infradian rythms Flashcards
what are infradian rhythms
less than one cycle every 24 hours
infra = below
what occurs during the female menstrual cycle
During the menstrual cycle, rising levels of the hormone oestrogen cause the ovary to develop and release an egg (ovulation). Ovulation occurs half way through the menstrual cycle when oestrogen levels are highest. Then progesterone helps the womb lining to thicken, readying the womb for pregnancy. If pregnancy does not occur, the egg is absorbed and womb lining comes away.
what is menstrual synchrony
menstrual synchrony, also called the McClintock effect is when women who live together in close proximity experience synchronised menstrual cycles
research which shows how the menstrual cycle can be affected by external cues
Stern and McClintock studied 29 women with irregular ovulation in a 10 year longitudinal study/
Pheromones were taken from 9 at different stages of their cycles via a cotton wool pad under their armpits. These were then places under the noses of the 20 other women on a daily basis.
68% of the women experienced changes to their cycle which brought them closer to the cycle of their ‘odour donor’.
Their menstrual cycles became synchronised to their pheromone donors. The pheromones acted as exogenous zeitgebers and modified the women’s infradian rhythm of menstruation.
strength of research on menstrual cycle (shows evolutionary basis)
In our evolutionary past, menstrual synchrony between women would mean that females get pregnant at this same time. This is advantageous as this would allow babies who have lost their mothers to have access to breast milk, thereby improving the chances of survival.
supporting evidence from McClintock
Found that women who work with men had much shorter menstrual cycles. This suggests that male pheromones reset a woman’s biological clock and increases ovulation. This may have had an evolutionary adaptive function, as more frequent ovulation would increase the chances of reproduction and pregnancy.
limitation of synchronisation studies (methodology)
There are many factors that may change a womans menstrual cycle and act as confounding variables. eg stress, changes in diet.
Any supposed pattern may occur by chance, which may mean why researchers who have replicated McClintock’s study have not found the same results.
This suggests that menstrual synchrony studies are flawed.
SAD as an infradian rhythm
SAD - season affective disorder is a depressive disorder with a seasonal pattern.
Symptoms are triggered during the winter months when the number of daylight hours becomes shorter
SAD process
during the night, the pineal gland secretes more melatonin until dawn when there is an increase in light. In winter, less light means secretion goes on for longer. This has a knock on effect on the production of serotonin in the brain because melotonin is produced from serotonin (low levels linked to depression).
1. Lack of light
2. Pineal gland produces melatonin
3. Reduction in serotonin
4. Depression
strength of SAD as an infradian rhythm (real world application)
Understanding the role of darkness in SAD has lead to effective therapies, most notably phototherapy (light therapy). This uses strong lights in the morning to change levels of melatonin and serotonin.
SAD sufferers have reported that daily use of phototherapy has helped to improve feelings of depression and other related symptoms.
weakness (placebos)
The placebo effect could be at work in measuring the effects of phototherapy. One study found that 52% of pp’s reported improvement with the placebo alone which questions its effectiveness. The problem could be more psychological then for some than others.
