infradian rhythms Flashcards
what is an infradian rhythm?
rhythms that last longer than 24 hours, and can be weekly, monthly or annually.
what is an example of an infradian rhythm?
the female menstrual cycle. as it is governed by monthly changes in hormone levels which regulate ovulation.
although the menstrual cycle is an endogenous system, evidence suggests that it may be influenced by exogenous factors, such as the cycles of other women.
describe a study that has explored an infradian rhythm.
McClintock & Stern (1998)
Aim: to investigate whether the menstrual cycle is influenced by pheromonal secretions by other women.
Sample: 29 female university students, not taking birth control pills.
Design: quasi-experiment with independent measures.
describe McClintock & Stern (1998) method.
samples of pheromones were gathered from 9 of the women at different stages of their menstrual cycles via a cotton pad placed in their armpit (for at least 8 hours). The other 20 participants were exposed to the pheromones and their menstrual cycles were monitored.
describe McClintock & Stern (1998) results.
when the experimental group inhaled secretions from women who were about to ovulate, their menstrual cycles became shorter.
When they inhaled secretions from women who had just ovulated, their menstrual cycles became longer.
McClintock found that 68% of women experienced changes to their cycle.
describe McClintock & Stern (1998) conclusions.
the experimental groups menstrual cycles were affected by the secretions from the control group.
This explains why when a group of women live in close proximity, their menstrual cycles tend to sync.
what is an evolutionary perspective on McClintock & Stern’s study?
Evolutionary psychologists argue that it may well be that there was once an evolutionary advantage to having all the women in a community menstruate at approximately the same time.
Menstrual synchrony has an evolutionary value. If women fall prgenant around the same time new born babies can be cared for collectively within a social group, which increases chance of survival.
However the validity of this evolutionary perspective has been questioned. Schank 2004 argued that too many women cycling together will increase competition for the best males.
As the competition is high, some of them will miss out.
Therefore it is uncertain whether synchronous menstrual has the evolutionary value that has been claimed.
what are the methodological issues of McClintock & Stern’s study?
A limitation of the early synchronization studies are the methodologies employed.
It is argued that there are many factors that may affect change in a woman’s menstrual cycle, including stress, exercise that might act as confounding variables.
This means that any supposed pattern of synchronization, as seen in the studies by McClintock and others, is no more than would have been expected to occur by chance.
It could therefore be argued that such studies lack interval validity and are not measuring what they are supposed to measure, due to the lack of control.
what evidence is there to support the suggestion that menstruation is governed by exogenous zeitgebers?
A strength of the explanation that the menstrual cycle is, to some extent, governed by exogenous zeitgebers is that there is supportive evidence.
Reinberg (1967) examined a woman who spent three months in a cave with only a small lamp to provide lamp to provide light. Reinberg noted that her cycle shortened from the usual 28 days to 25.7 days.
This result suggests that the lack of light in the cave affected her menstrual cycle.
Therefore this demonstrates the effect of external factors on infradian rhythms.
Give an example of, and describe the clinical presentation of a psychological disorder that has an infradian rhythm.
SAD is a depressive disorder which has a seasonal pattern of onset and is descried and diagnosed as a mental disorder in DSM-5.
As with other forms of depression, the main symptoms of SAD are persistent low mood alongside a general lack of activity and interest in life.
SAD is often referred to as the ‘winter blues’ because the symptoms are triggered during the winter months when the number of daylight hours become shorter.
that biological rhythm does SAD follow?
SAD is a particular type of infradian rhythm called a circannual rhythm as it is subject to a yearly cycle.
what is a potential mechanism for the SAD disorder?
It is believed 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 the secretion process continues for longer.
This is thought to have a knock on effect on the production of serotonin in the brain, the neurotransmitter linked to depression.
what is a common treatment for SAD?
light box therapy.
which study that would cast doubt on the impact of an exogenous zeitgeber on seasonal affective disorder?
One limitation of the explanation that the exogenous zeitgebers of light affects the infradian rhythm of SAD is that there is mixed evidence.
One of the most effective treatments for SAD is phototherapy. This is a lightbox that stimulates very strong light in the morning and evening. It is thought to reset melatonin levels in people with SAD. Eastman et al (1998) found that this relieves symptoms in 60% of sufferers. However, the same study recorded a placebo effect of 30% using a fake generator.
If SAD was solely due to biology, then the fake generator would not have caused a relief in symptoms in the fake generator.
This casts doubt on the chemical influence of phototherapy and suggests that sad may also be influenced by psychological factors.
Outline a limitation of therapy for seasonal affective disorder.
One limitation of SAD therapy is that its effects may be short term.
Sanassi (2014) found that light therapy reduced symptoms of SAD in 80% of people.
However, Rohan et al (2009) recorded a relapse rate of 46% of over successive writers, compared to 27% in a comparison group receiving CBT.
This suggests that light therapy may be an effective short-term treatment but additional treatments may be required if benefits are to be maintained.