Bio rhythms- Circadian rhythms Flashcards
What are biological rhythms?
Distinct patterns of change in body activity that conform to cyclical time periods
What are circadian rhythms?
Biological rhythms that are subject to a 24 hour cycle, regualting bodily processes (e.g: sleep/wake cycle)
What are biological rhythms governed by?
- The body’s internal biological clock (endogenous pacemakers)
- External changes in the environment (exogenous zeitgebers)
What type of rhythm occurs many times during the day?
Ultradian rhythms
What type of rhythm take more than a day to complete?
- Infradian rhythms
- Circannual rhythms (even longer)
How long do circadian rhythms last?
Around 24 hours
What is the sleep/wake cycle governed by?
- Exogenous zeitgebers (effects of daylight)
- Endogneous pacemakers (suprachiasmatic nucleus- SCN)
Where is the SCN and what does it do?
- Lies above the optic chiasm (provides info from eye about light)
- Exogenous zeitgebers reset SCN
What did Siffre study?
Studied the effects of spending extended periods underground on his own biological rhythms
What was Siffre’s procedure?
- Deprived of exposure to natural sound and light, but had access to food and drink
- Resurfaced in mid-September 1962 after 2 months in the cave
- Repeated this for 6 months in a Texan cave 10 years later
What did Siffre find?
- His free-running biological rhythm settled down to one just beyond the usual 24 hours (25 hours)
- He continued to fall asleep and wake on a regular schedule
What was Aschoff and Wever’s study and findings?
- Participants spent 4 weeks in a WW2 bunker, deprived of natural light
- All but one (29 hours) displayed a circadian cycle of 24/25 hours
- Suggests natural sleep/wake cycle may be longer than 24 hours but is entrained by exogenous zeitgebers associated with the 24 hour day
What was Folkard et al study and find?
- Study of 12 people who lived in a dark cave for 3 weeks (went to bed when the clock said 11:45pm and woke when it said 7:45am)
- Gradual speed up of the clock so the day only lasted 22 hours
- Only one adjusted to this regime
- Suggests the existence of a strong free-running circadian rhythm that cannot be easily overridden by exogenous zeitgebers
Strength:
I- Shift work
D- Provides an understanding of the consequences of disruption to circadian rhythms (desynchronisation). For example, Boivin- night workers enagged in shift work experience a period of reduced concentration at 6am, so mistakes are more likely. Knutsson- research points to a relationship between shift work and poor health. Shift workers are 3X more likely to develop heart disease
E- Shows research into the sleep/ wake cycle may have real world economic implications in terms of how to manage worker productivity
Limitation:
I- Shift work studies use correlational methods
D- This means it’s difficult to establish whether desynchronisation of the sleep/ wake cycle is a cause of negative effects. Soloman concluded high divorce rates in shift workers may be partly due to the strain of deprived sleep
E- Suggests it may not be biological factors creating adverse consequences associated with shift work
Strength:
I- Improves medical treatment
D- Circadian rhythms co-ordinate many of the body’s basic processes (heart rate, digestion, hormone levels). This rise and fall during the day has led to the field of chronotherapeutics (treatment administered in a way that corresponds to a person’s bio rhythms). For example, aspirin is most effective when taken at night, as it reduced blood platelet activity, reducing heart attack risk (Bonten et al)
E- Shows circadian rhythms help increase effectiveness of drug treatments
Limitation:
I- Indivdiual differences
D- Studies are based on very small samples. Sleep/wake cycles may vary between people. Czeisler et al found individual differences in sleep/wake cycles varying from 13-65 hours. Duffy et al found that some people have a natural preference for going to bed and rising early (larks) vs the opposite (owls)
E- Means it’s difficult to use research data to discuss anything more than averages, so data many be meaningless
Evaluation extra:
I- Shifting the school day
Strength: Wolfson and Carskadon recommend the school day start a couple hours later to fit with the typical teenage chronotype (sleep pattern). Research shows academic and behavioural performances is better when lessons start later
Limitation: This would be disruptive for parents/teachers- limits number of extra-curriculars after school. Doesn’t fit with work patterns (9 to 5)
Siffre 1962
- Deprived of natural light in a cave for 2 months
- Found his free-running biological rhythm was 25 hours
- Supports idea that circadian rhythms are approx 24 hours, but this may extend to slightly higher
Aschoff and Wever 1976
- Participants spent 4 weeks in a WW2 bunker
- Found all but one (29 hours) displayed a circadian rhythm of 24/25 hours
- Suggests the natural sleep/wake cycle may be longer than 24 hours but is entrained by exogenous zeitgebers (e.g: light)
Folkard 1985
- 12 participants lived in a cave for 3 weeks
- Clock gradually sped up so the day only lasted 22 hours
- Found only one adjusted to a 22 hour day
- Suggests the free-running circadian rhythm cannot be overridden by exogenous zeitgebers
Boivin 1966
- Night workers engaged in shift work experience a reduced concentration at 6am
Knutsson 2003
- Found a relationship between shift work and poor health
- Shift workers are 3x more likely to develop heart disease
Soloman 1993
- High divorce rates in shift workers may be partly due to the strain of deprived sleep
Bonten 2015
- Found aspirin is most effective when taken at night, as blood platelet activity is reduced. Reduced risk of heart attack as they are most likely to occur in the morning
Czeisler 1999
- Individual differences in the sleep/wake cycle varying from 13-65 hours
Duffy 2001
- Some people have a natural preference for going to bed and rising early (larks) vs (owls)
Folkard et al 1977
- Children who had stories read to them at 3pm showed superior recall and comprehension after a week vs control who heard stories at 9am
Gupta 1991
- Improved performance on IQ tests when participants were assessed at 7pm vs at 2pm and 9am
