Micheal Siffre's study
Aim: To see if our sleep wake cycle is regulated by an internal clock (endogenous pacemaker). Method: He lived in caves for long periods of time, where he had no external cues or exogenous zeitgeber. He measured at what times he woke up and went to sleep. He only had a head lamp as light. Findings: His rhythm settled to 25 hours on average. Just over 24 hours: Conclusion: The sleep wake cycle is a circadian rhythm and it is free running, regulated only by the endogenous pacemaker
+ves Good control of extraneous varibles, caves stay at a constant temperature, and there is no natural light.
+ve His research is supported by others such as Aschoff and Wever.
-ves Artificial light has since been shown to be an exogenous zeitgeber
-ves Caves are colder than most other places... So research is not generalisable and therfore low external validity.
-ves It was also a case study so results don't represent the population so again low external validity
Aschoff and Wever
Aim: to investigate whether the sleep wake cycle is a circadian rhythm
Mehod: placed PPs in an underground WWII bunker.
Findings: the sleep wake cycle settled to between 24 and 14 hours, although some were as long as 29 hours
Conc: sleepwake cycle is regulated by endogenous pacemaker
+ves, good control of variables - high internal validity
+ves supported by siffre, so reliable
-ves he used students, so not representative of population so low external validity
-ves had artificial light which is an exogenous zeitgeber, which resets sleep wake cycle
Aim : to investigate the role of exogenous zeitgebers on our endogenous pacemaker, and whether they can overide our endogenous pacemaker.
Method: a group of 12 people agreed to live in a cave for 3 weeks. They agreed to go to sleep at 11:45pm and wake up at 7:45am. The clock gradually got faster top run at 22hour cycles.
Findings: As the clock quickened, the pps sleep wake cycle continued at a 24 hour pace, rather that the 22hour one, with the expection of 1 pp.
Conclusion: Suggests that circadian rhythms can only be guided to a limited extent by external cues.
+ves high contol no natural light, and constant temp.
-ves low external validity as it was a small sample, and cabes have a lower base temperature, and therfore results cannot be generalised to the general population
-ves individual diff, some people would not be able to fall asleep specifically at 11.45pm
Cziesler et al 99
Aim: to investigate the effect of artificial light on endogenous pacemakers
Findings: he could alter pps circadian rhythms down to 22hours and up to 28hours, just using dim lighting.
Conclusion: artificial light is a confounding variable in earlier research
He also found out circadian rhythms can vary from 13 to 65 hours
Duffy et al 2000
Aim to investigate the effect of individual differences on circadian rhythms
Findings: morning people prefer to rise early and go to bed early, whereas evening people prefer to wake and go to bed later.
Folkard et al 1977
Aim to investigate the link between circadian variation in core body temperature and cognitive abilities
Method: looked at the learning ability of 12-13year olds, they had to read stories at either 9am or 3 pm.
Findings: After 1 week the group that read at 3pm (higher temp-higher body temp) had greater recall and comprehension, retaining 8% more meaningful material.
Conclusion: Long term recall is best when body temp is highest
Evaluation +ves measured two types of cognitive ability, +ves showed how core body temp can effect circadian rhythms +supported by other resesarch
-ves did not manipulate CORE body temp, -ve cause and effect??
Aim to investigate the effect of core body temperature on cognitive ability.
Ibuka and Kawamura 1975
Aim: to investigate the location of the endogenous pacemaker
Method: looked into individuals with lesions of the supra-chiasmatic nucleus
Findings: they had disrupted circadian rhythms
Conclusion: SCN is the basis of our endogenous pacemaker.
Rusack and groos 82
There is a correlation between cyclical changes in behaviour and the activity of neurons in that area of the brain (SCN)
Hard and Ralph 1998
Aim: to investigate whether the SCN is our endogenous pacemaker
Method: grafted SCNs of hamster with a 22hour circadian rhythm on to hamsters who had a different (24hour?) rhythm
Findings: The hamsters adapted to the new circadian rhythm. ( Their sleep wake cycle now ran on a 22 hour basis)
Conclusion: SCN is our endogenous pacemaker
+ve supported by other studies, high external reliability
-ve done on animals, so not generalisable, low external validity
Aim: to investigate the effect of light on biological rhythms
Method: Sent a young women to go and live in a cave for 3 months, with no external source of light.
