Circadian Rhythms Flashcards
What is a biological rhythm?
-Cyclical change in the way bio systems behave, repeated periodically and controlled by endogenous pacemakers and/or exogenous zeitgebers
What is a circadian rhythm?
A rhythm lasting approximately 24 hours
What is the sleep/wake cycle
The 24 hour cycle in which we fall asleep and wake up, widely believed to be heavily influenced by external cues such as sunlight/social interaction. However, also internal clock which is free running
What did Michael Siffre do?
- Underground stays on 3 occasions
- Absence of exogenous zeitgebers such as daylight, clocks, radio
What was the only thing influencing Siffres behaviour?
The ‘free running’ internal clock
Siffre’s First Stay…
Alps, 61 days, resurfaced believing it was 20th of August when it was the 17th of September
Siffres Second Stay…
Texan cave for 6 months, rhythm settled to just over 24 hours but could shift to as many as 48
Siffres Third Stay…
To observe the effects of ageing. Found internal clock ticked more slowly compared to when he was younger
What does Siffres research highlight?
The existence of an internal circadian clock that is able to work independently. Importance of exogenous zeitgebers in regulating it tho
Siffre’s findings were supported by Aschoff and Wever…
- WW2 bunkers without any external cues
- Rhythms were found to be 24/25 hours, some as high as 29
What do Aschoff and Wevers WW2 bunker studies show?
Gives further credit to the idea there is an internal bio clock that can persist without the influences of external cues
However, a criticism of research into circadian rhythms is that there is a critical flaw in terms of research methodology..
- Still exposed to external cues (artificial light)
- Lacks validity as does not reflect changes that would occur in complete absence
The importance of this methodological flaw is reinforced by Czeisler…
Rhythms could be manipulated and reduced to 22 ours or increased to 28 hours using dim lighting - role of external cues
Further criticism of circadian rhythm research is that it ignores the role of individual differences…
- Cycles can range from 13 hours to 65 hours
- Morning people prefer to rise early and vice versa
- Siffre had concluded sleep wake cycle was 24 hours?
External validity of Siffres research has been questioned…
- Treated as case study rather than experiment
- Lacks generalisability, how Siffre’s clock reacted does not reflect others
Research into circadian rhythms are typical of the biological approach, thus determinist…
- Study of blind man supportive of bio approach
- His internally set rhythm could not be changed, despite exogenous zeitgebers used to try and influence it
What does the study of a young blind man suggest?
- S/W cycles/C rhythms are biologically ingrained and can work in the absence of external cues
HOWEVER, the human body is far more complex than this deterministic, and therefore reductionist view…
- Human body is far more complex
- Further studies demonstrate that EX cues do play a strong role, to some degree
Core body temperature is a second example of a circadian rhythm within our bodies. Research has shown what?
Lowest at 4.30am - 36 degrees
Highest at 6pm - 38 degrees
Slight trough after lunch which occurs even in the absence of food
What is a positive application of research into core body temperatures?
Knowledge can be used to heighten our cognitive abilities
What was Folkard’s research? (RWA)
- Learning abilities of 12/13 y/os
- Stories read either at 9am or 3pm
- After one week the afternoon group were superior in both research and comprehension (8% more)
What can Folkard’s knowledge be used for?
Can be of great use to people when performing cognitive tasks as they help people become aware of when their potential is at its highest
What is another positive application aside from cognitive abilities?
- Chronotheraputics (how timing affects drug effectiveness)
- Circadian rhythms affect heart rate, hormones, digestion etc
- Drugs targeted at specific hormones can be taken when hormone level is high to work at their optimum
So what has knowledge of circadian rhythms allowed us to do (chronotheraputics)
Increase the effectiveness of medication and ultimately health
