Circadian Rhythms Flashcards
What is a Circadian Rhythm
A type of biological rhythm subject to a 24-hour cycle
which regulates a number of body processes such as the sleep/wake cycle and changes in core body temperature
The Sleep/Wake Cycle
Daylight is an important exogenous zeitgeber as we feel drowsy when it’s night-time and alert during the day
Siffre’s Cave Study
Michael Siffre spent several extended periods underground to study the effects on his own biological rhythms
He was deprived of exposure to natural light and sound, but had access to adequate food and drink
He resurfaced in mid-September 1962, after two months in the caves of the southern Alps, believing it to be mid-August
A decade later, he performed a similar feat, but this time for six months in a Texan cave
In each case, his 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
Aschoff and Wever (1976)
Convinced a group of participants to spend four weeks in a World War II 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 experience and the bunker study suggest that the natural sleep cycle may be slightly longer than 24 hours but that it is entrained by exogenous zeitgebers associated with a 24-hour day
Folkard et al (1985)
Studied a group of 12 people who agreed to live in a dark cave for three weeks retiring to bed when the clock said 11:45 pm and rising when it said 7:45 am
Over the course of the study, the researchers gradually sped up the clock without the participants knowing so an apparent 24 hour day eventually lasted only 22 hours
Only one of the participants was able to comfortably adjust to the new regime
Suggest the existence of a strong, free running circadian rhythm that cannot easily be overridden by changes in the external environment
Evaluation (STRENGTH) - Practical Application to Shift Work
Has given research as a better understanding of the adverse consequences that can occur as a result of their disruption
Boivin et al (1996)
Night workers experience a period of reduced concentration around 6 am meaning mistakes and accidents are more likely
Knutson (2003)
Research has suggested a relationship between shiftwork and poor health
Shift workers are three times more likely to develop heart disease, which may partly be due to the stress of adjusting to a different sleep/wake pattern and the lack of poor quality sleep during the day
May have economic implications in terms of how best to manage worker productivity
Evaluation (STRENGTH) - Practical Application to Drug Treatments
Research has revealed there are certain peak times during the day or night, when drugs are likely to be at their most effective
Baraldo (2008)
Led to the development of guidelines to do with the timing of drug dosing for a whole range of medication including anti-cancer, cardiovascular, respiratory, anti-ulcer and anti-epileptic drugs
Evaluation (WEAKNESS) - Case Studies and Small Samples
People involved may not be representative of the wider population limiting the extent of meaningful generalisations
In his most recent cave experience Siffre was 60 and observed that his internal clock ticked much more slower now than when he was a young man
Illustrates that even when the same person is involved, there are factors that vary which may prevent general conclusions being drawn
Evaluation (WEAKNESS) - Poor Control in Studies
Although participants were deprived of natural light, they still had access to artificial light
Czeisler et al (1999)
Was able to adjust participants circadian rhythms from 22 to 28 hours using dim lighting
The use of a light may be analogous to participants taking a drug that resets their biological clock
Evaluation (WEAKNESS) - Individual Differences
Individual cycles can vary complicating the generalisation of findings
Duffy et al (2001)
Found that some people display a natural preference for going to bed early and rising early where some people prefer to do the opposite
There are also age difference in sleep/wake patterns
