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SLEEP AND CONSCIOUSNESS
CHAPTER 15
Sleep and dreaming
The neural basis of consciousness
Sleep and Dreaming
• The Function of Sleep
– The fact that species with higher metabolic rates typically
spend more time in sleep supports the hypothesis that sleep is
restorative.
– The Adaptive Hypothesis.
• The amount of sleep an animal engages in depends on the
availability of food and on safety considerations.
• For example, predators (lions) and animals that can hide
(bats) sleep a lot.
• Vulnerable animals without shelter (cattle) and those that
need to spend hours feeding (elephants) sleep very little.
Time Spent in Sleep for Different Species
Figure 15.1
Sleep and Dreaming
 Performance deficits show the importance of sleep.
– Deprivation Studies
• Performance declines in shift workers.
• In long-term deprivation studies, performance declines at night
and recovers somewhat during the day.
– Night-Time Accidents
• Driving accidents peak at 2 a.m
• The Chernobyl meltdown, the Bhopal chemical plant leakage,
and the Exxon Valdez oil spill occurred in the early morning
hours.
– Traveling eastward across time zones decreases performance.
• For example, west coast teams playing in the east won fewer
games than east coast teams playing in the west.
Sleep and Dreaming
• A circadian rhythm is a rhythm that is about a day
in length.
– The main biological clock in mammals is the
suprachiasmatic nucleus (SCN) of the hypothalamus.
• Lesioning the SCN in rats abolishes the normal 24hour rhythms of sleep, activity, body temperature,
drinking, and steroid secretion.
• The SCN is entrained to the day-night cycle by
zeitgebers (“time-givers”); the most important
zeitgeber is light.
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The Suprachiasmatic Nucleus
Figure 15.2
(a) In the rat, the SCN is active during lights-on (its sleep period),
but (b) not during darkness.
Sleep and Dreaming
• In isolation studies, subjects typically follow a longer
sleep-wake cycle.
– For example, Greenpeace volunteers living in isolation during the 4
months of darkness of the Antarctic winter had a sleep/wake cycle of
approximately 25 hours.
– Some researchers believe the clock is linked to the 24.8-hour lunar
cycle.
– But subject control of room lighting may create an artifact.
• Bright light at the end of the day lengthens the cycle.
• When light was kept too dim to influence the cycle, the sleepwake period averaged 24.18 hours.
Sleep & Wake Periods During Isolation
Figure 15.3
Sleep and Dreaming
 The SCN regulates the pineal gland’s secretion of
melatonin, a hormone that induces sleepiness.
 Melatonin is often used to combat jet lag and to treat insomnia in shift
workers and in the blind.
 Light resets the clock by suppressing melatonin secretion.
 Light information reaches the SCN by way of the
retinohypothalamic pathway.
 Ganglion cells in the retina contain melanopsin, which is a lightsensitive substance, or photopigment.
 This system explains why some blind individuals entrain to light.
Melanopsin in Ganglion Cells
Figure 15.4
The cells were labeled with a fluorescent substance that reacts to melanopsin.
Sleep and Dreaming
• Ultradian rhythms are those that are shorter
than a day in length.
– Hormone production, urinary output, alertness, and other
functions follow regular cycles throughout the day.
– One example of an ultradian rhythm is the basic rest and
activity cycle, which is a rhythm that is about 90-100 minutes
long.
– Alertness, daydreaming, and EEG activity follow this cycle.
– This cycle also extends into sleep, with 90-minute variations in
arousal.
◊
Sleep and Dreaming
 The most important measure of sleep activity is the
electroencephalogram, or EEG.
 When a person is awake, the EEG is a mix of alpha (8-12 Hz) and beta
(13-30 Hz) waves.
 As the person slips into the light first stage of sleep, the EEG shifts to
theta (4-7 Hz) waves.
– About 10 minutes later Stage 2 begins, indicated by:
• sleep spindles, brief bursts of 12- to 14-Hz waves;
• K complexes, sharp, high amplitude waves that occur once a
minute.
 Stages 3 and 4 are known as slow wave sleep and are characterized by
large, slow delta waves at a frequency of 1-3 Hz.
EEG and the Stages of Sleep
Figure 15.5
Sleep and Dreaming
• After stage 4 the sleeper moves rather quickly back
through the stages in reverse order.
• But rather than returning to Stage 1, the sleeper enters
REM sleep.
– REM, or rapid eye movement sleep is so called because the
eyes dart back and forth horizontally during this stage.
– REM sleep increases over the night and deep slow wave sleep
decreases.
