Infraradian and ultraradian rhythms Flashcards
What is an infradian rhythm?
A biological rhythm with a frequency of less than 1 cycle in 24 hours. This means a cycle may last a month, like the menstrual cycle, or a year like with Seasonal Affective Disorder.
Why is the menstrual cycle an infradian rhythm?
The typical cycle takes 28 days to complete as oestrogen causes the egg to develop and release. After ovulation, progesterone helped the womb lining to grow thicker and then if pregnancy doesn’t occur, the egg is absorbed back onto the body.
What study did McClintock do?
She studied 29 women with a history of irregular periods and pheromones were collected from 9 women by placing cotton pads under their armpits. The pads were rubbed on the lip of other participants and and 68% of women experienced changes in their cycle which bought it closer to the donor. This shows it may be influenced by exogenous factors.
What is SAD?
Seasonal affective disorder is a depressive disorder where symptoms are triggered during the winter months. It is a yearly cycle and psychologists have suggested that the long darkness leads to more melatonin production and then a reduction in serotonin.
What is an ultradian rhythm?
A biological rhythm with a frequency of more than one cycle in 24 hours. This means the cycle is less than 24 hours, for example the sleep cycle.
What happens in the sleep cycle?
The sleep cycle lasts around 90 minutes and has 5 stages. Stages 1 and 2 are light sleep with alpha and theta waves, Stages 3 and 4 involve delta waves and is deep sleep. Stage 5 is REM sleep where the body is paralysed.
What are the strengths of research into infradian and ultradian rhythms?
Menstrual synchrony has evolutionary advantages as children could be cared for collectively within a group.
There is evidence to support the different stages of sleep as EEGs have been used to record brain activity and REM activity has been strongly correlated with dreaming.
There is practical application of treating SAD based on the infradian cycle. Phototherapy involves a strong light in the morning and evening and 60% of suffers had reduced symptoms.
What are the issues of research into ultradian and infradian rhythms?
Menstrual synchrony could produce competition for men and so it could be argues that avoiding synchrony would be better, meaning the research may not be valid.
There are limitations of the methodology of synchronisation studies as stress and changes in diet may act as confounding variables. Other studies have failed to find any evidence.
Much of our knowledge comes from research into animals and pheromones. These findings are often very difficult to generalise to humans.
