circadian rhythms Flashcards
What is a circadian rhythm?
-Biological Rhythms subject to a 24 hour cycle which regulate multiple body processes
What are examples of circadian rhythms?
-Changes in body temperature, and the sleep/wake cycle
What is the sleep/wake cycle in charge of?
-when humans fall asleep and wake up
What is the sleep/wake cycle influenced by?
-exogenous pacemakers
-exogenous zeitgebers
What is the endogenous pacemaker that influences the sleep/wake cycle?
The SCN (suprachiasmatic nucleus)
What exogenous zeitgebers influence the sleep/wake cycle?
Time, Daylight
What are the studies into the sleep/wake cycle?
Aschoff and Wever, Siffre, Folkard
What was the aim of Siffre’s cave study?
-study the effects when deprived of exposure to natural light and sound on his own biological rhythms
What was the procedure of Siffre’s study?
-Spent several, extended periods underground
-In one study he spent 2 months in the caves of the Southern Alps
-In another study he spent 6 months in a Texan cave.
What were the findings of Siffre’s study?
His own biological rhythm settled to one just beyond the usual 24 hours (settled to 25 hours), and he continued to fall asleep and wake up on a regular schedule.
What were the conclusions of Siffre’s study?
The sleep/wake cycle may be slightly longer than 24 hours but that is entrained by exogenous zeitgebers associated with our 24 hour day.
What was the procedure of Aschoff and Wever’s study?
Convinced a group of participants to spend 4 weeks in a World War Two bunker, deprived of natural light.
What were the findings of Aschoff and Wever’s study?
All but one of the participants displayed a circadian rhythm between 24 and 25 hours.
What were the conclusions of Aschoff and Wever’s study?
The sleep/wake cycle may be slightly longer than 24 hours but that is entrained by exogenous zeitgebers associated with our 24 hour day.
What was the aim of Aschoff and Wever’s study?
-study the effects that lack of natural light can have on a human’s circadian rhythm/ sleep wake cycle
What was the procedure of Folkard’s study?
-Studied a group of 12 people who agreed to live in a dark cave for 3 weeks, retiring to go to bed when the clock said 11:45 pm and rising when it said 7:45 am.
-Over the course of the study, researchers secretly gradually sped up the clock, so that an apparent 24 hour day only lasted 22 hours.
What were the findings of Folkard’s study?
Only 1 participant was able to comfortably adjust to the new regime
What were the conclusions of Folkard’s study?
The existence of a strong free-running circadian rhythm cannot easily be overridden by exogenous zeitgebers.
What was the aim of Folkard’s study?
See if time (an exogenous pace-maker) has that much of an influence of your natural circadian rhythm
What are the strengths of circadian rhythms?
-real-world applications in terms of understanding the consequences if they are interrupted
-real-world applications in terms of making beneficial changes to structures
Explain the strength of circadian rhythms that there are real-world applications (in terms of understanding consequences)?
-Research into circadian rhythms provides an understanding of the consequences when they are disrupted, for example, when doing shift work.
-Night workers experience a period of reduced concentration at around 6am (a circadian trough) meaning that mistakes and accidents are more likely (Bovin et al).
-Research has also pointed to a relationship between shift work and poor health- shift workers are 3x more likely to develop heart disease.
-This shows that research into the sleep wake cycle may have real-world economic implications in terms of how best to manage productivity.
What are the limitations of circadian rhythms?
-it is hard to make generalisations
-methodological issues of research support
Explain the strength of circadian rhythms that there are real-world applications in terms of making beneficial changes to structures?
-Researchers such as Wolfson and Carskadon (1998) recommended that the school day start a couple of hours later to fit in with the typical teenage circadian rhythm.
-Hormonal shifts in the teenage body mean that getting to sleep becomes more difficult and therefore adolescent students tend to be tired at the start of the school day.
-This likely impacts upon their academic performance in the morning and throughout the day if they are sleep-deprived.
-Research has shown benefits for academic and behavioural performance when lessons start later in the day, including reduced caffeine dependence.
-This is a strength because it suggests that valuable changes can be made to how certain things are run to benefit society.
Explain the limitation of circadian rhythms that it is hard to make generalisations?
-This is because the sleep-wake cycle/ people’s circadian rhythms are subject to change from person to person
-Czeisler found individual differences in sleep/wake cycles varying from 13 to 65 hours.
-Duffy et al (2001) found that some people have a natural preference for going to bed early and rising early, categorised as ‘larks’, while others preferred the opposite (‘owls)- this generally varies based on age, with adults more likely to be ‘larks’ and teenagers more likely to be ‘owls’.
-Siffre observed that his own sleep/wake cycle had slowed since he was a young man.
-This means that it is difficult to use research data to discuss anything more than averages, which may be meaningless.
Explain the limitation of circadian rhythms that there are methodological issues of research support?
-participant samples in studies such as Siffre’s and Folkard’s were both very small- Folkard had just 12 participants, while Siffre conducted a case study of just himself.
-This is problematic because sleep/wake cycles vary from person to person, and small groups mean that if an anomalous/ extreme result is shown (for example if someone has a significantly longer or shorter circadian rhythm) results will be skewed.
-Another problem is that any artificial light that participants may have had access to may have been strong enough to stop production of melatonin, altering the participant’s sleep-wake cycle by essentially resettling their circadian rhythms.
-This suggests that findings may not be completely valid/ accurate.
