Circadian rhythms Flashcards
What are biological rhythms?
Distinct patterns of changes in body activity that conform to cyclical time periods
What are biological rhythms influenced by?
Endogenous pacemakers and exogenous zeitgebers
What are endogenous pacemakers?
Internal body clocks
What are exogenous zeitgebers?
External changes to the environment
What is a circadian rhythm?
A type of biological rhythm which is subject to a 24 hour cycle that regulates a number of different body processes such as the sleep/wake cycle and changes in core body temperature
Siffre (1975) aim:
To investigate the influence of light as an exogenous zeitgeber on circadian rhythms
Siffre (1975) procedure:
A case study where Siffre lived underground to study his own circadian rhythms. While living underground he had no external clues to guide his biological rhythms - no daylight, clocks or radio.
He simply woke, ate and slept when he felt it was appropriate to do so. The only thing influencing his behaviour was his internal body clock.
He would take observations such as blood pressure and memory tests.
Siffre (1975) results:
He found that his STM was affected and his periods of sleep wake cycle were longer than 24 hours and varied from 18-52 hours.
Siffre (1975) conclusion:
Exogenous zeitgebers can affect humans natural sleep/wake cycle
Natural sleep/wake cycle may be slightly longer than 24 hours but it is entrained by exogenous zeitgebers associated with the 24 hour day.
Folkard et al. (1985):
Studied a group of 12 people in a dark cave for 3 weeks who went to bed when the clock red 11:45 and woke up at 7:45. Over the study the experimenters slowly sped up the clock so the day only lasted 22 hours. Only 1 participant was able to adjust to the shortened day which suggests the existence of a strong free running circadian rhythm which cannot be easily overridden by changes in the external environment.
Evaluate research into circadian rhythms: generalisability
Conducted on individuals or small groups which may mean the findings lack generalisability to the target population.
Results gained from idiographic studies should not be applied nomothetically to generate general laws of behaviour, as such results are likely to lack population validity.
Evaluate research into circadian rhythms: control
Can be criticised for poor control
Lack of standardisation - some studies people were deprived of natural light, some still had access to natural light. This means we cannot compare findings from these studies and we cannot easily replicate to ensure reliability
Evaluate research into circadian rhythms: individual differences
There are individual differences in circadian rhythms which makes it difficult to generalise as cycles can vary from anywhere between 13 and 65 hours.
Duffy et al (2001) revealed that some people are naturally larks and some people are owls.
Evaluate research into circadian rhythms: practical applications
Good practical applications
Has helped in the understanding of the adverse effects of desynchronisation.
Bovin et al (1996) found that night shift workers experience a reduction in concentration at 6am (a circadian trough) meaning they are more likely to make mistakes or have accidents.
What has research suggested about shift work?
Relationship between shift work and poor health
Knuttson (2003) found that shift workers are three times more likely to develop heart disease, which may be in part due to the stress associated with adjusting to different sleep/wake patterns and lack of quality sleep during the day.
What are two examples of the relationship between endogenous pacemakers and exogenous zeitgebers breaking down?
Jet lag and shift work
What is phase delay in terms of jet lag?
When your endogenous pacemaker is ahead of local time and has to wait for local zeitgebers to catch up
What is phase advance in terms of jet lag?
When your endogenous pacemaker is behind and has to ‘catch up’
Why do symptoms of jet lag occur?
Due to the dislocation of endogenous pacemaker from local exogenous zeitgebers
What has night shift work been linked to?
Increased frequency of car accidents and increased risk of heart problems
How has research into circadian rhythms impacted pharmokinetics?
Research into circadian rhythms has revealed that there are peak times during the day or night when drugs are likely to be the most effective which has led to guidelines being developed regarding the dosing of certain drugs including anti-epileptic medication
