Biological rhythms

Question 1

How long do circadian rhythms last for?

Answer 1

24 hours

Question 2

Give an example of a circadian rhythm.

Answer 2

The sleep/wake cycle.

Question 3

What are the exogenous zeitgebers which may affect the sleep/wake cycle?

Answer 3

Light
Phone use

Question 4

What is the endogenous pacemaker involved in the sleep/wake cycle?

Answer 4

The biological clock ‘SCN’.

Question 5

What did Siffre do in his case study?

Answer 5

Siffre spent several extended periods underground to study the effects of his own biological rhythms.
This shows what happens with the deprival of exogenous zeitgebers of adequate food and drink.

He spent two months in the cave and afterwards, he spent 6 months again.

In each case, his biological rhythm settled down to one that was 25 hours.

This shows what happens with the deprival of exogenous zeitgebers such as daylight and sound but also shows the influence of endogenous pacemakers as his biological rhythm did not reach extremes.

Question 6

What did Aschoff and Wever’s research into sleep/wake cycles find?

Answer 6

They convinced a group of participants to spend four weeks in a WW2 bunker deprived of natural light.

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

Both Siffre’s study and this study show that the ‘natural’ sleep-wake cycle can be slight longer than 24 hours but it is entrained by exogenous zeitgebers.

Question 7

Give a strength of research into circadian rhythms.

Answer 7

One strength of research into circadian rhythms is that is provides an understanding of the adverse consequences that occur when they are disrupted. For example, night workers engaged in shift work experience a period of reduced concentration around 6 in the morning (a circadian trough) meaning mistakes and accidents are more likely. Shift workers are also three times more likely to develop heart disease than those with typical work patterns. This shows that research into the sleep/wake cycle may have real-world economic implications in terms of how best to manage worker productivity.

Question 8

Counterpoint to the practical application of research into circadian rhythms.

Answer 8

Studies investigating the effects of shift work tend to be correlational methods which means it is difficult to establish whether desynchronisation of the sleep/wake cycle is actually a cause of negative effects or their may be other factors.
For example, Solomon found 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 it may not be biological factors that create the adverse consequences associated with shift work.

Question 9

Limitation of research into circadian rhythms.

Answer 9

One limitation of research into circadian rhythms is that generalisations are difficult to make. Studies such as Siffre and Aschoff and Wever are based on very small samples of participants and we are aware that sleep/wake cycles vary from person to person. Duffy found that some people have natural preferences for going to bed early and rising early whereas others prefer the opposite. Even Siffre observed that his sleep/wake cycle had slowed down since he was a young man. This means it is difficult to use the research data to discuss anything more than averages which can be meaningless.

Question 10

How long do infradian rhythms last for?

Answer 10

They have a frequency of less than one in 24 hours.

Question 11

Give an example of an infradian rhythm.

Answer 11

The menstrual cycle.

Question 12

What is the menstrual cycle?

Answer 12

The cycle refers to the time between the first day of a woman’s period, when the womb lining is shed, to the day before her next period. During each cycle, rising levels of the hormone oestrogen cause the ovary to develop an egg and release it (ovulation). After ovulation, the hormone progesterone helps with womb lining grow thicker. If pregnancy does not occur, the egg is absorbed into the body and the womb lining comes away and leaves the body.

Question 13

Evidence to suggest that the menstrual cycle is governed by exogenous factors.

Answer 13

A study by Stern and McClintock studied 29 women with a history of irregular periods. Samples of pheromones were gathered from nine of the women at different stages of their cycle, via a cotton pad on their armpit. The pads were worn for at least 8 hours to ensure that pheromones were picked up. The pads were treated with alcohol and frozen, to be rubbed on the upper lip of other participants. On day one, pads from the start of the menstrual cycle were applied to all 20 women, on day two they were given a pad from day two and so on. They found that 68% of women experienced changes within their cycle which brought them closer to the cycle of their ‘odor donor’.

Question 14

What is the frequency of an ultradian rhythm?

Answer 14

More than one cycle in every 24 hours.

Question 15

Give an example of an ultradian rhythm.

Answer 15

The sleep cycle.

Question 16

How long is the average sleep cycle?

Answer 16

90 minutes

Question 17

What happens in stage 1 and 2 of the sleep cycle?

Answer 17

These are light sleep when a person may easily be woken up.

Question 18

What happens in stages 3 and 4 of the sleep cycle?

Answer 18

This is known as deep sleep or slow-wave sleep. It is difficult to wake someone at this point.

Question 19

What happens in stage 5 of the sleep cycle?

Answer 19

Rapid eye movement (REM) occurs. This is the stage where dreams are most often experienced.

Question 20

Give a strength of research into infradian and ultradian rhythms (evolutionary basis).

Answer 20

One strength of menstrual synchrony research is that it may be explained by natural selection. Synchronisation of the menstrual cycle is thought to have evolutionary value. For our distant ancestors, it may have been advantageous for women to menstruate together and become pregnant at the same time. This would allow babies who had lost their mothers during or after childbirth to have access to breastmilk, therefore increasing their chances of survival. This suggests that synchronisation is an adaptive strategy.

Question 21

Give a strength of research into infradian and ultradian rhythms (improved understanding).

Answer 21

One strength of research into ultradian rhythms is that it has improved understanding of age-related changes in sleep. Sleep scientists have observed that the sleep wake cycle reduces with age. Growth hormone is mostly produced during the sleep wake cycle therefore this reduces in older people. According to Cauter et al. the resulting sleep deficit may explain various issues in old age such as altetness. This suggests that knowledge of ultradian rhythms has practical value.

Question 22

Give a limitation of research into infradian and ultradian rhythms (methodological limitations).

Answer 22

There are many factors which may effect and change the menstrual cycle, including stress, changes in diet, exercise etc. These may act as confounding variables which means that any supposed pattern of synchronisation is no more than by chance. This may explain why other studies have struggled to replicate the findings of Stern and McClintock. This suggests menstrual synchrony studies are flawed

Question 23

Give a limitation of research into infradian and ultradian rhythms (individual differences)

Answer 23

One limitation of ultradian rhythms research is there is significant variation between people Tucker found large differences between participants in terms of the duration of each sleep stage. This suggests that these differences are likely to be biologically determined. This makes it difficult to describe ‘normal sleep’ in any meaningful way.