Rhythms of the Brain

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Rhythms of the Brain
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Types of Rhythms

• Circadian fluctuate daily
• Sleep-wake, temperature, hormones, urine
  production, gastrointestinal activity
• Cognitive and motor performance levels
• Infradian less than once a day
• Hibernation, ovulation
• Ultradian more than once a day
• Sleep cycles (REM and other sleep stages)

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How do they do it?

• 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.

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Environmental Cues

• Biological clock overrides most environmental
  cues.
• Some cues (Zeitgebers) are used
• Temperature
• Light
• Temperature doesnt make squirrels hibernate.

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Three Steps to Regulation

• Input senses light or temperature.
• Pacemaker generates and regulates the rhythm
  e.g., thalamic pacemaker.
• Also, rhythmic activity may arise from the
  collective behavior of inhibitory and excitatory
  neurons.
• Output permits pacemaker to affect tissues and
  organs.

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Bird Biological Clock

• 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).
• N-acetyltransferase is key to this process
• Output melatonin released to bloodstream to
  affect organs.

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Human Biological Clock

• 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).

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Multiple Pacemakers

• SCN cycles (affected by environment)
• Sleep-wake cycles
• Skin temperature
• Hormones in blood, calcium in urine.
• Cycles independent of SCN
• Sleep cycles (REM)
• Internal body temperature
• Cortisol in blood, potassium in urine.

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Ultradian Rhythms

• Humans cycle through an alertness and cognitive
  performance cycle every 90 to 100 minutes
  throughout the day.
• Research into such rhythms is just beginning.

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Sleep

• A readily reversible state of reduced
  responsiveness to, and interaction with, the
  environment.
• Lack of sleep produces unpleasant symptoms.
• Irritability, impaired performance on cognitive
  tasks, no lasting effects on physical health.
• Sleep debt
• Why we sleep
• Restoration or adaptation?

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Human Sleep-Wake Cycles

• 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.
• Change to local schedule immediately

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How Long People Sleep

• 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.

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Types of EEG Rhythms

• Frequency is measured in Hz
• Four types
• Beta (gt14 Hz) thinking (active cortex)
• Alpha (8-13 Hz) quiet waking states
• Theta (4-7 Hz) present during first stage of
  sleep.
• Delta (lt4 Hz) present during deep sleep

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Sleep Cycles

• Five stages
• 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)

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Stages (Cont.)

• Non-REM sleep
• Less dreaming
• Ability to move muscles
• Sympathetic ANS inactive
• No impact on learning with deprivation
• REM sleep
• Most dreaming
• Atonia inability to move muscles
• Sympathetic ANS active
• Learning is affected by deprivation

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Control of Sleep Cycles

• Diffuse modulatory systems control sleep and
  waking (locus coeruleus).
• 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.

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Control of Sleep (Cont.)

• 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.

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What is Dreaming?

• Activation-synthesis hypothesis
• Dreams are associations and memories elicited by
  pontine neurons via thalamus
• The cortex tries to synthesize this random
  activity into something meaningful.
• Consolidation hypothesis
• REM sleep aids integration and consolidation of
  memories.
• Sleep learning is bogus.

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Rhythms and Disturbance

• Epilepsy
• Delayed sleep-phase insomnia
• Seasonal depression

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Epileptic Seizures

• Extreme synchronous behavior in which many
  neurons fire at once.
• Localized or global
• Upsets balance of excitation and inhibition among
  neurons
• Anticonvulsants drugs that counter excitability
  of neurons.
• Convulsants drugs that block GABA.

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Delayed Sleep-Phase Insomnia

• 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 peoples schedules.

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Seasonal Depression

• Desynchronization between circadian rhythms,
  sleep and emotion states may result in
  depression.
• Depression is almost invariably cyclic.
• Many depressed people enter REM sleep earlier
  than normal.
• Sleep deprivation may ease depression temporarily.