Discuss research into circadian rhythms. Refer to evidence in you answer.
(16 marks)
Circadian rhythms are biological cycles lasting 24hours such as the sleep/wake cycle and
core body temperature. The circadian rhythm of the sleep and wake cycle is controlled by
external environmental changes/cues like light (exogenous zeitgebers) the fact why we are
alert during daytime and drowsy at night is because of daylight and by endogenous
pacemakers the body’s internal biological clock.
Siffre investigated the effect of the removal of light (exogenous zeitgeber) on the circadian
rhythm of the sleep and wake cycle. He spent 6 months in a cave without light and sound
and continued to fall asleep and wake up on a regular schedule. His ‘free running’ biological
rhythm settled down to around 25 hours despite getting rid of the external cue light
highlighting circadian rhythms persist despite the removal of light (exogenous zeitgebers.)
His study is supported by Aschoff and Wever who got participants to spend 4 weeks in a
WW2 bunker deprived of light (exogenous zeitgeber). Their study found all participants
displayed a circadian rhythm between 24-25 hours, with one participant whose sleep and
wake cycle was of 29 hours. Both Siffre and Aschoff study found that the sleep/wake cycle
may be a bit longer than 24 hours.
The other example of a circadian rhythm is the core body temperature cycle, which is lowest
at around 4am (36 degrees) and highest at 6pm (38 degrees). The core body temperature
has been linked to mental abilities. Folkard et al found that children who had stories read to
them at 3pm showed superior recall and comprehension after a week compared to children
who heard the same stories at 9am.
A strength of circadian rhythms is practical application to shift work. For example, Boivin et
al found that night workers who engaged in shift work experience a period of reduced
concentration around 6 in the morning meaning mistakes and accident are most likely to
happen. This research is useful to employers as it shows them when productivity is at its
lowest and when incident is more likely at the work place so they could try to avoid them.
Thus, research into the sleep and wake cycle may have economic implication in terms of
how best to manage worker productivity.
Another strength of Siffre study was that it had high level of control. This is as Siffre
controlled the light (exogenous zeitgebers) and this allowed a causal relationship to be
established. However, a limitation is his case studies involved a small sample. For example,
Siffre cave study was a single case study involving only one individual himself therefore
finding can’t be generalised as Siffre is not representative of the wider population.
Moreover, Siffre noticed at the age of 60 his internal clock ran slower than when he was a
young man showing that individuals of different ages have unique circadian rhythms. Thus,
this limits the external validity of the study.
A limitation of Circadian rhythms is individual differences. For example, Duffy et al found
that some people preferred to go to sleep early (larks) whereas some people preferred to
do the opposite. Therefore, this shows people circadian rhythms vary.
(16 marks)
Circadian rhythms are biological cycles lasting 24hours such as the sleep/wake cycle and
core body temperature. The circadian rhythm of the sleep and wake cycle is controlled by
external environmental changes/cues like light (exogenous zeitgebers) the fact why we are
alert during daytime and drowsy at night is because of daylight and by endogenous
pacemakers the body’s internal biological clock.
Siffre investigated the effect of the removal of light (exogenous zeitgeber) on the circadian
rhythm of the sleep and wake cycle. He spent 6 months in a cave without light and sound
and continued to fall asleep and wake up on a regular schedule. His ‘free running’ biological
rhythm settled down to around 25 hours despite getting rid of the external cue light
highlighting circadian rhythms persist despite the removal of light (exogenous zeitgebers.)
His study is supported by Aschoff and Wever who got participants to spend 4 weeks in a
WW2 bunker deprived of light (exogenous zeitgeber). Their study found all participants
displayed a circadian rhythm between 24-25 hours, with one participant whose sleep and
wake cycle was of 29 hours. Both Siffre and Aschoff study found that the sleep/wake cycle
may be a bit longer than 24 hours.
The other example of a circadian rhythm is the core body temperature cycle, which is lowest
at around 4am (36 degrees) and highest at 6pm (38 degrees). The core body temperature
has been linked to mental abilities. Folkard et al found that children who had stories read to
them at 3pm showed superior recall and comprehension after a week compared to children
who heard the same stories at 9am.
A strength of circadian rhythms is practical application to shift work. For example, Boivin et
al found that night workers who engaged in shift work experience a period of reduced
concentration around 6 in the morning meaning mistakes and accident are most likely to
happen. This research is useful to employers as it shows them when productivity is at its
lowest and when incident is more likely at the work place so they could try to avoid them.
Thus, research into the sleep and wake cycle may have economic implication in terms of
how best to manage worker productivity.
Another strength of Siffre study was that it had high level of control. This is as Siffre
controlled the light (exogenous zeitgebers) and this allowed a causal relationship to be
established. However, a limitation is his case studies involved a small sample. For example,
Siffre cave study was a single case study involving only one individual himself therefore
finding can’t be generalised as Siffre is not representative of the wider population.
Moreover, Siffre noticed at the age of 60 his internal clock ran slower than when he was a
young man showing that individuals of different ages have unique circadian rhythms. Thus,
this limits the external validity of the study.
A limitation of Circadian rhythms is individual differences. For example, Duffy et al found
that some people preferred to go to sleep early (larks) whereas some people preferred to
do the opposite. Therefore, this shows people circadian rhythms vary.
