Biological Rhythms, Sleep, and Dreaming

1
Biological Rhythms,Sleep, and Dreaming
2
14 Biological Rhythms, Sleep, and Dreaming

• Biological Rhythms
• Many Animals Show Daily Rhythms in Activity
• The Hypothalamus Houses an Endogenous Circadian
  Clock
• Animals Use Circannual Rhythms to Anticipate
  Seasonal Changes

3
14 Biological Rhythms, Sleep, and Dreaming

• Sleeping and Waking
• Human Sleep Exhibits Different Stages
• The Sleep of Different Species Provides Clues
  about the Evolution of Sleep
• Our Sleep Patterns Change across the Life Span
• Manipulating Sleep Reveals an Underlying Structure

4
14 Biological Rhythms, Sleep, and Dreaming

• What are the Biological Functions of Sleep?
• At Least Four Interacting Neural Systems Underlie
  Sleep
• Sleep Disorders Can Be Serious, Even
  Life-Threatening

5
Many Animals Show Daily Rhythms in Activity

• Circadian rhythms are those functions of a living
  organism that display a rhythm of about 24 hours.
• Rhythms may be behavioral, physiological, or
  biochemical.
• Diurnalactive during the light
• Nocturnalactive during the dark

6
Figure 14.1 How Activity Rhythms are Measured
(Part 1)
7
Many Animals Show Daily Rhythms in Activity

• Circadian rhythms are generated by an endogenous
  (internal) clock.
• A free-running animal is maintaining its own
  cycle with no external cues, such as light.
• The period, or time between successive cycles,
  may not be exactly 24 hours.

8
Figure 14.1 How Activity Rhythms are Measured
(Part 2)
9
Many Animals Show Daily Rhythms in Activity

• A phase shift is the shift in activity in
  response to a synchronizing stimulus, such as
  light or food.
• Entrainment is the process of shifting the
  rhythm.
• The cue that an animal uses to synchronize with
  the environment is called a zeitgebertime-giver

10
The Hypothalamus Houses an Endogenous Circadian
Clock

• The biological clock is in the suprachiasmatic
  nucleus (SCN)located above the optic chiasm in
  the hypothalamus.
• Studies showed that circadian rhythms were
  disrupted in SCN-lesioned animals.
• Isolated SCNs can maintain electrical activity
  synchronized to the previous light cycle.

11
Figure 14.2 The Effects of Lesions in the SCN
12
Figure 14.3 The Circadian Rhythm of Metabolic
Activity of the SCN
13
The Hypothalamus Houses an Endogenous Circadian
Clock

• Transplant studies proved that the endogenous
  period is generated in the SCN.
• Hamsters with abolished circadian rhythms
  received an SCN tissue transplant from hamsters
  with a very short period, 20 hours.
• The rhythms were restored but matched the shorter
  period of the donor.

14
Figure 14.4 Brain Transplants Prove that the SCN
Contains a Clock
15
The Hypothalamus Houses an Endogenous Circadian
Clock

• Circadian rhythms entrain to lightdark cycles
  using different pathways, some outside of the
  eye.
• In amphibians and birds, the pineal gland is
  sensitive to light.
• In mammals, light information goes from the eye
  to the SCN via the retinohypothalamic pathway.

16
The Hypothalamus Houses an Endogenous Circadian
Clock

• The retinohypothalamic pathway consists of
  retinal ganglion cells that project to the SCN.
• These ganglion cells do not rely on rods and
  cones.
• Most of these retinal ganglion cells contain
  melanopsin, a special photopigment, that makes
  them sensitive to light.

17
Figure 14.5 The Retinohypothalamic Pathway in
Mammals
18
Figure 14.6 Schematic Showing the Components of
a Circadian System
19
The Hypothalamus Houses an Endogenous Circadian
Clock

• Molecular studies in Drosophila using mutations
  of the period gene helped to understand the
  circadian clock in mammals.
• SCN cells in mammals make two proteins
• Clock
• Cycle

20
The Hypothalamus Houses an Endogenous Circadian
Clock

• Clock and Cycle proteins bind together to form a
  dimer.
• The Clock/Cycle dimer promotes transcription of
  two genes
• Period (per)
• Cryptochrome (cry)

21
The Hypothalamus Houses an Endogenous Circadian
Clock

• Proteins arising from per and cry bind to each
  other and to a third one, Tau.
• The Per/Cry/Tau protein complex enters the
  nucleus and inhibits the transcription of per and
  cry.
• No new proteins are made, until the first set
  degrades and the cycle begins again every 24
  hours.

22

Figure 14.7 A Molecular Clock in Flies and Mice
23
The Hypothalamus Houses an Endogenous Circadian
Clock

• Light entrains the molecular clock in different
  ways.
• In flies, light reaches the brain directly and
  degrades a clock protein.
• In mammals, melanopsin cells detect light and
  release glutamate in the SCN.
• Glutamate triggers events that promote production
  of the Per protein, which in turn shifts the
  clock and the animals behavior.

