A01
The Sleep-Wake Cycle
External cues from the environment
(exogenous zeitgebers) are
important in guiding the circadian
sleep-wake cycle. These include
changes in daylight (you feel sleepy
when it’s dark and are roused by the
sunlight in the morning) or knowing
what time of day it is and therefore
whether it is time to asleep or
awake.
However, there is also an internal
(endogenous) ‘clock’. This internal
circadian clock is ‘free running’
(works without external cues)
setting a cycle of about 24-25 hours.
Under normal circumstances the
internal clock does not work alone.
Studies show that circadian rhythms
persist despite isolation from
natural light, which demonstrates
the existence of an endogenous
‘clock’. However, external cues are
also important; the clock was not
perfectly accurate: it varied from
day to day.
A01: Core Body Temperature
Another circadian rhythm is the core
body temperature cycle. This is one
of the best indicators of the
circadian rhythm. It is at its lowest
at about 4.30am (about 36°C) and
highest around 6pm (38°C).
There is a slight trough just after
lunch which is not just due to the
effects of having lunch- the dip
occurs even when people have not
eaten suggesting that the rhythm is
influenced by the body’s internal
clock.
PSYA3 SLEEP: Learning Table 1 Circadian Rhythms
Circadian Rhythms are those rhythms are those rhythms that last about 24 hours. Two known circadian rhythms are the sleep wake cycle and the body temperature cycle.
A02
Endogenous clock (Internal) evidence and commentary
Exogenous Zeitgebers (External) evidence and commentary
MAID
:-/ Mixed support for a free-running rhythm
 Support for external cues
 Deterministic Vs Free Will
P- There is mixed evidence to support the idea of ‘free-running’ circadian rhythms.
P- However, there is research to suggest that external cues are important
P: An issue with the explanation offered for circadian
E- For example, Siffre (1975) spent six months in a Texan cave with no external cues to guide
in circadian rhythms to an extent because the internal ‘clock’ is not
rhythms is that it is deterministic.
his rhythms – no daylight, no clocks or radio. He slept, woke and ate when he felt like it and
perfectly accurate.
E: This is because they suggest that sleep-wake patterns
found that his natural circadian rhythm settled down to just over 24 hours initially; but
E- For example, Folkard et al. (1985) conducted an experiment to see if
are fixed and pre-determined by internal mechanisms.
changed dramatically to as much as 48 hours.
external cues could be used to override the internal clock. 12 pps lived in
Miles et al (1977) illustrate the power of these internal
E- This provides mixed support because although it suggests that his endogenous pacemakers
a cave for 3 weeks isolated time cues. The volunteers agreed to go to bed
biological clocks using a case of a young man who was
(SCN, pineal gland and the role of melatonin) have internally managed Siffre’s rhythms to 24
when the clock indicated 11.45pm and get up at 7.45am. Initially the clock
blind, which meant that light did not reset his circadian
hours initially, it does suggest that the role of exogeous zeitgebers have an impact on his
ran normally but gradually they quickened the clock until it was indicating
rhythm. He was exposed to various external cues, such
sleep-wake cycle also (e.g. light, social cues). This is because Siffre’s circadian rhythm changed
the passing of 24 hours when only 22 hours had passed. They found that
as clocks, yet found these had little effect on his
to 48 hours and if it was purely down to the role of ‘free running’ circadian rhythms, his sleepat the beginning, the Pps circadian cycle matched the clock but as it
internally set circadian rhythms suggesting that the role
wake cycle would be expected to stay at 24 hours.
quickened their rhythm ceased to match the 22 hour cycle imposed by
of endogenous pacemakers were innate and
L- Consequently, this provides credible support for a free-running circadian rhythm to an
the experimenters (except for one participant who did adapt to the 22
determined his circadian rhythm. However, this
extent. However, most circadian rhythms work with the influences of exogenous zeitgebers
hour cycle).
determinist interpretation maybe misleading. It is clear
additionally, suggesting support for both the roles of endogenous pacemakers (internal
E: This suggests that the circadian rhythm can only be guided to a limited
that the internal mechanism is very powerful but there is
biological ‘clocks’) and exogenous zeitgebers (external time-givers).
extent by external cues because you would expect all Pps to adapt their
some flexibility in the system.
cycles to 22 hours. The fact they didn’t suggests they are a limited
E: For example, this explanation does not take into
 Support for a free-running rhythm
influence in this case.
account ‘choice’ and the individuals ‘free will’ they have
P: Furthermore, there is other empirical evidence to support the idea of a ‘free-running’
L- Nevertheless, this provides some credibility to the idea that external
over their circadian rhythms. We can decide to go to bed
rhythm.
cues are important in circadian rhythms. However, a combination of both
2 hours later than normal and wake up at the same time
E: For example, Aschoff & Wever (1976) placed participants in an underground WWII bunker
exogenous zeitgebers and endogenous pacemakers are evident in
the next day without much difficulty. Folkard et al (1985)
in the absence of any environmental and social time cues. They found that most participants
circadian rhythms such as the sleep wake cycle.
found that one person managed to keep to a 22 hour
displayed circadian rhythms between 24 and 25 hours, yet some were 29 hours.
rhythm with the use of external cues, showing that other
E: This supports the idea that the cycle operates in the absence of external cues and that the
 Further support for external cues
factors can override the internal clock.
natural free-running cycle is about 24 -25 hours
P: However, further evidence for the support of exogenous zeitgebers is
L: Therefore, the explanatory power of endogenous
L: Providing credible support for the role of endogenous pacemakers and the idea of an
provided after Folkard et al’s experiments finished.
pacemakers in the role of circadian rhythms in the
internal biological clock and a ‘free-running’ rhythm.
