Chapter 9 Wakefulness and Sleep • Rhythms of Waking and Sleep

• Chapter 9

Wakefulness and Sleep

• Rhythms of Waking and Sleep

• Some animals generate endogenous circannual rhythms, internal mechanisms that operate on an annual or yearly cycle.

– Example: Birds migratory patterns, animals storing food for the winter.


• 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.


Circadian rhythm:

• Remains consistent despite lack of environmental cues indicating the time of day

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

• Changes as a function of age.

– Example: sleep patterns from childhood to late adulthood.


• The purpose of the circadian rhythm is to keep our internal workings in phase with the outside world.

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

• Resetting our circadian rhythms is sometimes necessary.

• 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.


• Jet lag refers to the disruption of the circadian rhythms due to crossing time zones.

– Stems from a mismatch of the internal circadian clock and external time.

• Characterized by sleepiness during the day, sleeplessness at night, and impaired concentration.

• Traveling west “phase-delays” our circadian rhythms.

• Traveling east “phase-advances” our circadian rhythms.


• Mechanisms of the circadian rhythms include the following:

– The Suprachiasmatic nucleus.

– Genes that produce certain proteins.

– Melatonin levels.


• The suprachiasmatic nucleus (SCN) is part of the hypothalamus and the main control center of the circadian rhythms of sleep and temperature.

– Located above the optic chiasm.

– Damage to the SCN results in less consistent body rhythms that are no longer synchronized to environmental patterns of light and dark.


• Light resets the SCN via a small branch of the optic nerve known as the retinohypothalamic path.

– Travels directly from the retina to the SCN.

• The retinohypothalamic path comes from a special population of ganglion cells that have their own photopigment called melanopsin.

– The cells respond directly to light and do not require any input from the rods or cones.


• Two types of genes are responsible for generating the circadian rhythm.

– Period - produce proteins called Per.

– Timeless - produce proteins called Tim.

• Per and Tim proteins increase the activity of certain kinds of neurons in the SCN that regulate sleep and waking.

• Mutations in the Per gene result in odd circadian rhythms.


• 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.

• Stages of Sleep And Brain Mechanisms

• Sleep is a state that the brain actively produces – it is not a state of neural quiescence.

• Characterized by a moderate decrease in brain activity and decreased response to stimuli.

• Sleep differs from the following states:

– Coma

– Vegetative state

– Minimally conscious state

– Brain death


• Coma – extended period of unconsciousness caused by head trauma, stroke, or disease characterized by low brain activity that remains fairly steady

– Person shows little response to stimuli

• Vegetative state – person alternates between periods of sleep and moderate arousal but no awareness of surrounding

– Some autonomic arousal to painful stimulus

– No purposeful activity/ response to speech

• Minimally conscious state - one stage higher than a vegetative state marked by occasional brief periods of purposeful action and limited speech comprehension

• Brain death - no sign of brain activity and no response to any stimulus

– Stages of Sleep And Brain Mechanisms

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

• Allows researchers to compare brain activity at different times during sleep.

• A polysomnograph is a combination of EEG and eye-movement records (EOG).


• Sleep is a specialized state that serves a variety of important functions including:

– conservation of energy.

– repair and restoration.

– learning and memory consolidation.


• 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 REM.


• Alpha waves are present when one begins a state of relaxation.

• Stage 1 sleep is when sleep has just begun.

– the EEG is dominated by irregular, jagged, low voltage waves.

– brain activity begins to decline.


• Stage 2 sleep is characterized by the presence of:

– Sleep spindles - 12- to 14-Hz waves during a burst that lasts at least half a second.

– K-complexes - a sharp high-amplitude negative wave followed by a smaller, slower positive wave.


• Stage 3 and stage 4 together constitute slow wave sleep (SWS) and is characterized by:

– EEG recording of slow, large amplitude wave.

– Slowing of heart rate, breathing rate, and brain activity.

– Highly synchronized neuronal activity.


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

• Also known as “paradoxical sleep” because it is deep sleep in some ways, but light sleep in other ways.

• EEG waves are irregular, low-voltage and fast.

• Postural muscles of the body are more relaxed than other stages.


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

• When one falls asleep, they progress through stages 1, 2, 3, and 4 in sequential order.

• After about an hour, the person begins to cycle back through the stages from stage 4 to stages 3 and 2 and than REM.

• The sequence repeats with each cycle lasting approximately 90 minutes.


• Stage 3 and 4 sleep predominate early in the night.

– The length of stages 3 and 4 decrease as the night progresses.

• REM sleep is predominant later in the night.

– Length of the REM stages increases as the night progresses.

• REM is strongly associated with dreaming, but people also report dreaming in other stages of sleep.


• 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.

– Anti-histamines 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.


• Decreased arousal required for sleep is accomplished via the following ways:

– Decreasing the temperature of the brain and the body.

– Decreasing stimulation by finding a quiet environment.

– Accumulation of adenosine in the brain to inhibit the basal forebrain cells responsible for arousal.

– Caffeine blocks adenosine receptors.

4.

Accumulation of prostaglandins that accumulate in the body throughout the day to induce sleep.

