Circadian Rhythms

Question 1

What is a circadian rhythm? Give an example.

Answer 1

A biological rhythm that typically lasts 24 hours, such as the sleep wake cycle.

Question 2

The sleep wake cycle is controlled by what endogenous pacemaker?
Describe how it works.

Answer 2

The superchiasmatic nucleus (SCN).
Receives information from the eye about light, which is sent through the optic nerve to the SCN.

Question 3

The sleep wake cycle is governed by which exogenous zeitgeber?
How?

Answer 3

Light.
The darker it is, the less light received by the SCN, telling the hypothalamus and then the pineal gland to secrete more melatonin.

Question 4

What was the aim of Siffres cave study?

Answer 4

To study how lack of light affects his own biological rhythms.

Question 5

What research method did Siffre use?

Answer 5

Case study

Question 6

Describe the procedure of Siffre’s study.
What was the duration of the study?

Answer 6

He deprived himself of light, sound and external social cues by living in a cave for 2 months. He only had access to food and drink.

Question 7

Describe the findings from Siffre’s study.
(How long was his new circadian rhythm?
What did he still do on a regular schedule?)

Answer 7

His circadian rhythm lengthened to 25 hours, however, he still slept and woke on a regular schedule.

Question 8

What can we conclude from Siffre’s experiment?

Answer 8

Deprivation of light and sound increases the circadian rhythm.

Question 9

Describe the procedure for Aschoff and Wever’s WW2 study.
Give the duration of the study.

Answer 9

Convinced PPTs to spend 4 weeks living in a WW2 bunker deprived of natural light.

Question 10

Describe the findings from Aschoff and Wever’s experiment.

Answer 10

All PPTs had a circadian rhythm of 24/25 hours, except 1 PPTs whose rhythm extended to 29 hours.

Question 11

What can we conclude about the length of the sleep/wake cycle from Aschoff and Wever’s experiment?
How is the length of the cycle entrained?

Answer 11

The natural sleep/wake cycle may be closer to 25 hours but that is entrained by exogenous zeitgebers associated with a 24-hour day (such as daylight, mealtimes etc).

Question 12

Give the procedure of Folkard’s study. (Shortening day)
What was the duration of the experiment?

Answer 12

Studied a group of 12 people who agreed to live in a dark cave for 3 weeks. They went to sleep at 11:45pm everyday when a clock said so and woke when the clock said 7:45am. Over the course of the study, researchers (unknown to PPTs), gradually sped up the clock so the 24-hour day lasted 22 hours.

Question 13

Give the findings from Folkards study.

Answer 13

Only 1 PPT was able to adapt to the new regime.

Question 14

What conclusion can we make from Folkards study?

Answer 14

The circadian rhythm cant be easily overcome by exogenous zeitgebers.

Question 15

Explain the benefit of increasing our understanding circadian rhythms on shift workers.
What health conditions can shift work lead to?
Can shift work have economic implications?

Answer 15

For example, night workers engaged in shift work experience a period of reduced concentration at 6am, meaning mistakes and accidents are more likely. Research has also shown a link to shift work and poor health. Shift workers are 3 times more likely to develop heart conditions than people who work normal shift patterns. This means that the sleep wake cycle may have real world economic implications.

Question 16

Explain the benefit of research into circadian rhythms improving medical treatments.
What are chronotherapeautics and how are they beneficial for reducing the risk of illnesses, such as heart attacks?

Answer 16

Circadian rhythms coordinate several of the body’s basic processes such as heart rate. This has lead to the development of chronotherapeutics, where medical treatment is administered in a way that corresponds to a person’s biological rhythm. For example, aspirin as a treatment for heart attacks is most effective when taken late at night. Aspirin reduces blood platelet activity which reduces risk of heart attack. This shows that research into circadian rhythms can help increase the effectiveness of drug treatments.

Question 17

Explain the limitation of there being methodological issues with research into circadian rhythms.
Use the example of Siffre’s case study and Aschoff and Wever’s small sample size.
Explain the issues with confounding variables, where PPTs in these studies had access to natural light.

Answer 17

For example, Siffre used a case study, which is highly specific to himself. This means his findings are not generalisable to whole populations, therefore his research lacks population validity. Additionally, Aschoff and Wever used a small sample size, which again means their research lacks population validity. Also, PPTs in these studies had access to natural light. More light means less melatonin produced, giving the impression that the sleep/wake cycle is longer. This means that there are issues with confounding variables, so findings overall may be invalid.

Question 18

Explain the limitation of the impact individual differences between PPTs can have (such as age).
Use the examples of owls/larks and age.
Use another example from Cziesler who discovered variations in the length of sleep/wake cycles.

Answer 18

For example, age can have influence on the sleep/wake cycle. Older people are more likely to wake/sleep earlier, whereas adolescents are more likely to wake/sleep later, which is a result of our natural melatonin production. Cziesler found that individual differences can cause huge differences in sleep wake cycles, varying from 13 to 65 hours. These individual differences are often ignored in studies, so the findings may not be truly reflective of entire populations.