Infradian Rhythms

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

• 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

• UNDERMINES
• 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

• SUPPORTS
• 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

• UNDERMINES
• 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

• SUPPORTS
• 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

• SUPPORTS
• 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