Download November 29

Rhythms of the Brain
Types of Rhythms
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Circadian – fluctuate daily
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Infradian – less than once a day
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Sleep-wake, temperature, hormones,
urine production, gastrointestinal activity
Cognitive and motor performance levels
Hibernation, ovulation
Ultradian – more than once a day
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Sleep cycles (REM and other sleep stages)
How do they do it?
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Aplysia (sea slug) – neurons discharge faster
in light than in dark to regulate feeding.
Willow warblers – show migratory behavior
even when raised in the lab.
Squirrels – hibernate even when kept at a
constant temperature (below body).
Cycles appear to be genetic.
Environmental Cues
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Biological clock overrides most
environmental cues.
Some cues (Zeitgebers) are used:
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Temperature
Light
Temperature doesn’t make squirrels hibernate.
Three Steps to Regulation
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Input – senses light or temperature.
Pacemaker – generates and regulates the
rhythm – e.g., thalamic pacemaker.
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Also, rhythmic activity may arise from the
collective behavior of inhibitory and excitatory
neurons.
Output – permits pacemaker to affect tissues
and organs.
Bird Biological Clock
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Input = pineal gland – in birds and some
animals, located at the top of the skull to
sense light changes.
Pacemaker – tryptophan is converted to
melatonin (same process as serotonin).
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N-acetyltransferase is key to this process
Output = melatonin released to bloodstream to
affect organs.
Human Biological Clock
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Pineal gland unimportant to humans, but
melatonin may be important.
Information about light comes directly from
the retina to the suprachiasmatic nucleus
(SCN) in the hypothalamus.
SCNs generate rhythms (spontaneous firing).
Multiple Pacemakers
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SCN cycles (affected by environment):
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Sleep-wake cycles
Skin temperature
Hormones in blood, calcium in urine.
Cycles independent of SCN:
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Sleep cycles (REM)
Internal body temperature
Cortisol in blood, potassium in urine.
Ultradian Rhythms
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Humans cycle through an alertness and
cognitive performance cycle every 90 to
100 minutes throughout the day.
Research into such rhythms is just
beginning.
Sleep
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A readily reversible state of reduced
responsiveness to, and interaction with, the
environment.
Lack of sleep produces unpleasant symptoms.
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Irritability, impaired performance on cognitive
tasks, no lasting effects on physical health.
Sleep debt
Why we sleep:
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Restoration or adaptation?
Human Sleep-Wake Cycles
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Urine production decreases at night due to
fluctuations in vasopressin.
Sleep occurs instantaneously, not gradually.
Different people need different amounts of sleep. -no obvious relation to mental or physical activity.
Free of environmental cues (free running) people
adhere to a 24.8 hr day – mutant hamsters.
Jet lag occurs when sleep-wake cycles are out of
phase with environment.
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Change to local schedule immediately
How Long People Sleep
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Body temperature is highest in the afternoon
when people are active.
People sleep when body temperature is low
and wake when it is high.
Going to sleep when body temperature is high
results in longer sleeping times.
Feeling “dull” results from desynchronization
of sleep cycles.
Types of EEG Rhythms
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Frequency is measured in Hz
Four types:
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Beta (>14 Hz) – thinking (active cortex)
Alpha (8-13 Hz) – quiet waking states
Theta (4-7 Hz) – present during first stage of
sleep.
Delta (<4 Hz) – present during deep sleep
Sleep Cycles
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Five stages:
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Stage 1 – alpha rhythms (sitting quietly)
Stage 2 – theta rhythms (random neural activity)
Stage 3 – sleep spindles and K complexes
(synchronized bursts or neural activity)
Stage 4 – delta rhythms (marked slowing)
Stage 5 – REM sleep (rapid eye movement)
Stages (Cont.)
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Non-REM sleep:
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Less dreaming
Ability to move muscles
Sympathetic ANS inactive
No impact on learning with deprivation
REM sleep:
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Most dreaming
Atonia – inability to move muscles
Sympathetic ANS active
Learning is affected by deprivation
Control of Sleep Cycles
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Diffuse modulatory systems control sleep and
waking (locus coeruleus).
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Also control thalamus to synchronize brain waves
during sleep.
NE and Serotonin active during waking
enhance activity.
Different ACh neurons active in Pons during
REM sleep.
Control of Sleep (Cont.)
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Sleep-related rhythms from the thalamus
block sensory information to the cortex.
Activity in descending modulatory systems
inhibits motor neurons during dreaming
(REM sleep).
Sleep-promoting substances in blood related
to immune system stimulation – this is why
we sleep more when sick.
What is Dreaming?
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Activation-synthesis hypothesis:
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Consolidation hypothesis:
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Dreams are associations and memories elicited by pontine
neurons via thalamus
The cortex tries to synthesize this random activity into
something meaningful.
REM sleep aids integration and consolidation of
memories.
Sleep learning is bogus.
Rhythms and Disturbance
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Epilepsy
Delayed sleep-phase insomnia
Seasonal depression
Epileptic Seizures
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Extreme synchronous behavior in which many
neurons fire at once.
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Localized or global
Upsets balance of excitation and inhibition
among neurons
Anticonvulsants – drugs that counter
excitability of neurons.
Convulsants – drugs that block GABA.
Delayed Sleep-Phase Insomnia
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Sleep soundly for 8 or more hours but have
trouble getting to sleep in the first place.
Wake with difficulty and feel sleepy if forced
to conform to a normal schedule.
Goal is to resynchronize internal clock with
other people’s schedules.
Seasonal Depression
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Desynchronization between circadian
rhythms, sleep and emotion states may result
in depression.
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Depression is almost invariably cyclic.
Many depressed people enter REM sleep earlier
than normal.
Sleep deprivation may ease depression
temporarily.