Circadian rhythms

What is a biological rhythm?

A distinct pattern of changes in body activity that conforms to cyclical time periods

What 2 things are biological rhythms influenced by?

Endogenous pacemakers & exogenous zeitgebers

What is a circadian rhythm?

A type of biological rhythm, subject to a 24-hour cycle, which regulates a number of body processes

What are 2 examples of circadian rhythms?

The sleep/wake cycle & changes in core body temperature

What term is used for when the sleep/wake cycle has the absence of external stimuli (e.g. light) ?

Free-running

Why are psychologists interested in a free running system?

To see whether we would we still fall asleep & wake up at regular times even if we didn’t know whether it was night time or daytime

Who investigated free-running circadian rhythms by spending several periods underground in a cave?

Siffre

When Siffre resurfaced after 2 months, how long did he think he’d been in the cave for?

1 month

After what time period did Siffre repeat his test with a 6 month stint in a cave?

10 years

In each case, Siffre’s free-running biological rhythm settled down to one that was just beyond what time period?

Around 25 hours

What do we call the external factors that entrain our circadian rhythm to our 24 hour day?

Exogenous zeitgebers

What are 2 examples of exogenous zeitgebers?

The number of daylight hours & social cues (e.g. meal & bed times)

What term refers to the disruption to circadian rhythms?

Desynchronisation

Discuss what research has shown about circadian rhythms (16 marks)

Write your AO1 paragraph

• Biological rhythms are distinct patterns of changes in body activity that conform to cyclical time periods, influenced by endogenous pacemakers & exogenous zeitgebers. A circadian rhythm is a type of biological rhythm, subject to a 24-hour cycle, that regulates various body processes (e.g. the sleep/wake cycle & changes in core body temperature).

• Researchers investigated what happens to the sleep/wake cycle without external stimuli (e.g. light), known as free-running, to see if we still sleep & wake on a regular schedule, despite not knowing whether it’s night or day. Siffre studied this by living alone in a cave without access to natural light - after 2 months underground, he thought only 1 month had passed. 10 years later, he repeated his cave stint for 6 months. In both cases, his sleep/wake cycle settled to around 25 hours, although he still slept & woke on a regular basis. This suggests the natural sleep/wake cycle may be slightly longer than 24 hours, but it is entrained by exogenous zeitgebers, such as light & social cues (e.g. meal & bed times).

Discuss what research has shown about circadian rhythms (16 marks)

Write your strength AO3 PEEL (practical & economic implications)

• Point: One strength of circadian rhythms is that research evidence has improved our understanding of the negative consequences of desynchronisation.

• Evidence: For example, night shift workers often experience a dip in alertness around 6AM (circadian trough), increasing the risk of mistakes & accidents.

• Explain: Additionally, they are 3 times more likely to develop heart disease, due to the stress of adjusting to irregular sleep/wake patterns & poor sleep quality.

• Link: As such, this has practical & economic implications, as it can inform strategies to manage worker schedules, improve safety & maintain productivity.

Discuss what research has shown about circadian rhythms (16 marks)

Write your limitation AO3 PEEL (low population validity)

• Point: One limitation of research into circadian rhythms is that studies often have low population validity, as they involve very small sample sizes.

• Evidence: For example, Siffre found his internal body clock ticked more slowly during his second cave stint as an older man compared with his first stint as a younger man.

• Explain: However, individual differences (e.g. age) may influence circadian rhythms, meaning findings may not be representative of the wider population.

• Link: Therefore, the findings may have limited generalisability, making it difficult to draw firm conclusions about human circadian rhythms.

Discuss what research has shown about circadian rhythms (16 marks)

Write your limitation AO3 PEEL (methodological issues)

• Point: One limitation of research into circadian rhythms is that some studies suffer from methodological issues.

• Evidence: For example, in Siffre’s cave stint, he switched on a lamp when he woke up that remained on until he went to bed.

• Explain: It was assumed the artificial light would not affect his free-running biological rhythm. However, Czeisler et al. found that even dim lighting can shift circadian rhythms by 22-28 hours.

• Link: Therefore, this decreases the internal validity of Siffre’s study, as exogenous zeitgebers (e.g. artificial light) may have influenced the findings.