Ultradian Rhythms and Ifradian Rhythms

• What is the duration of infradian rhythms?

  Longer than 24 hours
• What is the duration of ultradian rhythms?

  Under 24 hours
• What are examples of infradian rhythms?

  • Menstrual cycle
  • Seasonal Affective Disorder (SAD)
  • Hibernation in animals
• What is the typical length of the menstrual cycle?

  Typically 28 days
• How long can women's menstrual cycles vary?

  Between 23 to 25 days
• What regulates the menstrual cycle?

  Hormones that stimulate or cease ovulation
• When does ovulation occur in the menstrual cycle?

  Halfway through the cycle
• What happens to progesterone levels after ovulation?

  Progesterone levels increase
• How is the infradian rhythm related to seasons?


  It can be related to a yearly cycle
• What hormone is secreted by the pineal gland at night?

  Melatonin
• What effect do longer nights have on melatonin levels?

  Increased melatonin secretion
• What is melatonin linked to in terms of mental health?

  Depressive symptoms
• How long can infradian rhythms last?

  They can last weekly, monthly, or yearly
• McClintock Study -

  • 29 women from same college dorm
  • Pheromones taken from 9 women who had cotton pad under their armpit for 9 hours
  • Rubbed on upper lip of the other women at different stages of their menstrual cycle
• McClintock found that 68% of the women’s menstrual cycles were linked up to the women’s pheromones they had than before the study
• pheromones are an exogenous zeitgebers that can influence the menstrual cycle
• Limitation of McClintock’ study - Research found that pheromones do not affect menstrual cycles of women living in same dorm
• Sleep is divided into Non-REM sleep and REM sleep
• What is the cycle duration of ultradian rhythms?

  It repeats every 90 minutes
• How many times does the ultradian rhythm cycle repeat on average in a 24-hour period?

  5 times
• What are the stages of sleep in the ultradian rhythm?

  • Stages 1 + 2 (Alpha and Theta) : Light sleep - slow brain patterns
  • Stages 3+4 (Delta): Deep sleep - also known as slow wave sleep
  • Stage 5: REM sleep - desynchronized brain waves
• What characterizes REM sleep in the context of ultradian rhythms?

  It features desynchronized brain waves
• How often do ultradian rhythms occur within a 24-hour period?

  Several times
• Dement and Kleitman -

  • 9 participants in study (7 male and 2 female)
  • Allowed to eat normally but no caffeine or alcohol
  • When woken during Non-REM sleep they could recall 7% of dreams compared to 80% during REM
• Research has been criticised for using small samples high makes it difficult to generalise to population
• Research has also been criticised for artificial settings - different bed to normal, electrodes attached to scalp and being aware of being watched