– Most dreaming occurs during REM sleep.
– Non-REM dreams are described by subjects as “thinking” and
are less vivid and less hallucinatory.
Time Spent in Various Sleep Stages
Figure 15.6
Sleep and Dreaming
 Activation-Synthesis Hypothesis
 Dreams are a by-product that results when the brain uses
information from memory to make sense of random neural
activity generated by the brain stem.
 One hypothesis of REM sleep function is that it
promotes neural development during childhood.
 REM sleep makes up 50% of sleep during infancy and decreases
until adolescence, when it reaches adult levels
 Excitation that spreads through the brain from the pons during
REM sleep encourages differentiation, maturation, and
myelination in higher brain centers.
Sleep and Dreaming
 REM Sleep and Memory
 REM sleep increases following learning, and REM deprivation after
learning reduces retention.
 The amount of REM sleep corresponds to the quality of learning.
 Replay of activity that occurred during learning is synchronized
with theta activity in the hippocampus.
 After 4-7 days—the time required for memories to become
independent of the hippocampus—replay shifts out of phase with
theta.
 This may be a period of memory erasure. (Remember that out-ofphase stimulation produces long-term depression.)
 According to the reverse learning hypothesis, the brain achieves
efficiency by purging memories during REM sleep.
Sleep and Dreaming
• Non-REM Sleep and Memory
– Enhancing slow potentials (using TMS) improved
recall of word associations learned before sleep.
– According to Ribeiro, non-REM sleep is a period of
recall (replay) and REM sleep is a period of
consolidation.
– A 60-90 minute nap containing both REM and
non-REM sleep produces significant improvement
in learned performance.
– Overnight improvement on a learning task was
correlated with the percentage of slow-wave sleep
during the first quarter of the night and the
percentage of REM sleep during the final quarter.
Sleep and Dreaming
• Sleep Controls
– Adenosine accumulates during waking in the basal forebrain area
and inhibits arousal neurons there.
– Adenosine also stimulates sleep in the preoptic area.
• This area also responds to warming and probably accounts for
fever-induced sleepiness.
– Neurons in the ventrolateral preoptic area double their firing
during sleep.
• They inhibit neurons in arousal areas.
• Different parts induce REM and non-REM sleep.
 The pons sends impulses to the magnocellular nucleus of the
medulla to produce the atonia of REM sleep.
Brain Mechanisms of Sleep
Figure 15.9
Sleep and Dreaming
• The arousal system consists of two
major pathways.
– The PPT/LDT
• enables transmission through the thalamus to
the cortex
• and shifts the EEG to high-frequency, low
amplitude activity. (This pathway also is
active in the shift to REM sleep.)
◊
Sleep and Dreaming
– The second pathway activates the cortex to receive inputs from
the thalamus.
• The locus coeruleus and raphé nuclei are active during
waking, relatively quiet during non-REM, and almost silent
during REM.
• The tuberomamillary nucleus and the basal forebrain area
arouse the cortex.
• Neurons in the lateral hypothalamus send orexin-releasing
axons to several arousal centers.
• Orexin may stabilize the system by preventing inappropriate
switching into sleep.
Activity in the (a) locus coeruleus and (b) raphé nuclei from waking to post-REM.
Arousal Structures of Sleep and
Waking
Figure 15.10
Sleep and Dreaming
– REM sleep is characterized by PGO waves
• They travel from the pons through the lateral geniculate
nucleus of the thalamus to the occipital area.
• They apparently initiate the EEG desynchrony of REM sleep.
• They may account for the visual imagery of dreaming.
Sleep and Dreaming
• Insomnia is the inability to sleep or to obtain adequate
quality sleep, to the extent that the person feels
inadequately rested.
– Insomnia has also been linked to health conditions such as obesity and
decreased longevity.
– Insomnia is
• linked to stress;
• more common in people with affective disorders;
• often made worse by the use of sleeping pills;
• related to your chronotype, which indicates how your internal clock is
synchronized to the 24-hr day.
Chronotype and Sleep Disruption
Figure 15.14
(a) Ordinarily, a person falls
asleep when body
temperature (shown in red)
is decreasing and awakens
as it is rising.
(b) If body temperature is
phase delayed, the person
has trouble falling asleep.
(c) If body temperature is
phase advanced, the
person wakes up early.
Sleep and Dreaming
 Bedwetting, night terrors, and sleep walking occur during
slow wave sleep.
 Although sleepwalking is most frequent in childhood, about 3%
to 8% of adults sleepwalk.
