infradian rhythms Flashcards
infradian rhythm
a type of biological rhythm with less than 1 cycle in 24 hours
2 examples of infradian rhythms
- SAD seasonal affective disorder
- menstruation
what is SAD
circannual rhythm subject to a yearly cycle
- symptoms of low mood and general lack of activity and interest in life
- a form of depression
what is SAD triggered by
the number of daylight hours becoming shorter
- its affected by the exogenous zeitbergs light and darkness
the menstruation cycle
- average length of 28 days
what is menstruation regulated by
- by hormones
- ovulation takes place halfway through the cycle
is menstruation endogenous or exogenous
endogenous as its regulated by hormones
- however it may be influenced by exogenous factors
whats the key study for infradian rhythms
mcclintock and stern
mcclintock and stern aim
To investigate if menstrual cycles (an example of an infradian rhythm) can be influenced by
exogenous zeitgebers such as female pheromones. (Pheromone: a chemical substance produced
and released into the environment by an animal, especially a mammal or an insect, affecting the
behaviour or physiology of others of its species).
mcclintock and stern method
The sample consisted of 29 women with a history of irregular periods. Samples of pheromones
were gathered from 9 women at different stages of their menstrual cycles via a cotton pad placed
in their armpit which they wore for at least 8 hours. The pads were then treated with alcohol and
frozen, to be rubbed on the upper lip of other participants. On day one pads from the start of the
menstrual cycle were applied to all 20 women, on day two they were given the pad from the
second day of the cycle and so on.
mcclintock and stern results
The researchers found that 68% of the women experienced changes to their cycle which brought
them closer to the cycle of their ‘odour donor’
mcclintock and stern conclusion
This suggests that a woman’s menstrual cycle can be altered by communication with pheromones
(exogenous factors).
small sample size
McClintock & Stern only had a small sample of 29 women. This means that the population
validity of this sample is limited.
E As such, their conclusion that a woman’s menstrual cycle can be altered by communication
with pheromones (exogenous factors) may be invalid since their sample may be
unrepresentative of a wider population.
E However, there is no evidence that this is, in fact the case. As such, it is reasonable to argue
that the small sample size alone is not sufficient reason to discount the findings or conclusions
of this research.
correlational data
An issue with McClintock & Stern’s evidence is that it is only correlational.
E This means that they have not proven that a woman’s menstrual cycle can be altered by
communication with pheromones (exogenous factors) as other factors may have been
involved.
E However, there was clear evidence of a correlation between exposure to exogenous factors
and an alteration in the menstrual cycle – although this evidence is limited by the fact that this
correlational was not universal (see below).
practical application
One of the most effective treatments for SAD is phototherapy.
E This is a lightbox which stimulates very strong light in the morning and evening. It is thought to
reset melatonin levels in people with SAD and relieves symptoms in up to 60% of sufferers
(Eastman et.al. 1998).
E Although there remains some debate in relation to phototherapy, its apparent success suggests
that infradian rhythms are indeed affected by exogenous zeitgebers such as light.
methodological issues
There are many factors which may affect women’s menstrual cycles including stress, diet and
exercise.
E These might act as confounding variables which means that the pattern of synchronisation
observed by McClintock & Stern may be no more than would be expected to occur by chance.
E This means that their conclusion that a woman’s menstrual cycle can be altered by
communication with pheromones (exogenous factors) may be invalid.
