infradian and ultradian rhythms

• infradian 


  typical biological rhythm- less than 1 cycle in 24 hours e.g., menstruation
• ultradian 


  typical biological rhythm- more than 1 cycle in 24 hours e.g., stages of sleep
• menstrual cycle 


  • infradian
  • typical cycle- 28 days to complete
• seasonal affect


  form of depression triggered in the winter months + regulated by melatonin- circannual rhythm
• stages of sleep (ultradian)


  • occur in 90 minute cycle
  • stages 1+ 2= alpha and theta waves
  • stages 3+4= deep sleep, delta waves
  • stages 5= REM sleep
• strength: evolutionary basis of menstrual cycle 


  • synchronised may have an adaptive function because newborns cared for collectively
  • this would also produce competition for fittest males
• weakness: methological issues in synchronisation studies


  • many cofounding factors not controlled e.g., stress, diet
  • small samples
• strength: evidence supports the idea of distinct stages in sleep

  • Deement + kleitman using EEGs showed how REM (dream) sleep is an important sleep cycle