24
The Hypothalamus Houses an Endogenous Circadian
Clock

• Gene mutations show how important the clock is to
  behavior in constant conditions
• tau mutationsthe period is shorter than normal
• Double Clock mutantsarrhythmic
• Single Clock mutantsperiod is longer than normal

25

Figure 14.8 When the Endogenous Clock Goes Kaput
26
The Hypothalamus Houses an Endogenous Circadian
Clock

• Some biological rhythms are shorter, such as
  bouts of activity, feeding, and hormone release.
• These ultradian rhythms occur more than once per
  day.
• Period length can be from minutes to hours.

27
Animals Use Circannual Rhythms to Anticipate
Seasonal Changes

• Other biological rhythms are long, such as body
  weight, and reproductive cycles.
• An endogenous circannual clock, separate from the
  SCN, runs at 365 days.
• Infradian rhythms occur less than once per day.

28
Figure 14.9 A Hamster for All Seasons
29
Sleeping and Waking

• Sleep is synchronized to external events,
  including light and dark.
• Stimuli like lights, food, jobs, and alarm clocks
  entrain us to be awake or to sleep.
• In the absence of cues, humans have a
  free-running period of 25 hours that varies with
  age.

30
Figure 14.10 Humans Free-Run Too
31

Figure 14.11 Oh, How I Hate to Get Out of Bed in
the Morning
32
Human Sleep Exhibits Different Stages

• Electrical brain potentials can be used to
  classify levels of arousal and states of sleep.
• Electroencephalography (EEG)records electrical
  activity in the brain
• Electro-oculography (EOG)records eye movements
• Electromyography (EMG)records muscle activity

33
Human Sleep Exhibits Different Stages

• Two distinct classes of sleep
• Slow-wave sleep (SWS)can be divided into four
  stages and is characterized by slow-wave EEG
  activity
• Rapid-eye-movement sleep (REM)characterized by
  small amplitude, fast-EEG waves, no postural
  tension, and rapid eye movements

34
Human Sleep Exhibits Different Stages

• The pattern of activity in an awake person
  contains many frequencies
• Dominated by waves of fast frequency and low
  amplitude (15 to 20 Hz).
• Known as beta activity or desynchronized EEG
• Alpha rhythmoccurs in relaxation, a regular
  oscillation of 8 to 12 Hz

35
Human Sleep Exhibits Different Stages

• Four stages of slow-wave sleep
• Stage 1 sleepshows events of irregular frequency
  and smaller amplitude, as well as vertex spikes,
  or sharp waves
• Heart rate slows, muscle tension reduces, eyes
  move about
• Lasts several minutes

36
Human Sleep Exhibits Different Stages

• Stage 2 sleep
• Defined by waves of 12 to 14 Hz that occur in
  bursts, called sleep spindles
• K complexes appearsharp negative EEG potentials

37
Human Sleep Exhibits Different Stages

• Stage 3 sleep
• Continued sleep spindles as in stage 2
• Defined by the appearance of large-amplitude,
  very slow waves called delta waves
• Delta waves occur about once per second

38
Human Sleep Exhibits Different Stages

• Stage 4 sleep
• Delta waves are present about half the time
• REM sleep follows
• Active EEG with small-amplitude, high-frequency
  waves, like an awake person
• Muscles are relaxedcalled paradoxical sleep

39
Figure 14.12 Electrophysiological Correlates of
Sleep and Waking
40
Human Sleep Exhibits Different Stages

• In a typical night of young adult sleep
• Sleep time ranges from 7-8 hours.
• 45-50 is stage 2 sleep, 20 is REM sleep.
• Cycles last 90-110 minutes, but cycles early in
  the night have more stage 3 and 4 SWS, and later
  cycles have more REM sleep.

41

Figure 14.13 A Typical Night of Sleep in a
Young Adult
42
Human Sleep Exhibits Different Stages

• Vivid dreams occur during REM sleep,
  characterized by
• Visual imagery
• Sense that the dreamer is there
• Nightmares are frightening dreams that awaken the
  sleeper from REM sleep.
• Night terrors are sudden arousals from stage 3 or
  4 SWS, marked by fear and autonomic activity.

43

Figure 14.14 Night Terror
44
The Sleep of Different Species Provides Clues
about the Evolution of Sleep

• REM sleep evolved in some vertebrates
• Nearly all mammals display both REM and SWS,
  except the echidnaa monotreme, or egg-laying
  mammalthat may not have REM sleep
• Birds also display both REM and SWS sleep

45
Figure 14.15 Amounts of Different Sleep States
in Various Mammals
46
The Sleep of Different Species Provides Clues
about the Evolution of Sleep

• Marine mammals do not show REM sleep, perhaps
  because relaxed muscles are incompatible with the
  need to come to the surface to breathe.
• In dolphins and birds, only one brain hemisphere
  enters SWS at a time the other remains awake.

