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  • 1. Chapter 9 Wakefulness and Sleep
  • 2. 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.
  • 3. Rhythms of Waking and Sleep
    • All animals produce endogenous circadian rhythms, internal mechanisms that operate on an approximately 24 hour cycle.
    • Animals generate endogenous 24 hour cycles of wakefulness and sleep.
      • Also regulates the frequency of eating and drinking, body temperature, secretion of hormones, urination, and sensitivity to drugs.
  • 4. Rhythms of Waking and Sleep
    • 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.
  • 5. Rhythms of Waking and Sleep
    • 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.
  • 6. Rhythms of Waking and Sleep
    • Free-running rhythm is a rhythm that occurs when no stimuli resets it.
    • A zeitgeber is a term used to describe any stimulus that resets the circadian rhythms.
    • Light is the primary one.
    • Exercise, noise, meals, and temperature are others zeitgebers.
  • 7. Rhythms of Waking and Sleep
    • 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.
  • 8.  
  • 9. Rhythms of Waking and Sleep
    • Circadian rhythms remain consistent despite lack of environmental cues indicating the time of day
    • Most people can adjust to 23- or 25- hour day but not to a 22- or 28- hour day.
    • People who engage in shift work often fail to adjust completely.
  • 10. Rhythms of Waking and Sleep
    • Mechanisms of the circadian rhythms include the following:
      • The Suprachiasmatic nucleus
      • Genes that produce certain proteins
      • Melatonin levels
  • 11. Rhythms of Waking and Sleep
    • 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.
  • 12.  
  • 13. Rhythms of Waking and Sleep
    • The SCN generates circadian rhythms in a genetically controlled, unlearned manner.
    • Single cell extracted from the SCN and raised in tissue culture continues to produce action potential in a rhythmic pattern.
    • Various cells communicate with each other to sharpen the circadian rhythm.
  • 14. Rhythms of Waking and Sleep
    • 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.
  • 15.  
  • 16. Rhythms of Waking and Sleep
    • 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.
  • 17.  
  • 18. Rhythms of Waking and Sleep
    • 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.
  • 19. Rhythms of Waking and Sleep
    • 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.
  • 20. Stages of Sleep And Brain Mechanisms
    • Sleep is a state that the brain actively produces.
    • 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
  • 21. Stages of Sleep And Brain Mechanisms
    • 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
  • 22. Stages of Sleep And Brain Mechanisms
    • 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
  • 23. 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
  • 24.  
  • 25. Stages of Sleep And Brain Mechanisms
    • 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.
  • 26. Stages of Sleep And Brain Mechanisms
    • 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-complex - a sharp high-amplitude negative wave followed by a smaller, slower positive wave.
  • 27. Stages of Sleep And Brain Mechanisms
    • 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.
  • 28. Stages of Sleep And Brain Mechanisms
    • Rapid eye movement sleep (REM) are periods characterized by rapid eye movements during sleep.
    • Also know as paradoxical sleep 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.
  • 29.  
  • 30. Stages of Sleep And Brain Mechanisms
    • 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.
  • 31. Stages of Sleep And Brain Mechanisms
    • 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.
  • 32.  
  • 33. Stages of Sleep And Brain Mechanisms
    • 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.
  • 34. Stages of Sleep And Brain Mechanisms
    • 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.
  • 35. Stages of Sleep And Brain Mechanisms
    • 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.
  • 36.  
  • 37. Structure Neurotransmitter(s) it releases Effects on Behavior Pontomesencephalon Acetylcholine, glutamate Increases cortical arousal Locus coeruleus Norepinephrine Increases information storage during wakefulness; suppresses REM sleep Basal forebrain Excitatory cells Acetylcholine Excites thalamus and cortex; increases learning, attention; shifts sleep from NREM to REM Inhibitory cells GABA Inhibits thalamus and cortex Hypothalamus (parts) Histamine Increases arousal (parts) Orexin Maintains wakefulness Dorsal raphe and pons Serotonin Interrupts REM sleep
  • 38. Stages of Sleep And Brain Mechanisms
    • 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.
