infradian rhythms

• infradian rhythm

  rhythm that has less than one cycle in 24hrs

  e.g. menstrual cycle, seasonal affective disorder
• menstrual cycle

  • governed by monthly changes in hormone levels.
  • typical cycle is 28 days long
• synchronising the menstrual cycle

  • evidence suggests it is influenced by exogenous factors.
  • Stern + McClintock's study
  • studied 29 women with a history of irregular periods.
  • samples of pheromones gathered from 9 of the women at different stages of their menstrual cycle via pads under their arm, worn for at least 8 hours.
  • pads were frozen and then rubbed on the upper lip of other participants.
  • founf that 68% of women experienced changes to their cycle which made them closer to the cycle of the donor.
• seasonal affective disorder

  • depressive disorder which has a seasonal pattern.
  • main symptoms = persistent low mood, lack of activity/interest in life.
  • referred to as 'winter blues'.
  • due to prolonged darkness of the days.
  • hypothesised to be due to the hormone melatonin
  • pineal gland secretes melatonin at night so during wnter longer nights means secretion is longer and has knock on effect on serotonin
• Strength - evolutionary basis

  • explained by natural selection
  • may have been beneficial for women to menstruate and be pregnant at the same time.
  • allows babies who lost their mothers to have access to breast milk.
• Limitation - methodological

  • confounding variables that may also effect the menstrual cycle
  • e.g. changes in diet, exercise
  • may explain why findings cannot be replicated.
  • could've been down to chance