CHAPTER 9
WAKEFULNESS AND SLEEP
Chapter Outline
I.
Rhythms of Wakefulness and Sleep
A. Endogenous Cycles
1. Endogenous circannual rhythm: An internal calendar that prepares a species for annual seasonal
changes.
2. Endogenous circadian rhythm: Internal rhythms that last about a day (e.g., wakefulness and
sleepiness).
3. In humans, the circadian rhythm has a self-generated duration of about 24 hours.
4. Circadian rhythms are also present in eating, drinking, urination, secretion of hormone, sensitivity to
drugs, and other variables. Body temperature also fluctuates (36.7 degrees Celsius at night and 37.2
in the late afternoon).
5. Circadian rhythms also affect mood. On average, teenagers showed increase in positive mood from
waking until late afternoon, then a slight decline from then to bedtime. Most people report their most
pleasant mood around 5pm and their least pleasant mood around 5am.
6. One’s natural circadian rhythm predisposes them to be either “larks” (early risers) or “owls” (evening
people). This rhythm may change with age.
B. Setting and Resetting the Biological Clock
1. Zeitgeber: Stimulus that is necessary for resetting the circadian rhythm. Light is the dominant
zeitgeber for land animals.
2. Astronauts exposed to 45 minute intervals of light and dark are never fully alert during their wakeful
periods and they sleep poorly during their rest periods.
3. Most people are ill-rested and inefficient for days after the shift to daylight savings time.
4. Blind people sometimes use other zeitbegers (noise, temperature, meals, etc.) but those not sensitive
enough to secondary zeitbegers often experience insomnia at night and sleepiness during the day.
3. Jet Lag
a. Jet lag: A disruption of our biological rhythms due to crossing time zones.
b. Phase-delay: What happens to our circadian rhythms when we travel west, as we stay awake late
and awaken the next day already partly adjusted to the new schedule.
c. Phase-advance: What happens to our circadian rhythms when we travel east, as we tend to sleep
and awaken earlier than usual.
d. Recent studies have indicated that repeated adjustments of the circadian rhythm can increase
levels of cortisol, which can damage the hippocampus and cause memory loss.
4.
Shift Work
a. Night shift workers often have difficulty adjusting to their wake/sleep cycle (e.g., waking up
groggy, not sleeping well during the day, etc.). Working under lights comparable to noonday
may help shift the circadian rhythms.
b. Even after years of a night shift schedule, workers continue to feel groggy on the job and sleep
poorly during the day. Their body temperature continues to peak when they are sleeping in the
day instead of while they are working at night.
C. Mechanisms of the Biological Clock
1. The Suprachiasmatic Nucleus (SCN)
a.
2.
3.
2.
Nucleus located above the optic chiasm in the hypothalamus. The SCN controls the rhythms for
sleep and temperature. The neurons of the SCN generate impulses that follow a circadian
rhythm.
b. There is a genetic mutation in hamsters that causes the SCN to generate a 20-hour circadian
rhythm. When the SCN of these hamsters with a 20-hour rhythm was transplanted into adult
hamsters, the adults produced a 20-hour rhythm.
How Light Resets the SCN
a. The SCN is reset by the retinohypothalamic path that extends directly from the retina to the
SCN.
b. The retinal ganglion cells that reset the SCN are different from the ganglion cells that contribute
to vision and have their own photopigment called melanopsin that responds to slow changes in
overall duration of light.
c. These special ganglion cells are located near the nose, not evenly throughout the retina. This
way blind people have enough input to the melanopsin-containing ganglion cells to entrain their
waking and sleeping cycle to the local pattern of sunlight.
The Biochemistry of the Circadian Rhythm
a. In flies, the SCN regulates the circadian rhythms through the regulation of two genes, period
(per) and timeless (tim). The per and tim genes code for the proteins PER and TIM, respectively.
Early in the morning, the concentration of both PER and TIM are low and they increase during
the day. In the evening, protein concentrations are high and result in sleepiness. During the night,
the genes stop producing the proteins.
b. When PER and TIM levels are high, they feed back to inhibit the genes that produce the
messenger RNA molecules. When levels are low, the result is wakefulness.
c. Analyzing the mechanism in flies lead to research on humans. Mammals have three versions of
PER and several versions of TIM.
d. In humans, mutations in genes producing PER cause alterations in sleep schedules.
Melatonin
a. SCN regulates waking and sleeping by controlling the pineal gland which releases the hormone
melatonin, which increases sleepiness. Melatonin release usually starts 2 or 3 hours before
bedtime.
b. Melatonin stimulates receptors in the SCN to reset the biological clock.
II. Stages of Sleep and Brain Mechanisms
A. Sleep and Other Interruptions of Consciousness
1. Sleep: A state that the brain actively produces, characterized by decreased response to stimuli.
2. Coma: An extended period of unconsciousness caused by head trauma, stroke, or disease.
Characterized by low brain activity throughout the day and little or no response to stimuli, including
pain.
