Circadian Rhythms, Sleep and Dreaming

1
Circadian Rhythms Sleep

• Circadian Rhythms (9.1)
• endogenous cycles
• role of the suprachiasmatic nucleus
• setting/resetting biological clocks
• Sleep (9.2)
• sleep stages
• REM sleep
• Functions of Sleep (9.3)
• why sleep?

2
Circadian Rhythms

• Endogenous circadian rhythms
• our bodies generate rhythms that last about a
  day
• humans last around 24.2 h
• Examples
• -activity
• -temperature
• -waking and sleeping
• -secretion of hormones
• -eating and drinking

Body temp. peaks 6h prior to sleep onset
Body temp. at lowest 2h after sleep onset
sleep onset
3
Suprachiasmatic Nucleus (SCN)

• located on the ventral surface of the brain
• site of our biological clock
• provides the main control of the circadian
  rhythms for sleep, temperature, and locomotor
  activity
• damage to the SCN disrupts behavior that is
  governed by circadian rhythms (e.g., sleep wake
  cycle)
• entrained by zeitgebers

4
What sets the Clock?
Zeitgeber a stimulus that resets the biological
clock (eg. bright light, exercise, temperature)
inactive
active
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What messes with the Clock?
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What Resets the Clock?

• Light
• retinal ganglion cells send direct projections
  to the SCN
• this provides information about light to the
  SCN
• light can also alter blood-borne factors
• SCN is highly vascularized
• Melatonin
• secreted from the pineal gland
• increased levels of melatonin make you sleepy
• melatonin can act on receptors in the SCN to
  phase-advance the
• biological clock

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Sleep
8
Sleep Stages
a-waves
slow waves
EEG
Eye movements
Time
irregular low voltage waves
slow waves
9
Sleep Stages
10
REM Sleep

• REM rapid-eye movement
• lots of brain activity - EEG shows low voltage
  fast waves
• postural muscles are most relaxed during REM
  sleep
• loose associative thinking
• PGO waves - start in the pons ? geniculate
  nucleus of thalamus ? occipital cortex

11
REM Sleep

• neurons within the pons send inhibitory messages
  to the spinal cord during REM sleep
• this message inhibits motor neurons that project
  to large muscles
• REM sleep is still observed after damage to the
  pons
• but, no inhibition of muscle neurons

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Function of REM Sleep

• Sleep deprivation studies suggest that REM sleep
  serves an important biological function
• subjects attempt to ? REM
• mild, temporary personality changes
• when uninterrupted, increased REM
• 1) Memory Storage
• animals ? REM after learning something
• 2) Getting Oxygen to
• the Corneas

13
Why Sleep?

• - conserve energy during inefficient or
  dangerous times (evolutionary theory)
• enables the body and brain to repair itself after
  working hard all day
• (repair and restoration theory)

14
Why Dream?

• Activation-Synthesis Hypothesis
• dreams begin with episodic bursts of spontaneous
  activity in the pons (PGO waves)
• these PGO waves partially activate certain
  regions of the cortex
• this haphazard cortical input is combined with
  previous (waking) input
• cortex synthesizes a story to make sense of
  all the input it is receiving

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Sleep Disorders

• Insomnia
• habitual sleeplessness
• possible causes excessive noise, stress,
  drugs, medications, pain, uncomfortable
  temperature, shift work
• three forms onset, maintenance, termination
• Narcolepsy
• frequent, unexpected periods of sleepiness
  during the day
• affects about 1 in 1000 people
• symptoms extreme daytime sleepiness,
  cataplexy, sleep paralysis, hypnagogic
  hallucinations
• involvement of orexin (also called hypocretin)

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Sleep Disorders

• Sleep Apnea
• inability to breath while sleeping
• stop breathing for up to a minute, then awake
  gasping for air
• side effects daytime sleepiness, attention
  problems, depression, cell death
• causes genetics, obesity, aging
• Night Terrors
• experience of intense anxiety from which a
  person awakens screaming in terror
• occur during nonREM sleep
• more common in children
• Sleep Talking and Walking
• occurs mostly in children
• runs in families
• expressed early in the night during stage 3 and
  4 sleep