 Sleepwalking is at least partially genetic, and can be triggered by
stress, alcohol, and sleep deprivation.
 Sleepwalking has even been used as a defense in crimes
committed, allegedly, during a sleepwalking episode.
 Sleep-related eating disorder is a condition in which people raid
the refrigerator while they are asleep, often consuming junk
food and gaining considerable weight.
◊
Sleep and Dreaming
 Narcolepsy is a disorder in which individuals fall
asleep suddenly during the daytime and go
directly into REM sleep.
 People with narcolepsy do not have clear boundaries between
sleep and waking, possibly due to abnormalities in the orexin
system.
 Narcoleptic dogs have a mutated orexin receptor gene .
• In humans, orexin-secreting neurons apparently are
destroyed by an autoimmune reaction, due to an HLA
immune system gene.
 Another symptom of narcolepsy is cataplexy, in which the
person falls to the floor paralyzed but fully awake.
Cataplexy in a Dog
Figure 15.15
Sleep and Dreaming
 REM sleep behavior disorder is almost the opposite of
cataplexy.
 People with this disorder lack the usual REM atonia and are
uncharacteristically physically active during REM sleep, often to the
point of injuring themselves or their bed partners.
 It is often associated with a neurological disorder, such as Parkinson’s
disease or a brain stem tumor.
 Lewy bodies in the medulla may affect the ability of the
magnocellular nucleus to produce the atonia of REM sleep.
◊
Sleep and Dreaming
• How conscious are we during sleep?
– According to Francis Crick, REM sleep is a state of diminished
consciousness and we are unconscious during non-REM sleep.
– Lucid dreamers are semi-conscious; they are aware they are
dreaming and can manipulate their dreams.
– Sleepwalkers engage in many activities during non-REM sleep that we
would expect to see only in the waking state, such as driving a car
and eating.
• One solution is to think of sleep as a different state of
consciousness along a continuum of consciousness.
The Neural Basis of Consciousness
• Consciousness
– refers to a state: a person is conscious or unconscious;
– indicates a sense of conscious experience, or awareness of
something.
• Consciousness varies in level, with coma and
deep anesthesia on one extreme, alert
wakefulness on the other, and sleep in between.
• There are also altered states of consciousness,
including hypnosis, trances, and meditative
states.
• Most researchers agree that consciousness
involves awareness, attention, and a sense of
self.
The Neural Basis of Consciousness
• Several brain areas are considered important in awareness.
– The prefrontal cortex—it is active when a subject becomes aware
of a relationship between stimuli.
– The hippocampus, due to its role in declarative learning.
– The parietal lobes—its ability to locate objects in space is
considered necessary for combining an object’s features into a
conscious whole.
• Example: A patient with parietal lobe damage often attributed
an object’s color or movement to another object.
The Neural Basis of Consciousness
– Researchers have concluded that binding an object’s
characteristics involves synchronization of neural activity.
• For example, while viewing a moving object activity
becomes synchronized between V1 and V5 (which
processes movement).
• Synchronization involves brain activity in the gamma
range (30 - 90 Hz).
– However, much of behavior occurs outside awareness.
• Use of proprioceptive cues to maintain posture.
• Blindsight detection of “unseen” objects.
• Learning without awareness.
The Neural Basis of Consciousness
• Attention involves focusing on some neural inputs to
the exclusion of others.
– The Cheshire cat effect demonstrates how powerful attention is.
– The four-fold increase in car accidents while drivers are using a mobile
phone demonstrates that attention allocates limited resources.
• There are two attention networks.
– The dorsal network allocates attention under goal-directed control.
– The ventral network responds to stimulus demands.
The Neural Basis of Consciousness
– The anterior cingulate cortex (ACC) may play an executive
role in allocating attention.
• About 1 out of every 5 ACC neurons increases or
decreases firing during attention-demanding tasks.
• The ACC is active when the subject must rapidly read
color names printed in a non-congruent color (“green”
printed in blue).
• The researchers believe the ACC modulates activity in
attentional pathways to focus attention on the word’s
meaning and suppress attention to its color.
◊
The Neural Basis of Consciousness
 An important aspect of consciousness is a sense of
self.
– The sense of self includes
• identity – what we refer to as “I”
• and a sense of agency, the attribution of an action or
effect to ourselves.
 Mirror recognition studies suggest that sense of self develops
around 15 months of age.
– A few other species share this sense of self.
• Chimps, orangutans, elephants, porpoises, and even
magpies can recognize themselves in a mirror.
• Monkeys do not even, after 17 years of exposure.
The Neural Basis of Consciousness
• What are the neural correlates of sense of self?
