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Week 10: Sleep & Biological
Rhythms
Psychology 372
Physiological Psychology
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Psyc 372 – Physiological Psychology
Week 10 Topics
• Lecture 1:
• Biological Rhythms
• Stages of Sleep
• Disorders of Sleep
• Lecture 2:
• Functions of sleep
• Mechanisms Underlying Sleep
• Dreaming
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Psyc 372 – Physiological Psychology
Why do we sleep?
• Recovery from sleep deprivation
• More time spent in Stage 4 and REM
• Less time spent in Stages 1 and 2
• Rats die in 2-3 weeks if sleep deprived, 4-6 weeks if
REM deprived
• Deep, Stage 3-4, slow-wave (delta) sleep may be needed
for recovery from oxidative stress
• High metabolism during awake activity produces
overabundance of free radicals: chemicals with
unpaired electrons that are therefore highly reactive
• Activity is brain-specific BRAIN RUST!
• High mental activity increases slow-wave sleep
• High physical activity is uncorrelated with slow3
wave and REM
Psyc 372 – Physiological Psychology
Why REM sleep?
• Necessary for brain development/learning?
• Greatest amount of REM occurs during early
development
• 70% of newborn sleep time
• 30% by 6 months
• 22% by 8 years
• 15% by late adulthood
• REM deprivation impedes maze learning in
rats
• Percentage of REM time is positively
correlated with maze-learning performance
and during exam time
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Psyc 372 – Physiological Psychology
Other Functions of Sleep
• Thermoregulation
• Heating of hypothalamus induces sleep
• Body heating leads to more slow-wave
sleep in humans
• Sleep-deprived rats
• prefer higher ambient temperatures (10
degrees Celsius or more!)
• Show drop in body core temperature
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Psyc 372 – Physiological Psychology
What is Dreaming?
• Predominantly reported when awoken from REM
• Dream duration positively correlated with REM duration
• Dream mood, anxiety, imaginativeness, expressiveness
positively correlated with waking state the daily residue
• Hobson and McCarley (1977) Activation-synthesis
• Forebrain interprets ambiguous brain activity during REM
• Nightmares
• Fear-based dreams during REM
• Occur frequently (1+/week) in 2-10% of population
• More often reported by women
• Genetic component governs frequency
• Occur more often during periods of intense stress
• Is there a function of dreaming or is it simply an
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epiphenomenon of REM?
Psyc 372 – Physiological Psychology
Mechanisms of Arousal
• Alertness/arousal governed
by 5 neurotransmitters
• Acetylcholine
• pons and basal forebrain
• produces cortical arousal
• Norepinephrine
• locus coeruleus (LC) in dorsal
pons
• increases arousal and
vigilance, also related to
stress
• Serotonin
• raphe nuclei of reticular
formation
• increases cortical arousal,
facilitates continuous,
automatic movements
• Histamine
• Tuberomammillary nucleus
(TMN) of the hypothalamus
• Increase cortical arousal
directly and indirectly
through release of
acetylcholine
• Hypocretin
• Lateral hypothalamus
• Stimulate LC, raphe nuclei,
TMN, doral pons forebrain,
cerebral cortex
• Facilitates motor activity and
muscle tone
• Counteracts
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“laughter weakness”?
Psyc 372 – Physiological Psychology
Mechanisms Regulating Slow-wave Sleep
• Activity in ventrolateral preoptic area (VLPA) and
median preoptic nucleus (MnPN) neurons increases
during sleep
• Project inhibitory axons (secreting GABA) to TMN, dorsal
pons, raphe nuclei, and LC, which govern arousal
• Receives inhibitory input from TMN, raphe nuclei, and LC
• Mutual inhibition forms flip-flop circuit that controls sleep
vs. wakefullness
• Adenosine decreases release of GABA in VLPA
• increases delta-wave (slow-wave, deep sleep) activity
• Astrocytes store glycogen as a back-up nutrient for
when glucose levels are inadequate do to overactivity
• Metabolism of glycogen produces accumulation of
adenosineleads to symptoms of sleep deprivation
• During delta activity glycogen gets restored
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• Caffeine blocks adenosine receptors
Psyc 372 – Physiological Psychology
The Deep Sleep Switch
Adenosine sensitive
neurons in basal
forebrain that inhibit
VLPA
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Psyc 372 – Physiological Psychology
Control of REM Sleep
• PGO (pons, geniculate, occipital) waves
• Precursors to REM
• Acetylcholine secreted from dorsal pons
facilitates REM sleep
• Acetylcholinergic neurons in the
peripbrachial area of pons
• show high activity during REM and/or
awake activity
• REM disrupted if lesioned
• Project axons to
• Forebrain structures
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Psyc 372 – Physiological Psychology
Functions of Sleep
• Conserve energy during parts of day
that are less productive (diurnal vs.
nocturnal animals)
• Preserve and restore brain functioning
• deep sleep (stages 3-4)
• eliminates free radicals
• Learning and memory consolidation
• REM, dreaming, and the daily residue
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