psy3 chapter9 modified

Chapter 9Wakefulness and Sleep

Why Sleep? Why REM? Why Dreams?

• People vary in their need for sleep.– Most sleep about 8 (7 to 9) hours.

• Sleep is a specialized state that serves a variety of restorative processes including: ++++– Proteins are rebuilt.– Energy supplies are replenished.– Repair and restoration.– Learning and memory consolidation.

• Sleep deprivation results in impaired concentration, irritability, hallucinations, tremors, unpleasant mood, and decreased responses of the immune system.


• Sleep also plays an important role in enhancing learning and strengthening memory.– Increased brain activity occurs in the area

of the brain activated by a newly learned task while one is asleep. ++++

– Performance on a newly learned task is often better the next day if adequate sleep is achieved during the night.

Rhythms of Waking and Sleep

• All animals produce endogenous circadian rhythms, internal mechanisms that operate on an approximately 24 hour cycle.– Regulates the sleep/ wake cycle.– Also regulates the frequency of eating and

drinking, body temperature, secretion of hormones, volume of urination, and sensitivity to drugs.

• Can differ between people and lead to different patterns of wakefulness and alertness.

• Change as a function of age.– Example: sleep patterns from childhood to late

adulthood.


• Human circadian clock generates a rhythm slightly longer than 24 hours when it has no external cue to set it.

• Most people can adjust to 23- or 25- hour day but not to a 22- or 28- hour day.

• Bright light late in the day can lengthen the circadian rhythm.


• Mechanisms of the circadian rhythms include the following:– The Suprachiasmatic nucleus.– Genes that produce certain proteins.– Melatonin levels.


• The suprachiasmatic (supra-keye-asmatic) nucleus (SCN) is part of the hypothalamus and the main control center of the circadian rhythms of sleep and temperature. ++++– Damage to the SCN results in less

consistent body rhythms that are no longer synchronized to environmental patterns of light and dark.


• The SCN regulates waking and sleeping by controlling activity levels in other areas of the brain.– The SCN regulates the pineal gland, an

endocrine gland located posterior to the thalamus.

– The pineal gland secretes melatonin, a hormone that increases sleepiness. ++++


• Melatonin secretion usually begins 2 to 3 hours before bedtime.

• Melatonin feeds back to reset the biological clock through its effects on receptors in the SCN.

• Melatonin taken in the afternoon can phase-advance the internal clock and can be used as a sleep aid.– A zeitgeber (z-eye-t gee-ber) is a term used to

describe any stimulus that resets the circadian rhythms. ++++• Exercise, noise, meals, and temperature

are others zeitgebers.

Stages of Sleep And Brain Mechanisms

• The electroencephalograph (EEG) allowed researchers to discover that there are various stages of sleep.

• Over the course of about 90 minutes:– a sleeper goes through sleep stages 1, 2, 3, and 4– then returns through the stages 3 and 2 to a stage

called Rapid eye movement sleep (REM).• REM are periods characterized by rapid eye

movements during sleep where postural muscles of the body are more relaxed than other stages.

– Stages other than REM are referred to as non-REM sleep (NREM).

Fig. 7.6 (a) Average proportion of time adults spend daily in REM sleep and NREM sleep. REM periods add up to about 20 percent of total sleep time. (b) Typical changes in stages of sleep during the night. Notice that dreams mostly coincide with REM periods.


• Various brain mechanisms are associated with wakefulness and arousal.– The reticular formation is a part of the

midbrain that extends from the medulla to the forebrain and is responsible for arousal. ++++


• The pontomesencephalon is a part of the midbrain that contributes to cortical arousal.– Axons extend to the thalamus and basal

forebrain which release acetylcholine and glutamate

– produce excitatory effects to widespread areas of the cortex.

• Stimulation of the pontomesencephalon awakens sleeping individuals and increases alertness in those already awake. ++++


• The locus coeruleus is small structure in the pons whose axons release norepinephrine to arouse various areas of the cortex and increase wakefulness. ++++– Usually dormant while asleep.