– Prostaglandins stimulate clusters of neurons that inhibit the hypothalamic cells responsible for increased arousal.


• During REM sleep:

– Activity increases in the pons (triggers the onset of REM sleep), limbic system, parietal cortex and temporal cortex.

– Activity decreases in the primary visual cortex, the motor cortex, and the dorsolateral prefrontal cortex.


• REM sleep is also associated with a distinctive pattern of high-amplitude electrical potentials known as PGO waves.

• Waves of neural activity are detected first in the pons and then in the lateral geniculate of the hypothalamus, and then the occipital cortex.

• REM deprivation results in high density of PGO waves when allowed to sleep normally.


• 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.

• REM is also regulated by serotonin and acetylcholine.

– Drugs that stimulate Ach receptors quickly move people to REM.

– Serotonin interrupts or shortens REM.


• 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.

• Cognitive impairment can result from loss of neurons due to insufficient oxygen levels.

• 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.

• Seems to run in families although no gene has been identified.

• Caused by lack of hypothalamic cells that produce and release orexin.

• Primary treatment is with stimulant drugs which increase wakefulness by enhancing dopamine and norepinephrine activity.

– Stages of Sleep And Brain Mechanisms

• Periodic limb movement disorder (restless legs) 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.


• REM behavior disorder is associated with vigorous movement during REM sleep.

– Usually associated with acting out dreams.

– Occurs mostly in the elderly and in older men with brain diseases such as Parkinson’s.

– Associated with damage to the pons (inhibit the spinal neurons that control large muscle movements).


• “Night terrors” are experiences of intense anxiety from which a person awakens screaming in terror.

– Usually occurs in NREM sleep.

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

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

• Why Sleep? Why REM? Why Dreams?

• Functions of sleep include:

– Energy conservation.

– Restoration of the brain and body.

– Memory consolidation.


• The original function of sleep was to probably conserve energy – recuperative theory of sleep.

• Conservation of energy is accomplished via:

– Decrease in body temperature of about 1-2 Celsius degrees in mammals.

– Decrease in muscle activity.


• Animals also increase their sleep time during food shortages.

– sleep is analogous to the hibernation of animals.

• Animals sleep habits are influenced by particular aspects of their life including:

– how many hours they spend each day devoted to looking for food.

– Safety from predators while they sleep

• Examples: Sleep patterns of dolphins, migratory birds, and swifts.


• Sleep enables restorative processes in the brain to occur.

– Proteins are rebuilt.

– Energy supplies are replenished.

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


• People vary in their need for sleep.

– Most sleep about 8 hours.

• Prolonged sleep deprivation in laboratory animals results in:

– Increased metabolic rate, appetite and body temperature.

– Immune system failure and decrease in brain activity.


• Sleep also plays an important role in enhancing learning and strengthening memory.

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

• Increased brain activity occurs in the area of the brain activated by a newly learned task while one is asleep.

– Activity also correlates with improvement in activity seen the following day.


• Humans spend one-third of their life asleep.

• One-fifth of sleep time is spent in REM.

• Species vary in amount of sleep time spent in REM.

– Percentage of REM sleep is positively correlated with the total amount of sleep in most animals.

• Among humans, those who get the most sleep have the highest percentage of REM.


• REM deprivation results in the following:

– Increased attempts of the brain/ body for REM sleep throughout the night.

– Increased time spent in REM when no longer REM deprived.

• Subjects deprived of REM for 4 to 7 nights increased REM by 50% when no longer REM deprived.


• Research is inconclusive regarding the exact functions of REM.

• During REM:

– The brain may discard useless connections

– Learned motor skills may be consolidated.

• Maurice (1998) suggests the function of REM is simply to shake the eyeballs back and forth to provide sufficient oxygen to the corneas.


• 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:

– The activation-synthesis hypothesis.

– 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.

• Input from the pons activates the amygdala giving the dream an emotional content.

• Because much of the prefrontal cortex is inactive during PGO waves, memory of dreams is weak.

– Also explains sudden scene changes that occur in dreams.

– Why Sleep? Why REM? Why Dreams?

• 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.

– Stimulation is combined with recent memories and any information the brain is receiving from the senses.

• Since the brain is getting little information from the sense organs, images are generated without constraints or interference.

• Arousal can not lead to action as the primary motor cortex and the motor neurons of the spinal cord are suppressed.

• Activity in the prefrontal cortex is suppressed which impairs working memory during dreaming.

– Why Sleep? Why REM? Why Dreams?

Clinico-anatomical hypothesis (cont)

• Activity is high in the inferior part of the parietal cortex, an area important for visual-spatial perception.

– Patients with damage report problems with binding body sensations with vision and have no dreams.

– Activity is also high in areas outside of V1, accounting for the visual imagery of dreams.

• Activity is high in the hypothalamus and amygdala which accounts for the emotional and motivational content of dreams.

• Either internal or external stimulation activates parts of the parietal, occipital, and temporal cortex.

• Lack of sensory input from V1 and no criticism from the prefrontal cortex creates the hallucinatory perceptions.

Chapter 9 Wakefulness and Sleep • Rhythms of Waking and Sleep

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