Ultradian Rhythms

• Ultradian Rhythm - consistent cyclical variations over a period of less than 24 hours.

  An example would be slow wave/REM rhythms occurring during a sleep cycle.
• Sleep cycle

  A typical adult will have 4-5 sleep cycles that last around 90 minutes each night. These cycles begin with NREM (slow wave sleep) and are followed by Rapid Eye Movement Sleep. Each sleep stage is characterised by a different level of brainwave activity which can be monitored using EEG.
• The sleep cycle:

  Stage 1 - sleeper is easily woken and may feel that they have not slept. May last for 5 to 10 minutes.

  Stage 2 - sleeper is a bit harder to awake. Usually lasts 20 minutes. Readings show some bursts of activity called sleep spindles. Heart rate slows and body temperature decreases as the body prepares to enter deep sleep.
• The sleep cycle stages 3 and 4:

  Stage 3 and 4 - deep sleep stages. Known as slow wave sleep because of low frequency and high amplitude. Muscles are very relaxed and sleeper is hard to awake. Body temp and blood pressure are at there lowest. Sleep walking and talking occur in this stage.

  Stage 5 - REM sleep, rapid eye movements. Heart rate and respiration speed up and become erratic. Intense dreaming occurs. Brain is very active.
• Research - sleep lab studies

  Participant is wired up to a Polysomnograph.

  The participant then goes to sleep in the lab and all these functions are recorded.

  Usually the participant spends several nights in the sleep lab.

  In the Dement study, 9 participants were studied up to 61 nights in a lab
• Evaluation of Sleep lab studies -

  Polysomnographs have been indispensable in studying sleep. They are controlled studies giving objective, unbiased findings.

  The findings are reliable having been replicated so many times.

  However, sleeping in the lab wired up in this way is artificial and sleep patterns may differ from normal.
• Animal studies - Jouvet

  Lesioned the raphe nucleus in cats and found that this resulted in sleeplessness.

  Lesioning the locus coerlus resulted in a loss of REM sleep

  These appear to be the endogenous factors involved in REM/NREM ultradian rhythm.
• Evaluation - animal studies

  Provides invaluable evidence to suggest that the raphe nucleus and locus coerlueus are the endogenous factors which control the NREM/REM sleep cycle.

  Controlled scientific procedures were used which have been replicated by other researchers.

  The observed effects of the lesioning of the brain could partly be due to the trauma of surgery or damage to other areas of the brain.

  Ethical concerns