ULTRADIAN RHYTHMS

• A type of biological rhythm which has a duration of less than 24 hours, such as the cycle of sleep stages that occur throughout the night. 
• Sleep cycle


  Five stages have been identified and the cycle repeats itself about every 90-100 minutes throughout the night. Most of what we know about the sleep cycle comes from the recording of electrical activities in the brain, with each stage showing a specific EEG pattern. 
• 5 stages of sleep

  Stage 1 – light sleep that is easily woken up from – brain waves are slower 

  Stage 2 – high frequency waves called ‘sleep spindles’ - still very easily woken from 

  Stage 3+4 – brain waves start to slow and become higher in amplitude and wavelength – called delta waves and are associated with deep sleep 

  Stage 5 (REM sleep) – fast activity of eye under the eyelid – associated with dreaming and deep sleep. Heart rate and blood pressure increase as well as body temperature 
• Strength

  ✅Supporting evidence – a study showed that REM sleep was highly correlated with the experience of dreaming and participants woken up during this stage reported a very accurate recall of their dream – suggests REM stage is a distinct place where dreaming occurs, and this increases the reliability. 
• Limitation

  ❌Significant variation between people – biologically determined differences between participants in terms of the duration of each sleep stage particularly stage 3 and 4 - difficult to describe ‘normal sleep’.