Biological rhythms: Circadian rhythms Flashcards
Biological rhythms
Circadian rhythms
All living organisms are subject to bio rhythms
All bio rhythms governed by endogenous pacemakers & exogenous zeitgebers
Some occur many times in a day (ultradian) while others take longer than a day (infradian)
Circadian rhythms last for around 24hrs
E.g. sleep/wake cycle & core body temp
Sleep/wake cycle
Circadian rhythms
We feel drowsy at night & alert during day because of effect of daylight on our s/w cycle
s/w cycle also governed by suprachiasmatic nucleus (SCN) (bio clock)
SCN lies just above optic chiasm which provides infro from eye about light
Light can reset SCN
Siffre’s cave study
Circadian rhythms
Siffre spent several extended periods underground to study effects of his own biological rhythms
Deprived on nat light & sound but w/ access to adequate food & drink
He spent 2 months in cave in Alps
A decade later he spent 6 months in a Texan cave
In both cases, his ‘free-running’ bio rhythm settled to around 25 hours
He still fell asleep and woke up on a regular schedule
Aschoff & Wever (1976)
Circadian rhythms
Convinced group pf ppts to spend 4 weeks in WW2 bunker, deprived of nat light
All but 1 ppt (whose s/w cycle extended to 29 hours) displayed a circadian rhythm between 24 & 24 hours
Both Siffre’s experience & bunker suggest that ‘nat’ s/w cycle may be slightly longer than 24 hours but is entrained by exogenous zeitgebers associated w/ our 24 hour day
Folkard et al (1985)
Circadian rhythms
A group of 12 ppts who lived in a dark cave for 3 weeks retiring to bed at 11:45pm and rising at 7:45am (displayed on a clock)
Over course of study, researchers gradually sped up the clock so they day only lasted 22 hours by the end
It was revealed that only one ppt was able to comfortably adjust to new regime
Suggests existence of strong free-running circadian rhythm that cannot easily be overridden by exogenous zeitgebers
Evaluation: Shift work
Circadian rhythms
Strength: provides understanding of adverse consequences that occur in desynchronisation
E.g. night workers experiences a period of reduced conc around 6am (circadian trough) meaning mistakes are more likely (Boivin et al)
Research pointed to relationship between shift work & poor health - shift workers 3x more likely to develop heart disease (Knutsson 2003)
Therefore, research into s/w cycle may hve real-world economic implications in termss of managing worker productivity
Evaluation: Shift work (Counterpoint)
Circadian rhythms
However, studies investigating effects of shift work tend to use correlational methods
Means its difficult to establish whether desynchronisation of s/w cycle is actually a cause of neg effects
Solomon concluded that high divorce rates in shift workers may be due to strain of deprived sleep & other influences such as missing out on family events
Therefore, bio factors may not create adverse consequences associated w/ shift work
Evaluation: Medical treatment
Circadian rhythms
Strength: been used to improve medical treatments
Circadian rhythms coordinate body’s basic processes (i.e. heart reat & digestion)
These rise & fall during course of a day which led to field of chronotherapeutics - how medical treatment can be administered in way thet corresponds to person’s biological rhythms
E.g. aspirin as treatment for heart attacks is most effective if taken last thing at night
Aspirin reduces blood platelet activity & this can reduce risk of heart attack
Heart attacks are most likely to occur in morning so timing of taking aspirin matters (Bonten et al 2015)
Therefore, circadian rhythm research can help increase effectiveness of drug treatments
Evaluation: Individual differences
Circadian rhythms
Limit: generalisations are difficult to make
Aschoff & Weave and Siffre are based on small samples of ppts
Seems s/w cycles vary widely person to person
Czeisler et al found individual diffs in s/w cycles varying from 13-65 hours
Duffy et al revealed some people have natural preference for going to bed early & rising early whereas others prefer opposite
Siffre observed his own s/w cycle slow down as he got older
Therefore, it’s difficult to use research data to discuss anything more than averages, which may be meaningless