3. Vegetative State: A person alternates between periods of sleep and moderate arousal, although they
show no awareness of their surroundings.
4. Minimally Conscious State: A person shows occasional, brief periods of purposeful actions and
limited speech comprehension.
5. Brain Death: No sign of brain activity and no response to stimulation. In this case, physicians
generally wait 24 hours before pronouncing death.
B. Stages of Sleep
1. The electroencephalograph (EEG) records gross electrical potentials in an area of the brain through
electrodes attached to the scalp.
2. Polysomnograph: A combination of EEG and eye-movement records.
3.
Alpha waves have a frequency of about 8-12 brain waves per second; these waves are typical of a
relaxed state of consciousness.
4. Stage 1 sleep is a stage of light sleep noted by the presence of irregular, jagged, low-voltage waves.
5. Stage 2 sleep is characterized by sleep spindles (a burst of 12-14 Hz waves that last approximately
0.5 second) and K-complexes (sharp, high-amplitude waves followed by a smaller, positive wave).
6. Stages 3 and 4 are known as slow-wave sleep (SWS), which is comprised of slow, large-amplitude
waves.
C. Paradoxical or REM Sleep
1. Paradoxical sleep: Sleep stage discovered in cats in which the brain is very active but muscles are
completely relaxed. Named “paradoxical” because it is deep sleep in some ways and light in others.
2. Rapid eye movement (REM) sleep: Same as paradoxical sleep. Researchers discovered that
repeated eye movements were associated with paradoxical sleep. Also characterized by fast lowvoltage brain waves, plus breathing and heart rates similar to stage 1 sleep. Paradoxical sleep is
synonymous with REM sleep, except that many animal species lack eye movements.
3. Non-REM (NREM) sleep: The stages of sleep other than REM.
4. When people fall asleep, they enter stage 1, followed by stages 2, 3, and 4, in that order. Then they
cycle back from stage 4 through stages 3, 2, and then enter rapid eye movement (REM) sleep.
5. After entering REM sleep, the sleep cycle sequence repeats, with each complete cycle lasting 90
minutes.
6. Early in the night, stages 3 and 4 predominate, but toward morning, stage 4 grows shorter and REM
grows longer.
7. REM sleep is associated with dreaming, but dreams can happen in non-REM sleep.
D. Brain Mechanisms of Arousal and Attention
1. Brain Structures of Arousal and Attention
a. Reticular formation: A structure that extends from the medulla into the forebrain. Lesions
through the reticular formation decrease arousal.
b. Pontomesencephalon: A part of the reticular formation that contributes to cortical arousal.
Stimulation of the pontomesencephalon awakens a sleeping individual or increases alertness in
someone already awake.
c. : A structure in the pons that is inactive at most times but emits impulses, releasing
norepinephrine, in response to meaningful events. The locus coeruleus is also important for
storing information. The locus coeruleus is usually silent during sleep.
d. Certain areas of the hypothalamus stimulate arousal by releasing the neurotransmitter histamine,
which produces excitatory effects throughout the brain. Antihistamine drugs produce drowsiness
if they cross the blood-brain barrier.
e. Locus coeruleus A different group of axons from the hypothalamus (primarily the lateral
nucleus of the hypothalamus) release the peptide neurotransmitter orexin (also called
hypocretin). Orexin is necessary for staying awake.
f. Basal forebrain: An area just anterior and dorsal to the hypothalamus. Some of the axons from
the basal forebrain release GABA and are essential for sleep. These neurons receive input from
the anterior and preoptic areas of the hypothalamus. Another set of axons in the basal forebrain
release acetylcholine.
2. Sleep and the Inhibition of Brain Activity
a. During sleep, body temperature and metabolic rate decrease slightly.
b. Sleep depends on GABA-mediated inhibition. While spontaneously active neurons continue to
fire at a normal rate, we are unconscious because GABA inhibits synaptic activity.
c. Sleep can be localized. Sleepwalking is possible because a sleepwalker is awake in one part of
the brain and asleep in another part.
E. Brain Function in REM Sleep
1. During REM sleep, activity increases in the pons, the limbic system, and the parietal and temporal
cortex of the brain. Activity decreases in the primary visual cortex, the motor cortex, and the
dorsolateral prefrontal cortex.
2.
PGO (pons-geniculate-occipital ) waves: A distinctive pattern of high-amplitude electrical potentials
associated with REM sleep. The waves are detected first in the pons, shortly afterward in the lateral
geniculate nucleus of the thalamus, and then in the occipital cortex.
3.
REM sleep depends on both serotonin and acetylcholine activity for its onset and continuation.
Stimulation of acetylcholine synapses quickly moves a sleeper into REM, and serotonin interrupts or
shortens REM sleep. Norepinephrine from the locus coeruleus also blocks REM sleep.
