Physiology of sleep and dreaming

1
Physiology of sleep and dreaming

• The sleep cycle
• Dreaming
• Why do we sleep?

2
The sleep cycle

• Electronic recording EEG, EOG, EMG
• EEG patterns divide sleep into four stages
• 1 a waves, 8 - 12 Hz, low amplitude, moderate
  frequency, similar to drowsy wakefulness
• 2 slower frequency, higher amplitude, plus
• K complexes
• Sleep spindles
• 3 d waves appear, 1-2 Hz, large amplitude
• 4 Dominated by d waves

3
REM sleep phenomena

• Stage 1 EEG Paradoxical sleep
• EOG (and corneal bulge) show frequent eye
  movements, as if scanning a visual field.
• EMG shows loss of muscle tonus due to downward
  inhibition of a motor neurons, although muscles
  moving hands and feet may twitch.
• Many brain structures function as if awake.

4
More REM phenomena

• SNS is partially activated Increases blood
  pressure, respiration, and heart rate.
• Genital erection or partial erection Postage
  stamp test.
• Narrative dreaming
• CBF is high to visual cortex, low to inferior
  frontal cortex (Madsen, 1991)
• Eye movements match dream events
• One EEG waveform is unique to REM and wakeful
  scanning

5
Dream research

• External stimuli may be incorporated into a
  dream.
• Dream events happen in real time.
• Everyone dreams recall depends on when in the
  sleep cycle you awaken.
• Genital response is independent of dream content.
• Sleep-walking and talking are non-REM.

6
Interpretation of dreams

• Manifest content is symbolic of latent desires
  (Freud)
• Activation-synthesis theory cf. incorporation of
  external events into dreams.
• Lucid dreams Have you had one?

7
Why do we sleep?

• Restoration, recuperation or repair
• Waking life disrupts homeostasis
• Protection with the circadian cycle
• Circadian synthesis

8
Who sleeps?

• Mammals and birds
• Opossums, sloths, bats 19-20 hours daily
• Cats, dogs, rodents 12-15 hours daily
• Ruminant herbivores 2-3 hours daily
• Reptiles, amphibians, fish, and insects have
  cycles of inactivity
• Note that sleep time does not correlate with
  waking activity levels, but does relate to waking
  vulnerability.

9
Two interesting variations on sleep

• Cetaceans
• Indus dolphin
• Bottlenose dolphin and porpoise
• Flocking birds

10
Circadian rhythms

• Zeitgebers and the SCN
• Free-running rhythms and the 25-hour period
• Sleep deprivation within a circadian cycle is
  followed by less sleep, not more
• Internal desynchronization free-running body
  temperature cycle and sleep-wake cycle may
  desynchronize.

11
Resynchronization

• Jet lag and shift work
• Phase shift Delay is better than advance
• Morning melatonin phase-delays
• Afternoon melatonin phase-advances
• Evening melatonin is ineffective
• Bright light exposure has the opposite effects
• Strengthen zeitgebers like light and activity
  early in the new waking period

12
Sleep deprivation

• Under total, voluntary sleep deprivation,
  sleepiness is cyclical
• Greatest sleepiness from 3-6 a.m.
• Waking sleepiness is countered by activity
• Sleepiness increases only up to four days
• Active, complex tasks are not impaired
• Easy, boring tasks are impaired
• Microsleep emerges

13
Compensation for sleep deprivation

• Subsequent slow-wave, non-REM sleep is increased
• Stage 3 and 4 sleep is almost completely restored
• Involuntary sleep deprivation is stressful
• Executive rats on a carousel apparatus died
• Post-mortem exams showed stress symptoms

14
REM deprivation

• REM pressure
• REM rebound
• REM escape
• Three theoretical effects
• Mental disorder
• Amotivational syndrome
• Memory processing deficits
• But tricyclic antidepressants block REM with none
  of these side effects.

15
Neural control of sleep

• Is sleep a passive process?
• The cerveau isole of Bremer (1936)
• The encephale isole and the RAS
• Partial transections leaving the RAS intact
• Ventrolateral Preoptic Area (VPA) triggers
  sleepiness and slow-wave sleep
• Warming the basal forebrain induces slow-wave
  sleep
• VPA receives input from thermoreceptors

16
More neural control

• PGO waves in the EEG from implanted electrodes
• Executive in the dorsolateral pons, called the
  peribrachial area.
• Kainic acid lesions of peribrachial area reduce
  REM sleep
• Carbachol, and ACh agonist, in ventral pons
  (medial pontine reticular formation) triggers REM
  phenomena.

17
EEG patterns
b
1 a
2 k
3 d
1 sec
18
EEG patterns...
4 d
1 sec