  • 39. Stages of Sleep And Brain Mechanisms
    • The hypothalamus contains neurons that release “histamine” to produce widespread excitatory effects throughout the brain.
      • Anti-histamines produce sleepiness.
  • 40. Stages of Sleep And Brain Mechanisms
    • 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 basal forebrain to stimulate neurons responsible for wakefulness and arousal.
      • The basal forebrain is an area just anterior and dorsal to the hypothalamus
  • 41. Stages of Sleep And Brain Mechanisms
    • Functions of the inhibitory neurotransmitter GABA are also important:
      • Decreasing the temperature and metabolic rate
      • Decreasing stimulation of neurons.
  • 42. Stages of Sleep And Brain Mechanisms
    • During REM sleep:
      • Activity increases in the pons (triggers on set of REM sleep) and limbic system (emotional systems), parietal cortex and temporal cortex.
      • Activity in the pons triggers onset of REM sleep
      • Activity decreases in the primary visual cortex, the motor cortex, and the dorsolateral prefrontal cortex.
  • 43. Stages of Sleep And Brain Mechanisms
    • 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.
  • 44.  
  • 45. Stages of Sleep And Brain Mechanisms
    • 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 REM.
  • 46.  
  • 47. Stages of Sleep And Brain Mechanisms
    • Insomnia is a sleep disorder associated with 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.
  • 48.  
  • 49. Stages of Sleep And Brain Mechanisms
    • 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 may 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.
  • 50.  
  • 51. Stages of Sleep And Brain Mechanisms
    • 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.
  • 52. Stages of Sleep And Brain Mechanisms
    • (Insomnia cont’d)
    • 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.
  • 53. Stages of Sleep And Brain Mechanisms
    • 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.
  • 54. Stages of Sleep And Brain Mechanisms
    • 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).
  • 55. Stages of Sleep And Brain Mechanisms
    • 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.
  • 56. Why Sleep? Why REM? Why Dreams?
    • Functions of sleep include:
      • Energy conservation.
      • Restoration of the brain and body.
      • Memory consolidation.
  • 57. Why Sleep? Why REM? Why Dreams?
    • The original function of sleep was to probably conserve energy.
    • Conservation of energy is accomplished via:
      • Decrease in body temperature of about 1-2 Celsius degrees in mammals.
      • Decrease in muscle activity.
  • 58. Why Sleep? Why REM? Why Dreams?
    • Animals also increase their sleep time during food shortages.
      • sleep is analogous to the hibernation of animals.
    • Animals sleep habits and 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.
  • 59.  
  • 60. Why Sleep? Why REM? Why Dreams?
    • Sleep enables restorative processes:
      • Proteins rebuilt in the brain
      • Energy supplies replenished
    • Moderate sleep deprivation results in impaired concentration, irritability, hallucinations, tremors, unpleasant mood, and decreased immune system functioning.
    • Caffeine increases arousal by blocking the receptors for adenosine (accumulate during wakefulness and increase drowsiness)
  • 61. Why Sleep? Why REM? Why Dreams?
    • 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.
  • 62. Why Sleep? Why REM? Why Dreams?
    • 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.
  • 63. Why Sleep? Why REM? Why Dreams?
    • 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.
  • 64.  
  • 65. Why Sleep? Why REM? Why Dreams?
    • 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.
  • 66. Why Sleep? Why REM? Why Dreams?
    • 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.
  • 67. Why Sleep? Why REM? Why Dreams?
    • 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.
  • 68. 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.
  • 69. Why Sleep? Why REM? Why Dreams?
    • 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.
  • 70. Why Sleep? Why REM? Why Dreams?
    • 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.
  • 71. Why Sleep? Why REM? Why 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.