biological rhythms: circadian rhythms

Question 1

what is a biological rhythm?

Answer 1

distinct patterns of changes in body activity that conform to cyclical time periods

Question 2

what are biological rhythms influenced by?

Answer 2

• endogenous pacemakers - body’s internal biological ‘clocks’
• exogenous zeitgebers - external changes in the environment

Question 3

what are circadian rhythms?

Answer 3

rhythms that last for around 24 hours

Question 4

what are 2 examples of circadian rhythms?

Answer 4

• sleep / wake cycle
• changes in core body temperature

Question 5

how do exogenous zeitgebers affect the sleep/wake cycle?

Answer 5

feeling drowsy at night and alert during the day demonstrates the effect of daylight on our sleep/wake cycle

Question 6

how do endogenous pacemakers affect the sleep/wake cycle?

Answer 6

• suprachiasmatic nucleus (SCN) lies just above optic chism
• provides information from the eye about light
• exogenous zeitgebers (light) can reset the SCN

Question 7

process of siffre’s cave study (1962)

Answer 7

• siffre has spent several extended periods underground to study the effects on his own biological rhythms
• deprived of exposure to natural light and sound, but with access to adequate food and drink
• spent 2 months in the caves of the southern alps, but only believed it to have been a month
• a decade later, he spent 6 months in a texan cave

Question 8

what are the results of siffre’s cave study?

Answer 8

• his ‘free-running’ biological rhythm settled down to one that was around 25 hours
• continued to fall asleep and wake up on a regular schedule

Question 9

aschoff and wever (1976): procedure

Answer 9

convinced a group of participants to spend 4 weeks in a WW2 bunker deprived of natural light

Question 10

aschoff and wever (1976): results

Answer 10

all but one of the participants (whose sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24-25 hours

Question 11

what do siffre’s experience and the bunker study suggest?

Answer 11

• the ‘natural’ sleep/wake cycle may be slightly longer than 24 hours
• entrained by exogenous zeitgebers associated with our 24h day eg. number of daylight hours, typical mealtimes

Question 12

folkard et al. (1985)

Answer 12

• 12 people who agreed to live in a dark cave for 3 weeks, going to bed when the clock said 11:45pm and rising when it said 7:45am
• over the course of the study, the researchers gradually sped up the clock so an apparent 24h day only lasted 22h
• only 1 was able to comfortably adjust to the new regime

Question 13

what does folkard et al.’s research suggest?

Answer 13

• existence of a strong free-running circadian rhythm cannot easily be overriden by exogenous zeitgebers
• we should not overestimate the influence of exogenous zeitgebers on our internal biological clock

Question 14

core body temperature variations

Answer 14

• varies by around 2°C during the day
• lowest at 4 in the morning (36°C)
• peaks around 6 in the evening (38°C)
• evidence suggests that body temperature may have an effect on our mental abilities; the warmer we are internally, the better our cognitive performance

Question 15

core body temperature: folkard et al. (1977)

Answer 15

demonstrated how children who had stories read to them at 3pm showed superior recall and comprehension after a week compared to children who heard the same stories at 9am

Question 16

core body temperature: gupta (1991)

Answer 16

found improved performance on IQ tests when participants were assessed at 7pm as oppsoed to 2pm and 9am

Question 17

evaluation: provides an understanding of the adverse consequences that occur when circadian rhythms are distrupted (desynchronisation)

Answer 17

• night workers engaged in shift work experience a period of reduced concentration around 6 in the morning (circadian trough) meaning mistakes and accidents are more likely (bolvin et al. 1996)
• shift workers are 3 times more likely to develop heart disease than people who work more typical work patterns (knutsson 2003)
• research into the sleep/wake cycle may have real-world economic implications in terms of how best to manage worker productivity

Question 18

evaluation: studies investigating the effects of shift work tend to use correlational methods (counterpoint)

Answer 18

• difficult to establish whether desynchronisation fo sleep/wake cycle is actually a cause of negative effects
• solomon (1993) concluded that high divorce rates in shift workers might be due to the strain of deprived sleep and other influences such as missing out on important family events
• this suggests that it may not be biological factors that create the adverse consequences associated with shift work

Question 19

evaluation: improvement of medical treatments

Answer 19

• circadiam rhythms co-ordinate a number of the body’s basic processes such as heart rate, digestion and hormone levels, which rise and fall during the day
• this has led to the field of chronotherapeutics: how medical treatment can be administered in a way that corresponds to a person’s biological rhythm
• eg. aspirin as a treatment for heart attacks is most effective if taken last thing at night as research shows that heart attacks are most likely to occur early in the morning (bontent et al. 2015)
• therefore, circadian rhythm research can help increase the effectiveness of drug treatments

Question 20

evaluation: generalisations are difficult to make

Answer 20

• aschoff and wever, and siffre’s research is based on very small samples of participants
• it seems that sleep/wake cycles may vary widely from person to person
• czeisler et al. (1999) found individual differences in SWCs varying from 13-65h
• duffy et al. (2001) found that some people have a natural preference for doing to bed early and rising early (‘larks’) whereas others prefer the opposite (‘owls’)
• siffre (1999) observed that his own sleep/wake cycle had slowed down since he was a young man
• this means that it is difficult to use the research data to discuss anything more than averages, which may be meaningless

Question 21

evaluation: shifting the school day (for)

Answer 21

• wolfson and carskadon (1998) recommend that the school day start a couple of hours later to fit in which the typical teenage chronotype (sleep pattern)
• hormonal shifts in the teenage body mean that getting to sleep becomes more difficult so adolescent students tend to be sleepy at the start of the day
• research has shown benefits for academic and behavioural performance when lessons start later in the day, including reduced dependence of caffeine (adolescent sleep working group 2014)

Question 22

evaluation: shifting the school day (against)

Answer 22

• disruptive for parents and teachers
• limits the number of extracurricular activities after school
• a later school day would not actually reduce sleep deprivation; teenagers would stay up later and still be exhausted