Bio rhythms- Circadian rhythms

Question 1

What are biological rhythms?

Answer 1

Distinct patterns of change in body activity that conform to cyclical time periods

Question 2

What are circadian rhythms?

Answer 2

Biological rhythms that are subject to a 24 hour cycle, regualting bodily processes (e.g: sleep/wake cycle)

Question 3

What are biological rhythms governed by?

Answer 3

• The body’s internal biological clock (endogenous pacemakers)
• External changes in the environment (exogenous zeitgebers)

Question 4

What type of rhythm occurs many times during the day?

Answer 4

Ultradian rhythms

Question 5

What type of rhythm take more than a day to complete?

Answer 5

• Infradian rhythms
• Circannual rhythms (even longer)

Question 6

How long do circadian rhythms last?

Answer 6

Around 24 hours

Question 7

What is the sleep/wake cycle governed by?

Answer 7

• Exogenous zeitgebers (effects of daylight)
• Endogneous pacemakers (suprachiasmatic nucleus- SCN)

Question 8

Where is the SCN and what does it do?

Answer 8

• Lies above the optic chiasm (provides info from eye about light)
• Exogenous zeitgebers reset SCN

Question 9

What did Siffre study?

Answer 9

Studied the effects of spending extended periods underground on his own biological rhythms

Question 10

What was Siffre’s procedure?

Answer 10

• 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

Question 11

What did Siffre find?

Answer 11

• 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

Question 12

What was Aschoff and Wever’s study and findings?

Answer 12

• 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

Question 13

What was Folkard et al study and find?

Answer 13

• 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

Question 14

Strength:
I- Shift work

Answer 14

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

Question 15

Limitation:
I- Shift work studies use correlational methods

Answer 15

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

Question 16

Strength:
I- Improves medical treatment

Answer 16

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

Question 17

Limitation:
I- Indivdiual differences

Answer 17

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 16-65 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

Question 18

Evaluation extra:
I- Shifting the school day

Answer 18

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)

Question 19

Siffre 1962

Answer 19

• 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

Question 20

Aschoff and Wever 1976

Answer 20

• 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)

Question 21

Folkard 1985

Answer 21

• 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

Question 22

Boivin 1966

Answer 22

• Night workers engaged in shift work experience a reduced concentration at 6am

Question 23

Knutsson 2003

Answer 23

• Found a relationship between shift work and poor health
• Shift workers are 3x more likely to develop heart disease

Question 24

Soloman 1993

Answer 24

• High divorce rates in shift workers may be partly due to the strain of deprived sleep

Question 25

Bonten 2015

Answer 25

• 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

Question 26

Czeisler 1999

Answer 26

• Individual differences in the sleep/wake cycle varying from 16-65 hours

Question 27

Duffy 2001

Answer 27

• Some people have a natural preference for going to bed and rising early (larks) vs (owls)

Question 28

Folkard et al 1977

Answer 28

• Children who had stories read to them at 3pm showed superior recall and comprehension after a week vs control who heard stories at 9am

Question 29

Gupta 1991

Answer 29

• Improved performance on IQ tests when participants were assessed at 7pm vs at 2pm and 9am