Circadian Rhythms, Sleep and Dreaming

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Sapolsky 11 Stress and a Good Nights Sleep

• Circadian Rhythms
• endogenous cycles
• role of the suprachiasmatic nucleus
• setting/resetting biological clocks
• Sleep
• why sleep?
• stages of sleep
• Dreaming
• why dream?

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Circadian Rhythms

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

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Suprachiasmatic Nucleus (SCN)
SCN - main control center for sleep and
temperature circadian rhythms
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What sets the Clock?
Zeitgeber a stimulus that resets the biological
clock (eg. bright light, exercise, temperature)
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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
• 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
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Sleep Stages
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After 11 days of total sleep deprivation
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So, what goes on in the brain in SWS?

• Areas that ? arousal shut down.
• Primary sensory areas also shut down.
• Areas involved in memory consolidation and
  retrieval dont shut down, but are isolated from
  sensory input.

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So, what goes on in the brain in REM?

• INCREASE in sensory integration, motor, limbic,
  memory areas.
• Why dont we move, if motor areas are activated?
• One brain area sends inhibitory input to the
  spinal cord to prevent movement.
• Frontal cortex shuts down, disinhibiting limbic
  system.

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Reticular formation (red) wakes the brain.Locus
coeruleus (blue) inhibits muscles.Basal
forebrain (yellow) ? SWS.
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Why Sleep?

• Repair and Restoration Theory
• Sleep enables the body and brain to repair itself
  after working hard all day
• Brain is 3 of total body weight, but uses
  almost ¼ of the energy.
• Going without sleep causes people to be
  irritable, dizzy, and to have hallucinations and
  impaired concentration
• Sleep-deprived rats bodies work harder
• BUT, how much we sleep does not depend on how
  much we worked that day

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Why Sleep?

• Evolutionary Theory
• we evolved to sleep so that we would conserve
  energy when we were least efficient
• during sleep body temperature decreases
• predicts that species will sleep different
  amounts depending on how much they must look for
  food and watch for predators

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Why Dream?

• Facilitate problem solving
• Facilitate memory consolidation
• Lots of REM sleep predicts better consolidation
  of emotional
• information.
• Lots of SWS predicts better consolidation of
  motor tasks.
• Lots of SWSREM predicts better consolidation of
  perceptual
• information.
• Patterns of activation of hippocampal neurons
  are repeated

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Sleep deprivation as a stressor

• Hypothalamic corticotropin INHIBITING factor
  (CIF) ? SWS
• I hr before waking CRH, ACTH, and GCs rise and
  ? waking.
• If you dont get enough sleep decline in stress
  hormones doesnt occur.
• In fact, stress hormones increase.
• If sleep-deprived, frontal cortex and other areas
  work overtime
• a bunch of unshaven gibbering neurons counting
  on their toes, having to ask the rest of their
  cortical buddies to help out with this tough math
  problem.

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Sleep deprivation as a stressor

• Airline flight attendants 5 vs. 15 days between
  transcontinental flights.
• Attendants for airline with 5 day interval had
  smaller temporal lobes, impaired explicit memory,
  higher GCs.

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Stress as a disruptor of sleep

• CRH suppresses sleep
• throws ice water on those happily dozing
  neurons
• Direct effect on neurons
• Also via SNS
• Inhibits mostly SWS, which is needed more than
  more shallow stages.
• GCs impair memory consolidation.
• Random wakening ? higher CGs than predictable
  awakening
• a sleeping brain is still a working brain.

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Summary

• SCN is biological clock
• A Zeitgeber is a regular stimulus that entrains
  the circadian rhythm.
• 90-minute cycles of 4 stages of SWS (1 through 4
  and back) plus REM.
• Sleep deprivation ? increases in stages 3 4 and
  REM on subsequent nights.
• The reticular formation in brain stem ? waking.
• Locus coeruleus inhibits spinal motor neurons
• Basal forebrain ? SWS

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Summary

• Memory consolidation occurs during sleep
• Emotional memories during REM
• Motor memories during SWS
• Perceptual memories during both SWS REM
• Corticotropin INHIBITING factor (CIF) may ? SWS
• CRH decreases sleep
• Sleep deprivation ? increased GCs and INCREASES
  cortical activity (inefficient).