47

Figure 14.16 Sleep in Marine Mammals
48
The Sleep of Different Species Provides Clues
about the Evolution of Sleep

• A sleep cycle is a period of SWS followed by one
  of REM sleep.
• Most vertebrates show
• A circadian distribution of activity
• A prolonged phase of inactivity
• Raised thresholds to external stimuli
• Characteristic posture

49
Our Sleep Patterns Change across the Life Span

• Mammals sleep more during infancy than in
  adulthood.
• Infant sleep is characterized by
• Shorter sleep cycles
• More REM sleep50, which may provide essential
  stimulation to the developing nervous system

50
Figure 14.17 The Trouble with Babies
51

Figure 14.18 Human Sleep Patterns Change with Age
52
Our Sleep Patterns Change across the Life Span

• As people age, total time asleep declines, and
  number of awakenings increases.
• The most dramatic decline is the loss of time
  spent in stages 3 and 4
• At age 60 only half as much time is spent as at
  age 20by age 90 stages 3 and 4 have disappeared.

53
Figure 14.19 The Typical Pattern of Sleep in an
Elderly Person
54
Manipulating Sleep Reveals an Underlying Structure

• Effects of sleep deprivationthe partial or total
  prevention of sleep
• Increased irritability
• Difficulty in concentrating
• Episodes of disorientation
• Effects can vary with age and other factors.

55
Figure 14.20 I Need Sleep!
56
Manipulating Sleep Reveals an Underlying Structure

• Total sleep deprivation compromises the immune
  system and leads to death.
• The disease fatal familial insomnia is
  inheritedin midlife people stop sleeping and die
  7-24 months after onset of the insomnia.

57
Manipulating Sleep Reveals an Underlying Structure

• Sleep recovery is the process of sleeping more
  than normally, after a period of deprivation.
• Night 1stage 4 sleep is increased, but stage 2
  is decreased
• Night 2most recovery of REM sleep, which is more
  intense than normal with more rapid eye movements

58

Figure 14.21 Sleep Recovery after 11 Days Awake
59
What Are the Biological Functions of Sleep?

• Four functions of sleep
• Energy conservation
• Predator avoidance
• Body restoration
• Memory consolidation

60
What Are the Biological Functions of Sleep?

• Energy is conserved during sleep muscular
  tension, heart rate, blood pressure, temperature
  and rate of respiration are reduced
• Small animals sleep more than large ones, in
  correlation with their high normal metabolic rate.

61

Figure 14.22 Sleep Helps Animals to Adapt an
Ecological Niche
62
What Are the Biological Functions of Sleep?

• Sleep helps animals avoid predatorsanimals sleep
  during the part of the day when they are most
  vulnerable.
• Sleep restores the body by replenishing metabolic
  requirements, such as proteins. Growth hormone is
  only released during SWS.

63
What Are the Biological Functions of Sleep?

• Explanations for memory consolidation and
  learning vary from passive to active
• Sleep during the interval between learning and
  recall may reduce interfering stimuli.
• Memory typically decays and sleep may slow this
  down.
• Or, sleep, especially REM, may actively
  contribute through processes that consolidate the
  learned material.

64

Figure 14.23 A Nonsleeper
65
At Least Four Interacting Neural Systems Underlie
Sleep

• Sleep is an active state mediated by
• A forebrain system, displays SWS
• A brainstem system, activates the forebrain
• A pontine system, triggers REM sleep
• A hypothalamic system, affects the other three

66
At Least Four Interacting Neural Systems Underlie
Sleep

• Transection experiments showed that different
  sleep systems originate in different parts of the
  brain.
• Encéphale isolé, or isolated brain, is made by an
  incision between the medulla and the spinal cord.
• Animals showed signs of sleep and wakefulness,
  proving that the networks reside in the brain.

67
At Least Four Interacting Neural Systems Underlie
Sleep

• Cerveau isolé, or isolated forebrain, is made by
  an incision in the midbrain.
• The electrical activity in the forebrain showed
  constant SWS, but not REMthus the forebrain
  alone can generate SWS.

68
Figure 14.24 Brain Transections Reveal Sleep
Mechanisms
69
At Least Four Interacting Neural Systems Underlie
Sleep

• The constant SWS activity in the forebrain is
  generated by the basal forebrain.
• Neurons in this region become active at sleep
  onset and release GABA.
• GABA suppresses activity in the nearby
  tuberomamillary nucleus.

