanocortin or melanocortinconcentrating hormone:
– most active during REM Sleep
– Acts on part of PPT/LPT pathway
Arousing pathway
• LH neurons send hypocretin-releasing
hormone to other arousal centers
including:
– Basal forbrain area; tumeromammillary nucleus,
– PPT/LDT
– raphe nuclei and locus coeruleus
• Help keep waking centers active
– Not sure if initiates waking or maintains
it; may prevent unintentional “switching”
Arousing pathway
• Sleep medications can alter state of consciousness by altering
function of the LH neurons
• Antihistamines:
– pass through blood brain barrier
– block histamine receptors in LH/arousal pathway
• Other agents enhance GABA activity in LH/arousal pathway-inhibitory
– Barbituates:
– benzodiazepines,
– Alcohol
– most gaseous anesthetics
Sleep and Dreaming:
PGO waves
• Ponto-geniculo-occipital waves or PGO waves:
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Phasic field potentials which can be recorded from:
Begin as electrical pulses from the pons
Then move to LGN
Finally end up in primary visual cortex
Waveforms originate in these areas
• Appearances of PGO waves are most prominent in right before REM
– May be intricately involved with eye movement of wake AND sleep cycles
• Arousal by PGO waves may account for EEG desynchrony and visual
imagery observed during REM sleep.
(a) Activity in the locus coeruleus;
(b) (b) activity in the raphe nuclei.
AW, alert waking; QW, quiet waking; DRO, drowsy; SWS, slow wave sleep; Pre
REM, 60 seconds before REM; Post REM, first second after REM ends.
Take home lesson
• Why do we sleep?
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Restorative: allows us to restore our bodies
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Especially our brain
Memory consolidation
Memory deletion: dump unnecessary stuff
• Amount you sleep varies over life cycle
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More when younger; less as age
More to learn when younger!
• Many brain areas involved in sleep; most are in the brain
stem.
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Disruptions in sleep can have behavioral effects
Can potentially result in death- although rarely