Biological Rhythms: Infradian And Ultradian Flashcards
What are infradian rhythms?
A type of biological rhythm with a frequency of less than one cycle in 24 hours such as the menstrual cycle and seasonal affective disorder (SAD)
Explain how the female menstrual cycle is an example of an infradian rhythm?
The female menstrual cycle is governed by monthly changes in hormone levels which regulate ovulation- the typical cycle takes on average, 28 days to complete so is an infradian rhythm
Describe the role of oestrogen and progesterone in the female menstrual cycle
During each cycle, rising levels of oestrogen cause the ovary to develop and release a mature ovum (ovulation). After ovulation, the hormone progesterone helps the womb lining to thicken, readying the body for pregnancy. If fertilisation does not occur (and thus pregnancy) the egg disintegrates and the womb lining comes away (sheds) and leaves the body (menstrual flow)
Explain a study which suggests that menstrual cycles can be synchronised due to exogenous zeitgebers
Stern and McClintock’s (1998) study involved 29 women with a history of irregular periods. Samples of pheromones were taken from 9 of the women at different stages of their cycle, via a cotton pad placed under their armpit. The pads were rubbed on the upper lip of the other participants. On day 1, pads from the start of the menstrual cycle were applied to all 20 women, on day 2 they were all given a pad from the second day, and so on. 68% of women experienced changes to their cycle which brought them closer to their ‘odour donor’ = menstrual cycles may synchronise due to exogenous zeitgebers
What is seasonal affective disorder (SAD)?
Depressive disorder associated with seasonal changes- usually the onset of winter and increased darkness. As with other forms of depression, the main symptoms are persistent low mood, and a general lack of interest and activity in life e.g. avolition
Explain how SAD is an infradian rhythm
It is often referred to as the ‘winter blues’ because the symptoms are triggered during the winter months when the number of daylight hours becomes shorter. SAD is a particular type of infradian rhythm called a circannual rhythm as it is subject to a yearly cycle
Explain how the hormone melatonin is thought to be a causal factor of SAD
Psychologists have suggested that the hormone melatonin is implicated in the cause of SAD- during the night, the pineal gland secretes melatonin until dawn when there is an increase in light. During winter, the lack of light in the morning means this secretion process goes on for longer; this is thought to have a knock-on effect on the production of serotonin in the brain (low serotonin is linked to symptoms of depression)
What are ultradian rhythms?
A type of biological rhythm with a frequency of more than one cycle in 24 hours, such as the stages of sleep
Explain how stages of sleep are an example of ultradian rhythms
Psychologists have identified distinct stages of sleep that altogether span approximately 90 minutes- a cycle (ultradian rhythm) that continues throughout the course of the night. Each of these stages is characterised by a different level of brainwave activity which can be monitored using an EEG
The sleep stages collectively are often referred to as
The ‘sleep escalator’
Describe the 5 stages of sleep that have been identified
- stages 1 and 2 are light sleep where the person may easily be woken- at the beginning of sleep, brainwave patterns start to become slower and more rhythmic (alpha waves), becoming even more slower as sleep becomes deeper (beta waves)
- stages 3 and 4 involve delta waves which are slower still and have a greater amplitude than earlier wave patterns- this is deep sleep or slow wave sleep (sleep stage during which growth hormone is secreted as well as other restorative activities) and is very difficult to wake someone up at this point
- stage 5 = REM sleep, the body is paralysed yet brain activity speeds up significantly- REM stands for rapid eye movement to denote the fast, jerky activity of the eyes at this point. The EEG pattern resembles that of an awake person and it is in this stage that most dreaming occurs
What are the evaluation points for infradian and ultradian rhythms?
✅ strength of research into menstrual cycle is that it demonstrates its evolutionary value
❌ limitations of methodology used in synchronisation studies
❌ use of animal studies
✅ practical applications from research into SAD
Discuss how a strength of research into menstrual cycle is that it demonstrates its evolutionary value
For our ancestors it may have been advantageous for females to menstruate together and thus fall pregnant around the same time as this would mean that newborns could be cared for collectively, increasing the chances of the offspring’s survival.
HOWEVER
the validity of this evolutionary perspective has been questioned though. Schank (2004) has argued that JG there were too many females cycling together within a social group, this would produce competition for the highest quality males (lowering the fitness of potential offspring. So, from this point of view, the avoidance of synchrony would appear to be the most adaptive evolutionary strategy and therefore naturally selected
Discuss how there are limitations of the methodology used in synchronisation studies
Commentators argue that there are many factors that may effect change in a woman’s menstrual cycle including: stress, changes in diet, weight etc that may act as confounding variables. This means that any supposed pattern of synchronisation in studies like McClintock’s, is no more than would have been expected to occur by chance. In addition, research usually involves small samples of women and relies on on participants self-reporting the onset of their cycle (which may be inaccurate). Both possibile confounding variables and the reliance upon self-report techniques means that the methodology used in synchronisation studies may lack internal validity
Discuss how one limitation of research into infradian rhythms is the use of animal studies
Much of the knowledge of the effects of pheromones on behaviour is derived from animal studies and the role of pheromones in animal sexual behaviour is well-documented. For instance, sea urchins release pheromones into the surrounding water so other urchins will eject their sex cells simultaneously. However, evidence for the effect of pheromones on human behaviour remains speculative and inconclusive = drawing conclusions from animal studies alone might be invalid and at worst, it may be reductionist