• The basal forebrain is an area anterior and dorsal to the hypothalamus containing cells that extend throughout the thalamus and cerebral cortex.– Cells of the basal forebrain release the

inhibitory neurotransmitter GABA. ++++• Inhibition provided by GABA is essential

for sleep.– Other axons from the basal forebrain

release acetylcholine which is excitatory and increases arousal.


• The hypothalamus contains neurons that release “histamine” to produce widespread excitatory effects throughout the brain.– This explains why anti-histamines could

produce sleepiness.

• Orexin is a peptide neurotransmitter released in a pathway from the lateral nucleus of the hypothalamus highly responsible for the ability to stay awake. ++++– Stimulates acetylcholine-releasing cells in the

forebrain and brain stem to increase wakefulness and arousal.


• Cells in the pons send messages to the spinal cord which inhibit motor neurons that control the body’s large muscles. ++++– Prevents motor movement during REM

sleep.• Cells in the pons are also the origin of a

distinctive pattern of high-amplitude electrical potentials known as PGO waves (pons-geniculate-occipital).– REM sleep is associated with a high

density of PGO waves.


• Insomnia is a sleep disorder associated with inability to fall asleep or stay asleep.– Results in inadequate sleep.– Caused by a number of factors including noise,

stress, pain medication.– Can also be the result of disorders such as

epilepsy, Parkinson’s disease, depression, anxiety or other psychiatric conditions.

– Dependence on sleeping pills and shifts in the circadian rhythms can also result in insomnia.


• Sleep apnea is a sleep disorder characterized by the inability to breathe while sleeping for a prolonged period of time.– Consequences include sleepiness during the day,

impaired attention, depression, and sometimes heart problems.

– Causes include, genetics, hormones, old age, and deterioration of the brain mechanisms that control breathing and obesity.


• Narcolepsy is a sleep disorder characterized by frequent periods of sleepiness.

• Four main symptoms include:– Gradual or sudden attack of sleepiness.– Occasional cataplexy - muscle weakness triggered

by strong emotions.– Sleep paralysis- inability to move while asleep or

waking up.– Hypnagogic hallucinations- dreamlike experiences

the person has difficulty distinguishing from reality.


• Periodic limb movement disorder is the repeated involuntary movement of the legs and arms while sleeping.– Legs kick once every 20 to 30 seconds for periods

of minutes to hours.– Usually occurs during NREM sleep.


• “Night terrors” are experiences of intense anxiety from which a person awakens screaming in terror.– Usually occurs in NREM sleep.

• “Sleep talking” occurs during both REM and NREM sleep.

• “Sleepwalking” runs in families, mostly occurs in young children, and occurs mostly in stage 3 or 4 sleep.

Fig. 9-18, p. 289

THIS CHART IS ONLY ACCURATE IF YOU ARE VERY UNHEALTHY OR TAKING PRESCRIPTION MEDICATIONS AND IT DOES NOT REFLECT A POSSIBLE ADOLESCENT INCREASE IN SLEEP TIME


• Biological research on dreaming is complicated by the fact that subjects can not often accurately remember what was dreamt.

• Two biological theories of dreaming include:

1. The activation-synthesis hypothesis.

2. The clinico-anatomical hypothesis.


• The activation-synthesis hypothesis suggests dreams begin with spontaneous activity in the pons which activates many parts of the cortex. ++++– The cortex synthesizes a story from the

pattern of activation.– Normal sensory information cannot

compete with the self-generated stimulation and hallucinations result.


• The clinico-anatomical hypothesis places less emphasis on the pons, PGO waves, or even REM sleep. ++++– Suggests that dreams are similar to

thinking, just under unusual circumstances.• Similar to the activation synthesis hypothesis

in that dreams begin with arousing stimuli that are generated within the brain.– Brain stimulation is combined with recent

memories and any information the brain is receiving from the senses. ++++

psy3 chapter9 modified

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