Circadian rhythms

What are circadian rhythms, and what are two key examples?

Circadian rhythms are biological cycles that last about 24 hours. Examples include the sleep/wake cycle and body temperature fluctuations

What is the role of the suprachiasmatic nucleus (SCN) in circadian rhythms?

The SCN is an endogenous pacemaker located in the hypothalamus. It acts as the body’s master clock, regulating circadian rhythms like sleep and wakefulness, and is reset by light.

Who conducted a famous cave study on circadian rhythms, and what did he find?

Michel Siffre spent extended periods underground. He found that his “free-running” sleep/wake cycle settled to around 25 hours, suggesting an internal clock slightly longer than 24 hours.

What did Aschoff and Wever (1976) find in their bunker study?

Participants deprived of natural light settled into a circadian rhythm of 24–25 hours, supporting the idea that endogenous rhythms exist but are influenced by external cues.

What did Folkard et al. (1985) discover about overriding the circadian clock?

When they artificially shortened the day to 22 hours, only 1 of 12 participants could adjust, showing the circadian rhythm is strong and difficult to override with external cues alone.

What are the practical implications of circadian rhythm disruption for shift workers?

Shift work can lead to a “circadian trough” around 6 a.m., increasing mistakes and accidents. It’s also linked to higher risks of heart disease and relationship strain.

How has circadian rhythm research improved medical treatment?

It led to chronotherapeutics—timing medications to match body rhythms. For example, aspirin is most effective at night to reduce morning heart attack risk.

Why might individual differences limit the conclusions of circadian rhythm research?

Studies often use small samples, and people vary widely in cycle length and chronotype (e.g., “larks” vs. “owls”), making it hard to generalize from averages.

What is one proposed application of circadian rhythm research in education?

Some researchers suggest starting school later for teenagers, whose hormonal shifts delay sleep, to improve academic performance and reduce sleep deprivation

What are the two main factors that govern biological rhythms?

Endogenous pacemakers (internal biological clocks like the SCN) and exogenous zeitgebers (external cues like light and social routines).