ultradian rhythms

• Ultradian rhythm

  A biological rhythm that takes less than 24 hours to complete one cycle. The stages of sleep is one example.

  One sleep cycle takes about 90 minutes and repeats 4-5 times over the course of a night's sleep.

  The stages are identified by measuring distinctive brain wave patterns using EEG. Theta and Delta brain waves distinguish sleep stages.
• Sleep stages - stage 1

  (light sleep): Muscle activity slows down with occasional muscle twitching. A person can easily be woken. This typically lasts 10 minutes.
• Sleep stages - stage 2

  Breathing patterns and heart rate slows. There is a slight decrease in body temperature. The brain begins to produce bursts of rapid rhythmic brain waves (sleep spindles).
• Sleep stages - stage 3

  Deep sleep begins. The brain begins to generate slow delta waves. Your heartbeat and breathing slow to their lowest levels and your muscles are so relaxed that it may be hard to wake you.
• Sleep stages - stage 4

  Very deep sleep begins, with rhythmic breathing. There is limited muscle activity. It is difficult to wake someone at this point.
• Sleep stages - stage 5


  Rapid Eye Movement (REM) begins. Brainwaves speed up and dreaming occurs. Muscles relax and heart rate increased. Breathing is rapid and shallow. Activity here resembles and awake brain.
• / Small sample size often used in sleep studies


  E - For example, Dement and Klietman only used nine participants, all of whom were adults.

  E - This makes it difficult to take any meaning away from research as it cannot be applied across all individuals.

  L - Therefore, research can not be generalised as everyone experiences sleep in different ways.
• + Supporting evidence for sleep stages 


  E - Dermot and Kleitman: used EEG to record brain activity of 33 participants during one night's sleep. Brain waves followed a pattern resembling the sleep stages.

  E - This supports the theory that stages of sleep are an ultradian rhythm with distinct features at each stage.

  L - Therefore, the explanation of the sleep stages has high validity and can be generalised.
• + Practical applications


  E - Technology and devices based on understanding sleep stages have been developed.

  E - These track sleep and help individuals improve sleep - avoiding waking in stage 4 stops people from feeling disoriented.

  L - Therefore, this leads to a happier, healthier and more economically productive population.
• / Contradictory evidence


  E - Czeisler: found the longest period of REM sleep coincides with the lowest point in the circadian body temperature cycle.

  E - This suggests the circadian and ultradian rhythms are connected and perhaps shouldn't be considered as seperate processes.

  L - Therefore, the explanation for each rhythm may lack validity as they could both be combined.