Infradian Rhythms

• Infradian Rhythms


  • Biorhythms with a frequency of less than one cycle in 24 hours - less frequently than daily (gap longer than a day) (more than a day to complete)
  • It takes longer than 24 hours to complete. More frequent vs Ultradian
  • e.g. menstrual cycle.
• For example Infradian Rhythm?


  • The female menstrual cycle is an infradian rhythm
  • SAD
• Menstrual Cycle


  The female menstrual cycle is an infradian rhythm:

  Menstrual Cycle:

  • The human female menstrual cycle is typically about 28 days (i.e. less than one cycle in 24 hours - infra diem meaning ‘below’ a day)(could be anything from 24-35).
  • Starts 1st day of period and ends the day before the next period.
  • Rise in oestrogen levels cause ovary to develop then release an egg (ovulation)
  • Progesterone allows womb lining to grow thicker in preparation for pregnancy.
  • If this does not occur then the egg is absorbed and the womb lining comes away (menstrual flow).
• People who studied menstrual cycles, aim & procedure?

  Stern & McClintock (1998):

  Aim: To investigate whether the menstrual cycle is completely endogenous.

  Procedure: 29 women with a history of irregular period cycles were provided pheromone samples on cotton pads to be placed on their upper lips.

  These samples were provided by 9 of the women who were at various stages of their cycle and were collected from pads placed under their armpits.

  These pads were cleaned with alcohol and later rubbed on the upper lips of the other participants.

  This was repeated everyday of the cycle.
• Studying the menstrual Cycle - findings & conclusion?

  Stern & McClintock (1998):

  Findings: 68% women experience changes to their cycle which brought them closer to cycle of their ‘odour donor’.

  Conclusion: Menstrual cycle affected not just by hormones (endogenous) but also by exogenous zeitgebers (pheromones).

  Findings suggest infradian rhythms like menstrual cycle are not completely determined by endogenous pacemakers like hormones but may be entrained by exogenous zeitgebers like pheromones of other females in close proximity.

  Exogenous zeitgebers may synchronise menstrual cycles:
• SAD - what, rhythm, symptoms, when?


  • Seasonal Affective Disorder is a depressive disorder which has a seasonal pattern of onset. SAD is an infradian rhythm as it is subject to a yearly cycle.
  • As with other forms of depression the main symptoms of SAD are persistent low mood alongside a general lack of activity and jot in life.
  • SAD is often referred to as the ‘winter blues’ as the symptoms are triggered during the winter months when the number of daylight hours become shorter. 
• What cycle is SAD?


  • SAD is an infradian rhythm as it is subject to a yearly cycle. However, it can also be classed as a circadian rhythm as the experience of SAD may be due to the disruption of the sleep/wake cycle and this can be attributed to prolonged periods of daily darkness during winter.
• What causes SAD?


  • Psychologists hypothesised the hormone melatonin is implicated in case of SAD. 
  • During night, pineal gland secretes melatonin until dawn when there is an increase in light.
  •  During winter, the lack of light in the morning (less light overall in winter) means the melatonin secretion continues for longer. 
  • This is thought to have a knock on effect on the production of serotonin in the brain - a chemical that had been linked to the onset of depressive symptoms. (low serotonin is linked to depressive symptoms).
  • (Melatonin and serotonin can not be produced at the same time)
• What do you need to know about SAD?


  • What it stand for
• What do you need to know about SAD?


  • What it stands for
  • What it is
  • When it occurs
  • Symptoms
  • Type of cycle
  • Why it occurs