Discuss Research into Biological Rhythms

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Lauren-Jodie Tash
Discuss research into Biological
Rhythms (24 marks)
A biological rhythm is an innate biologically driven behaviour which is repeated periodically. There is
ample research which has been carried out on biological rhythms, for example Folkard (1985). This
particular research was into circadian rhythm, a biological process which occurs every 24 hours for
example; the sleep/wake cycle and body temperature. Such rhythms are affected by external cues
such as light and sound which are called Exogenous Zeitgebers, they are also affected by internal
cues called Endogenous Pacemakers. Folkard (1985) placed 12 participants into a cave for two
weeks where there was no natural light. They arranged a routine where the participants would both
sleep and wake up at the same time. However, their clocks were changed so each day was a 22 hour
cycle. It was found that all but one participant kept their original cycle of 24 hours. These results show
the existence of Endogenous Pacemakers because the participants kept the same body clock
despite the elimination of the main Exogenous Zeitgeber, light. This is a very strong study in terms of
Endogenous Pacemakers as it shows that they do in fact exist and that they do have an effect on our
Circadian Rhythms. Furthermore, this study is interactionist as it takes into an account both nature and
nurture and shows the interaction between nurture (Exogenous Zietgebers ­ light) and narture
(Exogenous Pacemakers). However, there are strong criticisms for this study due to the fact that this
experiment only used 12 participants which is a tiny minority. This means that this particular
experiment severely lacks population validity due to the sample being so small and the results may
not be able to be generalised. It could also be argued that this particular study is extremely unethical
due to the fact that participants were kept in a cave for two weeks without any natural sunlight which
would mean that the participants would be extremely deprived in Vitamin D which could affect the
health of all of the participants.
The findings of this piece of research is in fact supported by another piece of research carried out my
Siffre (1972) who remained in a cave for 6 months without any natural light, clocks or any other
indication that told him what time it was. Although this was the case, it was found that he had an
erratic sleep pattern which, when exposed back to natural light, settles down to a 25 hour cycle
instead of the 24 hour cycle which has been suggested we have. This therefore shows that the sleep
wake cycle does continue despite the absence of the main Exogenous Zeitgeber, light and that the
exposure to light `resets' our biological clock back to normal. This piece of research also has the same
criticism's as Folkard (1985) however, a further criticism for this study is the fact that it is a case study
that lacks ecological validity so cannot be used to generalise its results. However, this research has
been criticised by Czeisler for having methodological issues as he argues that artificial light can
`reset' our biological clock, which is what Siffre was exposed to. Czeisler carried out his own study
where ppts were only exposed to artificial low light and made the cycle 28 hours in order to make
the study more valid. He found that by monitoring the participant's temperature and body chemistry
the body clock is in fact 24 hours, not 25 as both Siffre (1972) and Folkard (1985) suggested. This
piece of research argues the fact that there are extraneous variables, like light and temperature that
do affect our sleep-wake cycle no matter what form of light it is.
As well as research into Circadian Rhythms, there has also been research into infradian Rhythms. An
Infradian rhythm is a rhythm that lasts more than 24 hours, for example, the menstrual cycle. It has

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Lauren-Jodie Tash
been researched that the pheromone hormones, can affect a woman's menstrual cycle and cause
them to synchronise with one another. Such research has been carried out by Russel (1980) who took
the pheromones from one woman through cotton wool on her armpit, rinsed it to remove the
bacteria and placed the pheromones on the top lip of a small group of participants in the
experimental group. The same was done with participants in a control group without the hormones.…read more


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