Findings: The womens day lengthened to 24.6hours, and her menstraul cycle was shortened to 25.7 days.
Conclusion: the lack of light as a zeitgeber resulted in changes to her circadian and infradian rhythms.
Gold et al 1992
Aim: to investigate the effect of a disrupted circadian rhythm as a result of shift work
Method: conducted a hospital based survey
Findings: Nurses who worked rotating shifts were twice as likely to fall asleep while driving to work and were twice as likeley to report an accident due to sleepiness. Compared to those who only worked day or evening shifts.
Aim: to investigate the long term effects of shift work
Findings: difficulties in social and family relationships, development of peptic ulcers, chronic fatigue, depression, cardiovascualr issues, pregnancy issues. The severity dpends in individual factors. 20% of all worker have to leave shift work due to serious health consequences.
Conc: There can be serious long term effects from shift work.
Aim: to investigate possible improvements in health and productivity through changing the patterns of shift work.
Method: S/he studied workers in a chemical company in Utah. The company operated a three-shift system, in which emplloyees worked a day shift for a week, then a nigh shift and then an evening shift, before starting the cycle again. The effects of the lengthening period between shift changes and rotating shifts in opposite directions (clockwise) in line with the body's preference for longer rather that a shorter day were assesed.
Resullts: both the productivity and health of the workers improved.
Conclusion: It is possible to modify the effects of shift work.
Williamson and Sanderson 86
They found that bringing in a more rapidly rotating system, where workers never worked for more than three nights consequtivley led to health improvements
Pisarki et al 08
'Negative consequences of shift work can be redued if they felt they had sufficient social work and controll at work'
Stress= impaired immune system functioning
Touitou and Bogdan 07
The use of the hormone Melatonin can be used effectivley in adjusting biological rhythms.
Cho et al 2000
Aim: to investigate the effect of jet lag on the disruption of circadian rhythms.
Method: assesed members of cabin crew for cognitive abililty
Findings: Cabin crew had issues with their working memory, which became apparent after several years of ciradian rhythm disruption.
Aim: to investigate the long term effects of frequent jet lag
Method: Participants were healthy 20 healthy women who had worked for at least 5 years as flght attendants. PPs were who were only allowed a few days rest between flights were compared to those who were allowed longer recovery periods.
Findings: Those who had short recovery time performedwprse on memory tests, they showed slower reaction times, and made more mistakes. Brain scans showed they had significant shrinkage of the right temporal lobe, this was correlated with high levels of cortisol (stress hormone).
Conclusion: repeated jet lag, with insuffiecient recovery time between flights can lead to reduced cognitive ability and brain damage.
Herxheimer and Petrie 2002
Melatonin can be effective in treating the immediate effects of jet lag, if taken at the right time.
Demet and Kleitman 1957
Found that REM sleep shows a distinct pattern of brain activity and that it is predmoninantly associated with dreaming
Found that 90% woken in REM reported dreaming, compared with only 7% of those woken in NREM
Found that removing the scn cells from hamsters made circadian rhythms disappear, but that they returned when cells were transplanted in.
This shows the SCN's role as our endogenous pacemaker.
Klein et al 1993
Found that a blind man with a circadian rhythm of 24.5hours got out of his sync with the 24 hour day cycle. He took medication to regulate his sleep wake cycle. Suggesting light acts as an exogenous time cue
Klein et al 1972
Aim to investigate the effect of jet lag in relation to phase advance and phase delay
Findings: Adjustment to jet lag occured more easily on westbound flights, whether outbound or homebound.
Conclusion: it implies that phase advance has more severe consequences than phase delay.
Cziesler et al 1982
Aim: to investigate the effect of shift work on health
Findings shift workers had high illness rates sleep disorders and elevated stress levels.
Conclusion: This suggests that internal body clocks were out of sync with exogenous zeitgebers. Moving to a phase delay system of rotating shifts in forward in time reduced negative effects
Found that melatonin reduced the time required to adjust to shift-work patterns and rotations