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Infradian and Ultradian rhythms 16 markers
A*/A grade 16 mark model answer on Infradian and Ultradian rhythms (AQA A-level Psychology)
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Infradian and ultradian rhythms 16 markersUltradian rhythms are biological rhythms that are shorter than 24 hours for example the five
stages of sleep. This cycle alternates between REM sleep and NREM sleep (rapid and non-
rapid eye movement) and repeats every 90 minutes five times.
Infradian rhythms are biological rhythms which are greater than 24 hours for example the
female menstrual cycle and SAD (seasonal affective disorder). The female menstrual cycle is
regulated by hormones such as progesterone and oestrogen that effect ovulation, the entire
cycle lasts for 28 days before an egg is released. And SAD disorder is a yearly cycle related to
the seasons as longer nights in winter more melatonin is secreted by the pineal gland, which
is linked to suppressive symptoms.
One positive of research into ultradian rhythms specifically SAD is that it has led to
important practical applications. For example, light boxes which in the morning stimulates
the reset of melatonin and relieves symptoms of 60% of SAD suffers, which was made
possible by understanding how the ultradian rhythm works. However, it’s extremely
possible that these results were the product of the placebo effect. This is because sham
negative-ion generators produced similar results. So, doubt is cast over whether the
practical applications actually do anything, even if they are placebo, they still relieve
symptoms and suggest the impact of exogenous zeitgebers on SAD.
There is some evidence that suggests that exogenous zeitgebers can also affect infradian
rhythms. McClinctok 1998 synchronised 29 women’s periods using pheromones. This
suggests that menstrual cycles can be influenced by external factors, and a more holistic
approach should be taken when observing infradian rhythms as opposed to a reductionist
approach that only considers endogenous influences.
However, one negative about the research conducted by McClinctok was that he had no
way to control the confounding variables. As other factors such as stress, diet or exercise
may influence the infradian rhythm, and it may have just been chance that the women’s
period synced. Decreasing the validity of the effect of pheromones on the menstrual cycle.
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