70
At Least Four Interacting Neural Systems Underlie
Sleep

• Reduced activity in the tuberomamillary nucleus
  suppresses wakefulness.
• General anesthetics make GABAA receptors in the
  tuberomamillary nucleus more sensitive to GABA
  and induce a SWS state.

71
At Least Four Interacting Neural Systems Underlie
Sleep

• The reticular formation is able to activate the
  cortex.
• Electrical stimulation of this area will wake up
  sleeping animals while lesions of this area
  promote sleep.
• The forebrain and reticular formation seem to
  guide the brain between SWS and wakefulness.

72
At Least Four Interacting Neural Systems Underlie
Sleep

• An area of the pons, near the locus coeruleus, is
  responsible for REM sleep.
• Some neurons in this region are only active
  during REM sleep.
• They inhibit motoneurons to keep them from
  firing, disabling the motor system during REM
  sleep.

73

Figure 14.25 The Brainstem Reticular Formation
74

Figure 14.26 Sleep Stage Postures
75
At Least Four Interacting Neural Systems Underlie
Sleep

• The study of narcolepsy revealed the hypothalamic
  sleep center.
• Narcolepsy sufferers
• Have frequent sleep attacks and excessive daytime
  sleepiness
• Do not go through SWS before REM sleep
• May show cataplexya sudden loss of muscle tone,
  leading to collapse

76
At Least Four Interacting Neural Systems Underlie
Sleep

• Narcoleptic dogs have a mutant gene for a
  hypocretin receptor.
• Hypocretin normally prevents the transition from
  wakefulness directly into REM sleep.
• Interfering with hypocretin signaling leads to
  narcolepsy.

77
Figure 14.27 Narcolepsy in Dogs
78
At Least Four Interacting Neural Systems Underlie
Sleep

• Hypocretin neurons in the hypothalamus project to
  other brain centers the basal forebrain, the
  reticular formation and the locus coeruleus.
• Axons also go to the tuberomamillary nucleus,
  whose inhibition induces SWS.
• The hypothalamic hypocretin sleep center may act
  as a switch, controlling wakefulness, SWS sleep
  or REM sleep.

79
Figure 14.28 Neural Degeneration in Humans with
Narcolepsy
80
At Least Four Interacting Neural Systems Underlie
Sleep

• Sleep paralysis is the brief inability to move
  just before falling asleep, or just after waking
  up.
• It may be caused by the pontine center continuing
  to signal for muscle relaxation, even when awake.

81
Sleep Disorders Can Be Serious, Even
Life-Threatening

• Sleep disorders in children
• Night terrors and sleep enuresis (bed-wetting)
  are associated with SWS.
• Somnambulism (sleepwalking) occurs during stages
  3 and 4 SWS, and may persist into adulthood.

82
Sleep Disorders Can Be Serious, Even
Life-Threatening

• REM behavior disorder (RBD) is characterized by
  organized behavior from an asleep person.
• It usually begins after age 50 and may be
  followed by beginning symptoms of Parkinsons
  disease.
• This suggests damage in the brain motor systems.

83
Sleep Disorders Can Be Serious, Even
Life-Threatening

• Sleep state misperception occurs when people
  report insomnia even when they were asleep.
• Sleep-onset insomnia is a difficulty in falling
  asleep, and can be caused by situational factors,
  such as shift work or jet lag.
• Sleep-maintenance insomnia is a difficulty in
  staying asleep and may be caused by drugs or
  neurological factors.

84
Sleep Disorders Can Be Serious, Even
Life-Threatening

• In sleep apnea, breathing may stop or slow
  downblood oxygen drops rapidly.
• Muscles in the chest and diaphragm may relax too
  much or pacemaker respiratory neurons in the
  brain stem may not signal properly.
• Sleep apnea may be accompanied by snoring.

85
Sleep Disorders Can Be Serious, Even
Life-Threatening

• Each episode of sleep apnea arouses the person to
  restore breathing, but may result in daytime
  sleepiness.
• Treatments include a removable tube in the throat
  or a CPAP (continuous positive airway pressure)
  machine, to prevent collapse of the airways.

86
Figure 14.29 A Machine That Prevents Sleep Apnea
87
Sleep Disorders Can Be Serious, Even
Life-Threatening

• Untreated sleep apnea can lead to cardiovascular
  disorders.
• Sudden infant death syndrome (SIDS) is sleep
  apnea resulting from immature respiratory
  pacemaker systems or arousal mechanisms.
• Putting babies to sleep on their backs can
  prevent suffocation due to apnea.

88
Figure 14.30 Back to Sleep
89
Sleep Disorders Can Be Serious, Even
Life-Threatening

• Sleeping pills are not perfectmost bind to GABA
  receptors throughout the brain. Continued use of
  sleeping pills
• Makes them ineffective
• Produces marked changes in sleep patterns that
  persist even when not taking the drug
• Can lead to drowsiness and memory gaps