biological rhythms: infradian and ultradian rhythms Flashcards
what are infradian rhythms?
are a biological rhythm with a frequency of less than one cycle every 24 hours (e.g. the menstrual cycle and seasonal affective disorder)
what is the menstrual cycle?
it takes approximately 28 days to complete where during the cycle, the rising levels of the hormone oestrogen causes the ovary to develop and release an egg. After ovulation, progesterone causes the womb lining to thicken readying the body for pregnancy. If the pregnancy does not occur, the womb lining leaves the body (menstrual flow)
what is seasonal affective disorder?
this is a depressive disorder where the main symptoms include persistent low mood, lack of activity and interest in life. it is also known as the ‘winter blues’ and is triggered by shorter daylight hours. During the night the pineal gland secretes the hormone melatonin which makes us tired. During the winter months this secretion continues for longer which has a knock-on effect with the production of serotonin where low levels of serotonin lead to depressive symptoms.
what did Martha McClintock investigate into menstrual cycles and infradian rhythms?
she investigated whether women who live together experience menstrual synchrony.
what was McClintocks method into her research of menstrual synchrony?
she looked into 135 college women living in dormitories and she studied the menstrual cycle of 29 women over a period of several months. McClintock collected data from the onset of their menstrual cycle and during their cycles. The key variable examined was the timing of menstruation. McClintock hypothesised that women who spend a lot of time together might experience synchrony in their menstrual cycles due to close social interaction. To collect data, she observed the timing of menstruation, comparing the onset of periods among the women at different points during the study.
what were McClintocks findings into her research into menstrual synchrony?
she found that women’s menstrual cycles appeared to synchronise over time. Specifically the women who were living in close proximity to each other had periods that gradually became more aligned.
what are ultradian rhythms?
are a biological rhythm with a frequency of more than one cycle every 24 hours (e.g. stages of sleep)
what are the stages of sleep?
the stages of sleep follow an ultradian rhythm of 90 minutes where we move between NREM sleep and REM sleep. This movement is linked with the basic rest and activity cycle. This suggests that we move through a similar cycle of alertness and fatigue during the day. For example, research suggests that we can concentrate for approximately 90 minutes before we begin to lose concentration and begin to feel hungry and fatigued.
what are the 5 stages of the sleep cycle?
Stage 1- theta waves
Stage 2- light sleep
Stage 3+4- delta waves
Stage 5- REM sleep
AO3: how is ‘evolutionary advantages’ a strength to research into infradian rhythms?
one strength to infradian rhythms and research into menstrual synchrony is that it can be explained through natural selection. This is because the synchronisation of the menstrual cycle is thought to have some evolutionary value. For example, our distant ancestors would’ve benefited from menstruating together and becoming pregnant at the same time. This is because it would allow babies who lost their mothers during childbirth to have access to breast milk and therefore a higher chance of surviving. Therefore, this supports the idea that synchronisation is an adaptive strategy.
AO3: how is ‘methodical issues’ a limitation to research into infradian rhythms?
one limitation to research into infradian rhythms is their methodical factors. This is because there are many factors that may influence the menstrual cycle such as stress, exercise and any changes in our diet. These factors can also be classed as confounding variables meaning any supposed pattern of synchronisation is no more than what would have been expected to happen by chance. This helps us to understand why other studies have failed to replicate the findings found within this study. Therefore, this suggests that the findings within the menstrual synchrony studies are flawed and that the research findings suggest a correlation meaning they are unable to claim causation.
AO3: how is ‘real life application’ a strength to research into infradian rhythms?
one strength to research into infradian rhythms is that it can be applied to real life. For example, by understanding seasonal affective disorder, researchers have created therapies such as light therapy which has proven to be successful. This is where a light box stimulates very strong light to reset the bodies internal clock and this has been proven to reduce the effect of seasonal affective disorder in 80% of patients. Therefore, this treatment is preferred over drug treatments due to it being regarded as safe. However, light therapy can cause headaches and eye strain and other research has found there to be a 46% relapse rate over winters compared to a CBT group who had a relapse rate of 27% suggesting that other therapies may be more effective in the long term.
AO3: how is ‘improved our understanding of sleep cycles’ a strength to research into ultradian rhythms?
one strength of research into ultradian rhythms is that it has helped us to understand age-related changes in sleep. This is because sleep scientists have observed that slow-wave sleep reduces with age and that the growth hormone is usually produced during this period which in older people is reduced. For example, Eve van Cauter suggested that the resulting sleep deficit may explain various issues in old age such as reduced alertness. From this, researchers have found that in order to increase the SWS, relaxation techniques such as meditation can be used. Therefore, this suggests that by understanding ultradian rhythms, it can be used in practical settings.
AO3: how is ‘individual differences’ a limitation to research into ultradian rhythms?
one limitation to research into ultradian rhythms is that there are significant variations between individuals. This is because there are many different variables within a person’s life that may effect there ability to go to sleep and to stay asleep. For example, Tucker et al found that there were large differences between participants in terms of the duration of each sleep stage, particularly stages 3 and 4. He suggested that these differences within the sleep are most likely to be biologically determined. Therefore, this suggests that we are unable to describe what normal sleep is in any meaningful way.
