Infradian Rhythms

Infradian Rhythms, AO1 and AO2

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AO1 - Female Menstrual Cycle

Infradian Rhythms are biological rhythms that last longer than 24 hours

Example of an infradian rhythm = female menstrual cycle

  • Pituitary gland releases FSH and LH
  • Stimulates a follicle in one ovary to ripen an egg + triggers oestrogen
  • Ruptured follicle secretes progesterone
  • Lining of womb prepares for pregnancy - increases blood supply
  • If there is no pregnancy, progesterone is reduced
  • Lining of womb is shed
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AO1 - Seasonal Affective Disorder

  • Another example of an infradian rhythm
  • Some people suffer from this depressive condition, which leads them to become depressed during the winter months and recover during the summer
  • SAD sufferers exhibit severe depressive symptoms, including persistent low mood and suicidal thoughts
  • It is caused by serotonin and melatonin levels
  • Serotonin is created in the light and then makes melatonin in the dark
  • When it is dark outside, there is less serotonin to boost your mood
  • The serotonin you do have goes into making melatonin, leaving you feeling persistently tired and low
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AO2 - Exogenous Cues for Menstruation

  • The menstrual cycle is usually governed by an endogenous system - the release of hormones under the control of the pituitary gland
  • However, it can also be affected by exogenous cues
  • Russel et al: carried out a lab experiment with a woman who had a history of a very regular menstrual cycle, and of influencing those of other women
  • They did not permit her to wash under her arms for several days, and collected sweat from here on cotton pads
  • These sweat samples were then rubbed on the upper lips of a group of women every few days for a month
  • The women were not permitted to wash their faces for six hours
  • Their menstrual cycles became synchronised with the donor's, despite having no other contact with her than this
  • The pheromones released in her sweat had an effect on the other women's bodies
  • This shows that infradian rhythms can be altered by exogenous cues
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AO2 - Consequences of the Menstrual Cycle

  • PMS is a disorder that affects many women the week before menstruation begins, when progesterone rises
  • Symptoms can include aggression, anxiety and depression, insomnia, mood swings
  • For many years it was dismissed as a psychological problem but now we know that it is a physiological problem with psychological symptoms
  • It is caused mainly by hormonal changes related to the infradian rhythm
  • This demonstrates the reality of infradian rhythms
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  • SAD has been explained as a natural outcome of infradian rhythms, but it could be the consequence of a disrupted circadian rhythm
  • In the UK, as the seasons change from summer to winter, the circadian rhythms may be thrown out of phase
  • People continue to get up at about the same time but often go to bed earlier because it is darker earlier
  • The biological system gets the impression that time is shifting and the result is similar to jet lag
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IDA - A Determinist Approach

  • Dalton: PMS is associated with an increase in accidents, lower achievement academically, suicides, and crime
  • PMS has been used as a legal defence: a Ms English drove her car into her married lover after an argument, killing him
  • She was charged with murder but placed on probation because it was argued in court that her actions were related to severe PMS
  • Dalton: argued that severe PMS was akin to a mental disorder and therefore individuals must not be held responsible for their actions
  • This suggests that biological rhythms may be beyond our control
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IDA - Real-World Applications

  • This understanding of the role of darkness in SAD has led to the development of effective therapies, including phototherapy
  • This uses very strong lights in the evening and/or early morning to change levels of serotonin and melatonin
  • SAD sufferers have reported that the daily use of these light boxes is enough to relieve them of their feelings of lethargy and depression
  • HOWEVER this may be due to a placebo effect
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