Circadian Rhythms Flashcards
Who is Michael Siffre?
A self-styled caveman who has spent several extended periods underground to study the effects on his own biological rhythms.
When and why did Siffre resurface?
Deprived of exposure to natural light and sound, but with access to adequate food and drink, Siffre re-surfaced in mid-September 1962 after 2 months in the caves of Southern Alps believing it to be mid-August.
What happened a decade later?
Performed a similar feat but in a Texan cave for 6 months.
What happened to his biological rhythm?
His ‘free-running biological rhythm settled down to one that was just beyond the usual 24 hours (around 25 hours) though he did continue to fall asleep and wake up on a regular schedule.
Jurgen Aschoff and Rutger Wever (1976)
A group of pps to spend 4 weeks in a WWII bunker deprived of natural light.
All but one of pps (whose sleep/wake cycle extended to 29 hrs) displayed a circadian rhythm between 24 and 25 hrs.
What do both Siffre’s cave study and the bunker study suggest?
The natural sleep/wake cycle may be slightly longer than 24 hrs but it is entrained by exogenous zeitgebers linked with our 24 hour day.
Simon Folkard et al (1985)
Studied a group 0f 12 pps who agreed to live in a dark cave for 3 weeks, retiring to bed when the clock read 11.45pm and woke up when it read 7.45am.
Over course of the study, researchers gradually speeded up the clock (unknown to pps) so an apparent 24 hr day eventually lasted only 22 hours.
Revealed that only one of pps was able to comfortably adjust to the new regime; suggesting the existence of a strong free-running circadian rhythm that can’t easily be overridden by changes in the external environment.
Weakness - poor control in studies
Although pps in the studies were deprived of natural light, they still had access to artificial light.
For instance, Siffre turned on a lamp every time he woke up which remained on until he went to bed. It was assumed by him and others that artificial light, unlike daylight, would have no effect on the free-running biological rhythm. However, in tests, Charles Czeisler et al (1999) were able to adjust pps’ circadian rhythms from 22 to 28 hours using dim lighting. As such, the use of light may be analogous to pps taking is drug that resets their biological clock.
Weakness - individual differences
A further issue that complicates the generalisation of findings from studies of the sleep/wake cycle is that individual cycles can vary, in some cases from 13 to 65 hours (Czeisler et al. 1999). In addition, a study by Jeanne Duffy et al (2001) revealed that some people display a natural preference for going to bed early and rising early - larks - whereas some people prefer to do the opposite - owls. There are also age differences in sleep/wake patterns.
Strength - practical application to shift work
Knowledge of circadian rhythms has given researchers a better understanding of the adverse consequences that can occur as a result of their disruption - desynchronisation.
For instance, 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 (Boivin et al 1996). Research has also suggested a relationship between shift work and poor health: shift workers are 3 times more likely to develop heart disease (Knutsson 2003) which may in part be due to the stress of adjusting to different sleep/wake patterns and the lack of poor quality sleep during the day.
Thus, research into the sleep/wake cycle may have economic implications in terms of how best to manage worker productivity.
Strength - practical application to drug treatments
Circadian rhythms co-ordinate a number of the body’s basic processes such as heart rate, digestion and hormone levels. This in turn has an effect on pharmacokinetics, that is, the action of drugs on the body and how well they are absorbed and distributed. Research into circadian rhthyms has revealed that there are certain peak times during the day or night when drugs are likely to be at their most effective.
This has led to the development of guidelines to do with the timing of drugs dosing for a whole range of medications including anticancer, cardiovascular, respiratory, anti-ulcer and anti-epileptic drugs (Baraldo 2008).
Weakness - use of case studies and small samples
Studies of the sleep/wake cycle tend to involve small groups of pps, as in the experiment by Aschoff and Wever, or studies of single individuals, as in the case of Siffre. The people involved may not be representative of the wider population and this limits the extent to which meaningful generalisations can be made. In his most recent cave experience in 1999, Siffre observed, at the age of 60, that his internal clock ticked much more slowly than when he was a young man. This illustrates the fact that, even when the same person is involved, there are factors that vary which may prevent general conclusions being drawn.