E: This is because as soon as they were over, the Pps took only a few days
sleep-wake cycle is reduced because there is evidence
to resynchronize their cycles to the available external time cues e.g. clocks
 MI: Lacks Internal Validity
to suggest they can’t exist without the influences of
and daylight.
P: One issue with Aschoff & Wever’s (1976) study is that it is arguably low in internal validity.
exogenous zeitgebers. The fact that individuals have
E: This suggests that the biological clock was ‘re-set’ in the process known
E: This is because they placed all of their participants together in an underground bunker
free will over external cues that also influence our
as entrainment, in particular, light which can reset the body’s main
where they were likely to influence one another. For example, they may have socialized
circadian rhythms, make the role of endogenous
pacemaker, the SCN.
together, eaten together and therefore decide to go to bed and sleep at the same time as one
pacemakers an inadequate explanation overall.
L:
Consequently,
this
suggests
that
the
influence
of
external
cues
are
another.
** Other potential MAID: Biological Approach and link
prominent
in
circadian
rhythms
such
as
the
sleep
wake
cycle
E: This is an issue because it means that external factors may have influenced their circadian
to Science debate –empirical evidence that can be
rhythms and sleep-wake cycle rather than just their internal biological clocks.
falsified, strengthening the debate that Psychology is a
L: Therefore the support that Aschoff & Wever’s (1976) study gives to the idea of a ‘freeScience **
running’ endogenous pacemaker is reduced because their study can be flawed.
Supporting A02 Evidence and Commentary
 Support for core body temperature and cognitive abilities
P: There is empirical evidence to suggest that the circadian variation in the core body
temperature has been linked to cognitive abilities.
E- For example, Folkard et al. (1977) looked at the learning ability of 12 and 13 year old
children who had stories read to them at either 9am or 3pm. They found that after one week,
the 3pm group (higher core body temperature) showed both superior recall and
comprehension, retaining about 8% more material than the morning 9am group.
E: Additionally, Gupta (1991) found that performance on IQ tests was best at 7pm compared
with 9am or 2pm.
E- This suggests that long-term recall is best when body temperature is highest.
L: Consequently, these findings could be used in real-life applications in schools. This increases
the applicability of the research behind the circadian rhythm of core body temperature which
in turn strengthens its explanatory power.
Contradictory A02 Evidence and Commentary
 Evidence to dispute the link between core body temperature and
cognitive abilities
P: However, there is evidence to dispute Folkard (1977) and Gupta (1991)
findings that there is a link between core body temperature changes and
changes in cognitive performance.
E- For example, Hord & Thompson (1983) tested cognitive performance in
a field instead of a lab environment and didn’t find any correlation
E- Wright et al (2002) suggests this may be because higher core body
temperature leads to increased physiological arousal (being anxious in a
lab) and this leads to cognitive performance instead.
L: Consequently, the validity of Folkard (1977) and Gupta (1991) findings
are questioned because arguably they are not purely measuring core
body temperature and cognitive abilities. In turn, the credibility of the link
between core body temperature and cognitive abilities are reduced
because the studies used to support it can be falsified.
A02 MAID for Hormones
MAID
Other methodological Issues can be brought in if
needed e.g:
* Correlation
* Temporal Validity
* ‘Operationalisation’ of Cognitive abilities e.g. Gupta
used IQ tests but Folkard may have used other methods
which may affect Internal Validity of studies which would
then reduce the support and credibility of the link
between Core Body Temperature and cognitive abilities
NB Just make sure you link it back to what it means for
core body temperature etc.
A01: Hormones
Hormone production follows a circadian rhythm.
 Real life applications
Cortisol is at its lowest around midnight and peaks at 6am. It is
P: A strength of the research into circadian rhythms is that it has been used for real life applications.
a hormone related to making us alert when we wake up and
E- For example, chronotherapeutics is the study of how timing affects drug treatments. The circadian rhythm affects digestion, heart rate and hormone secretions which should be taken into account when
can explain why if we awaken at 4am it is hard to think clearly
taking drugs.
(cortisol levels are not sufficiently high for alertness).
E- This is because drugs need to be taken at certain times when they will be most effective, for example, taking asprin. As most heart attacks occur early in the mornings, asprin needs to be taken around
Melatonin (which induces sleepiness) and growth hormone are
11pm which allows it to peak into the blood stream (in 2 – 4 hours). Therefore the importance of research into circadian rhythms such as hormone production is crucial.
two other hormones that have a clear circadian rhythm both
L- Consequently, as the applicability of such research is so prominent in real life, the credibility of research into hormone production is strengthened.
peaking at around midnight.
Potential Exam Questions
1a) Describe research on circadian rhythms (8 marks) (A01 ONLY – write about the sleep wake cycle, core body temperature and hormones. Give in depth and accurate detail to reach the top band)
1b) Evaluate research on circadian rhythms (16 marks) (A02 ONLY – write about EVALUATION points only – mixed support for free running rhythms, cognitive abilities etc. NO A01 WHATSOEVER) MAKE SURE YOU BRING IN MAID).
You have 30 minutes for the sleep section in your exam. Use your time wisely. There are more marks available for A02 points. If you have a 24 mark essay (8 + 16), use 10 mins for A01 and 20 mins for A02. If you have shorter questions, adapt your timing as necessary.
You MUST include DETAIL in ALL OF YOUR ANSWERS (A01 & A02). Make sure you include a mixture of OUTCOME studies AND MAID PEELS in your A02. Aim for 4-5 FULLY ELABORATED DETAILED PEELS that are LINKED to the QUESTION.
Use the WORDS in the Question to structure your answer and USE THEM in your POINTS (P) and LINKS (L).