– Damage to frontal-temporal areas that impairs episodic memory can
produce a detachment from the self.
– People with damage to the ACC and the insula may treat their mirror
image as a companion, intruder, or stalker.
– The insula and inferior parietal cortex appear to distinguish between
self as agent and other as agent.
• When subjects perceived they were controlling movements on a
computer, activity increased in the insula; activity shifted to the
inferior parietal cortex when the experimenter controlled.
• Schizophrenics who believe their behavior is controlled by others
show heightened parietal lobe activity.
The Neural Basis of Consciousness
 Body image is an important aspect of the sense of
self; we identify our body with our self.
– Body image:
• is so strong that it persists in the face of amputation,
resulting in phantom limb in 80% of amputees.
• is so strong that an amputee whose phantom arm extended
to the side had to walk sideways through doors.
• appears to be inborn, because even children born with
missing limbs experience phantoms.
 Body image resides primarily in parietal areas; damage or
malfunction leads to illusions such as denial that a limb is paralyzed
and out-of-body experience.
The Neural Basis of Consciousness
• Long-term memory is essential to the
sense of self.
– People who have lost their past memories have an
impaired sense of self.
– Korsakoff’s patients often confabulate, replacing
missing memories. As Sacks said, one patient had to
“make himself (and his world) up every moment.”
– Memory of the past “is what makes us us”—McGaugh
– Short-term memory loss has less effect.
• HM, for example, had many years of memories as
a background for interpreting current experience.
◊
The Neural Basis of Consciousness
• Researchers believe that mirror neurons contribute to
development of one’s theory of mind, which involves a
distinction between self and others.
– Inability of the anterior cingulate cortex to regulate mirror neuron
activity may explain autistic individuals’ deficiencies in theory of
mind.
– Mirror neurons are important in assessing others’ intention.
• Mirror neurons distinguished between the apparent intent of a
model reaching for food to eat versus reaching to clean up.
The Neural Basis of Consciousness
• Severing the corpus callosum to control seizures
creates a unique disorder of self.
– The hemispheres often engage in independent or even conflicting
behavior.
• One man shook his wife with his left hand (controlled by the
more emotional right hemisphere) while his right hand tried
to restrain the left.
• When the right hand is performing a spatial task, the left
hand (controlled by the more spatially capable right
hemisphere) sometimes intercedes.
◊
The Neural Basis of Consciousness
• The left hemisphere can give an accurate explanation why the right
hand chose a picture of a chicken; but it says the left hand chose
the shovel “to clean out the chicken shed” (rather than to shovel
snow).
 According to Gazzaniga, the left hemisphere is the “brain interpreter” that
integrates all ongoing cognitive processes; the right hemisphere has a
more primitive form of consciousness.
 But researchers who consider the right hemisphere as “less conscious”
may be confusing consciousness with the ability to verbalize the content
of consciousness.
The Neural Basis of Consciousness
 Dissociative identity disorder involves shifts in
consciousness and behavior that appear to be distinct
personalities.
 Childhood physical and/or sexual abuse is reported in 90-95% of cases.
 The development of alternate personalities might be a way the child
escapes from persistent abuse.
 Alters can differ in handedness, response to medications, immune
reactions, and physiological measures such as heart rate.
 The hippocampus increases and decreases activity when switching,
consistent with Bowen’s view that state-dependent learning is involved.
The Neural Basis of Consciousness
• Most theories of consciousness assume that
consciousness involves a widely distributed
network.
– As subjects become conscious of a visuallypresented stimulus, activity spreads from
visual to prefrontal areas and then through
most of the brain.
– One hypothesis is that gamma oscillations generated by a feedback
loop between the thalamus and cortex binds sensory information into
awareness.
– In addition, activity in the default mode network varies with levels of
consciousness.
Awareness and Arousal in
Consciousness
Figure 15.27
• The various states of consciousness can be
described along two continua, awareness and
arousal.
The Neural Basis of Consciousness
 Brain damage produces various deficiencies in consciousness; these must
be understood and assessed to determine prognosis and potential for
communication.
 Coma: unarousable and unresponsive to stimulation
 Vegetative state: reflexive responses to stimulation and sleep cycling,
but no voluntary interaction
 Minimal consciousness: some voluntary responses but inability to
communicate reliably
 Locked-in syndrome: full consciousness, but mostly uncommunicative
because of paralysis (due to brain stem lesions)
 Vegetative patients have communicated with
researchers by producing distinctive patterns of brain
activity.
PET Scans of Various Levels of
Consciousness