F. Sleep Disorders
1. Insomnia: Inadequate sleep characterized by how one feels the following day.
2. Insomnia can result from a number of causes, including noise, uncomfortable temperatures, stress,
pain, diet, and medications. Certain psychiatric and neurological disorders (e.g., epilepsy, Parkinson’s
disease, brain tumors, depression, and anxiety) are also associated with insomnia.
3. Insomnia may be due to shifts in circadian rhythms (e.g., trying to sleep while body temperature
rises).
a. Phase delayed: shift in rhythm where someone has trouble falling asleep at the usual time.
b. Phase advanced: shift in rhythm where someone falls asleep easily but awakens early.
4. Paradoxically, the use of tranquilizers, such as sleeping pills, can lead to insomnia.
5. Sleep Apnea
a. Inability to breathe during sleep.
b. Symptoms include sleepiness during the day, impaired attention, depression, and sometime heart
problems.
c. People with sleep apnea have many brain areas that appear to have lost neurons. They
consequently show deficiencies of learning, reasoning, attention, and impulse control.
d. Research with mice suggests that sleep apnea leads to the aforementioned deficiencies (not the
other way around) because of the deprivation of oxygen.
e. Genetics, hormones, and obesity are all causes of this disorder.
6. Narcolepsy
a. A disorder characterized by frequent unexpected periods of sleepiness during the day.
b. Symptoms include gradual or sudden attacks of sleepiness, occasional cataplexy (attack of
muscle weakness while awake), sleep paralysis (inability to move while asleep), and hypnagogic
hallucination (dreamlike experiences occurring at the onset of sleep).
c. Each of the symptoms of narcolepsy is interpreted as REM sleep intruding into wakefulness.
d. People with narcolepsy lack the hypothalamic cells that produce and release orexin.
e. Narcolepsy is currently treated with stimulant drugs such as methylphenidate (Ritalin).
7. Periodic limb movement disorder: Repeated involuntary movements of the legs and arms that can
cause insomnia. The limb movements occur mostly during NREM sleep. This disorder is often
treated with tranquilizers.
8. REM behavior disorder: Disorder where people move around vigorously during their REM periods
apparently acting out their dreams. Likely due to the inability of the pons to inhibit spinal motor
neurons.
9. Night Terrors and Sleepwalking
a. Night terrors: An abrupt, anxious awakening from NREM sleep; this disorder is more common
in children than adults.
b. Sleepwalking: Usually occurs during stages 3 or 4 early in the night and is more common in
children than adults. Usually runs in families. It is more common when people are sleep
deprived or under unusual stress.
c. Sleep sex or “Sexsomnia”: an analogous condition in which sleeping people engage in sexual
behavior either with a partner or by masturbation.
III.
Why Sleep? Why REM? Why Dreams?
A. Functions of Sleep
1. Sleep and Energy Conservation
a.
b.
2.
3.
Sleep may have evolved to serve different purposes that it did in the distant past.
For most animals, sleep conserves energy during times when the animal is inefficient. Animals
also increase sleep during food shortages (i.e., hibernation).
c. Animal species vary in their sleep habits in accordance with how many hours per day they
devote to finding food, how safe they are from predators while they sleep, and other aspects of
their way of life.
d. Some species that are efficient at all hours of the day and night have evolved to never sleep (e.g.,
some fish species, dolphins after giving birth, some bird species).
Sleep and Memory
a. Another function of sleep is improved memory. Young adults deprived of a night’s sleep show
deficits on memory tasks. In contrast, if someone learns something and then goes to sleep, even
for a short time, memory after sleeping is improved.
b. Research shows that the patterns that occur in the brain during sleep resembled those that
occurred during learning, yet were more rapid during sleep. This suggests the brain replays its
daily experiences during sleep and reinforces the learning through repetition.
c. Sleep strengthen memory selectively by reinforcing certain synaptic connections and weakening
others to prevent over-activity of the brain.
d. During sleep, the brain also exhibits spindle activities of sleep spindles, which increase in
number after new learning.
Functions of REM Sleep
a. Species with the most total sleep also have the highest percentage of REM sleep. Human infants
spend more time in REM sleep and get more total sleep than adults. Adults who get the most
sleep have the most REM sleep and adults who get the least sleep get the least amount of REM.
b. Depriving people of sleep early in the night (non-REM sleep) leads to impairment of verbal
learning. Depriving people of sleep the latter half of the night (REM sleep deprivation) leads to
impaired consolidation of learned motor skills. REM deprivation also leads to increased
attempts at REM sleep.
c. REM sleep has been implicated as a useful tool for memory storage. It is a way of consolidating
different types of memories.
d. Research suggests that REM sleep may also be a way of getting oxygen to the corneas.
C. Biological Perspectives on Dreaming
1. Activation-Synthesis Hypothesis: During sleep, many brain regions become activated, so the brain
creates a story to make sense of all this activity.
4. Clinico-Anatomical Hypothesis: Either internal or external stimulation activates parts of the parietal,
occipital, and temporal cortex. No visual information overrides the stimulation and no criticism of the
prefrontal cortex censors it, so it develops into hallucinatory perceptions.