Ultradian Rhythms

Ultradian Rhythms, AO1 and AO2

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AO1 - Sleep Stages 1

  • Ultradian rhythms are biological rhythms that last less than 24 hours
  • Researchers have identified 5 distinct 90-minute stages of sleep

Stages 1 and 2 (NREM)

  • Relaxed state, easily woken
  • Slow alpha and theta waves, accompanied by bursts of activity (sleep spindles) and increased wave amplitude (k complexes)
  • Heart rate slows, temperature drops

Stages 3 and 4 (NREM)

  • Delta waves, metabolic rate slowest
  • Hard to wake them up, but not unconscious
  • Physiological 'repair work' takes place
  • Growth hormone produced
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AO1 - Sleep Stages 2

REM (a.k.a Stage 5)

  • Fast, desynchronised EEG activity resembling the awake brain
  • Rapid eye moments (which is where it gets its name from)
  • Called 'paradoxical sleep' because brain and eyes are active but body is paralysed
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AO2 - Basic Rest-Activity Cycle

  • SUPPORTS
  • Researcher have found that the 90-minute 'clock' is also ticking throughout the day
  • It is called the basic rest-activity cycle
  • Friedman and Fisher: observed eating and drinking in a group of psychiatric patients over periods of six hours
  • Detected a clear 90-minute cycle in eating and drinking behaviour
  • Shows that ultradian rhythms do exist and not just in sleep
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AO2 - REM sleep and Dreams 1

  • UNDERMINES
  • An issue with studies on REM sleep is the assumption that it is for dreams
  • Dement and Kleitman: woke participants up at times when their brain waves were characteristic of REM
  • They were highly likely to report dreaming
  • HOWEVER, dreams were also recorded outside of REM sleep
  • When awoken in REM, sleepers were not always dreaming
  • Questions the ecological validity of the experiments
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AO2 - REM sleep and Dreams 2

  • UNDERMINES
  • The importance of the REM-dream link is that it potentially provides a way to identify when someone is dreaming
  • It therefore might provide theorists with a way to explain dreaming
  • Hobson and McCarely: proposed that dreams are just a psychological read-out of the random electrical signals typical of REM sleep
  • Such theories are based on the erroneous assumption that REM activity = dreaming
  • Which, as has previously been noted, is not the case
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AO2 - Support for the BRAC

  • SUPPORTS
  • The BRAC shows that sleep stages are part of a continuum: a 90-minute cycle that occurs throughout the day within the circadian rhythm
  • The importance of this 90-minute rhythm is probably as a form of timing to ensure that biological processes in the body work in unison
  • Much like how a conductor keeps time in an orchestra
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