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John Usher (30)

Brain Mechanisms of Sleep.docx

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PSYC 3325
John Usher

Brain Mechanisms of Sleep ● several brain regions have special roles in sleep and biological rhythms ● all living organisms show rhythmic changes in their physiological processes and behaviour – some of these rhythms are simply responses to environmental changes ● mammals have two biological clocks that play role in sleep ● circadian rhythms – daily rhythmical change in behaviour or physiological process; oscillates once a day ● second clock controls cycles of slow-wave and REM sleep, oscillates several times a day ● clock that controls circadian rhythms is located in small pair of structures located at bottom of hypothalamus: the suprachiasmatic nuclei (SCN)  activity of neurons in SCN oscialltes once each day; neurons are active during day and inactive at night  changes in activity control daily cycles of sleep and wakefulness  if person is kept in room with constant light their circadian rhythms will eventually get out of synch but will be back in sych within a few days of being outside ■ resynchronization is accomplished by direct connection between eyes and SCN ■ each morning when we see light our biological clock resets ● second biological clock in mammalian brain runs faster and continuously, unaffected by periods of light and darkness  in humans it cycles on 90 minute period ■ first suggestion that 90 minute cycle occurs throughout day came from observation that infants who are fed on demand show regular feeding cycles ■ later studies found 90 minute cycles of rest and activity, including such activities as eating, drinking, smoking, heart rate, oxygen consumption, stomach motility, urine production, and performance on tasks that make demands on person's ability to pay attention ■ basic rest-activity cycle (BRAC) – 90 minute cycle (in humans) of waxing and waning alterness controlled by biological clock in pons; duirng sleep it control cycles of REM sleep and slow-wave sleep; term coined by Kleitman  pons also contains neural circuits that are responsible for REM – neurons that begin a period of REM sleep release acetylcholine 
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