Circadian Rhythms

what are biological rhythms

distinct patterns of changes in body activities that conform to cyclical time periods

these exert an important influence on the way in which body systems behave

some of these rhythms occur many times during the day (ultradian) or take longer than a day to complete (infradian)

what are biological rhythms governed by

endogenous pacemakers

exogenous Zeitgebers

what are endogenous pacemakers

body’s internal biological ‘clocks’

what are exogenous zeitgebers

external changes in the environment

what are circadian rhythms

type of biological rhythms that lasts for around 24 hours

e.g. sleep/wake cycle and core body temperature

whats the sleep/wake cycle

a type of circadian rhythm that lasts around 24 hours;

governed by an endogenous pacemaker called the suprachiasmatic nucleus (SCN)

and exogenous Zeitgeber (daylight)

whats the suprachiasmatic nucleus (SCN)

bundle of nerve cells located in the hypothalamus in each hemisphere

its the primary endogenous pacemaker in humans and maintains circadian rhythms (sleep/wake cycle)

SCN lies above the optic chiasm which provides SCN info from the eye abt light

this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight when we sleep

aim of Michel Siffre’s study

to study effects on his own biological rhythms

describe study of Michel Siffre

self styled caveman who spent several extended periods underground

deprived of exposure to natural light and sound but had access to food and drink

Siffre resurfaced in mid-sep 1962 after 2 months in the caves

and believed it was mid-August

his biological rhythm settled down to around 25 hours and continued to fall asleep and wake up on a regular schedule

describe Aschoff & Wever 1976 research

p’s spent 4 weeks in a WW2 bunker deprived of natural light

majority p’s displayed a circadian rhythm between 24 -25 hours

only one p sleep/wake cycle extended to 29 hours

what did Siffre and Aschoff&Wever’s study suggest

suggest that the ‘natural’ sleep/wake cycle may be slightly longer than 24 hours

but its entrained by exogenous zeitgebers associated with our 24 hour routine in a day

(e.g. number of daylight hours/typical mealtimes/etc)

strength of circadian rhythms - provides excellent support for interactionist approach, demonstrating that behaviour is shaped by both nature/nurture

E; The internal biological clock (nature) drives a continuous circadian rhythm as shown in Michel Siffre’s study, where he lived without external cues and his ‘free running’ sleep/wake cycle extended to 25 hours. However exogenous zeitgebers (external cues) like daylight (nurture) are essential to ‘reset’ this internal clock back to 24 hours

E; This illustrates that human biological rhythms are neither purely innate nor entirely socially constructed. Instead they require close interaction of both endogenous pacemakers and exogenous zeitgebers to function normally

L; Therefore, research into circadian rhythms highlights the complexity of human biology, supporting the interactionist approach over deterministic biological or environmental views

strength of investigating circadian rhythms it that it has practical economic applications

E; Bolvin et al found that night shift workers experience a significant decrease in concentration around 6AM leading to increased work place accidents

Knutsson 2003 also suggested that shift workers are 3x more likely to develop heart disease than people who work more typical work patterns

E; By understanding the physiological troughs of the circadian cycle, employers can redesign shift patterns to minimise desynchronisation, which boosts worker productivity and limits dangerous accidents.

L; therefore, the study of circadian rhythms provides highly beneficial real world economic implications in terms of how to best manage worker productivity

limitation of research into circadian rhythms suffer from low ecological validity

E; Aschoff&Waver’s bunker studies required p’s to live in isolated, artificial environments deprived of nature light

E; These environments are strictly controlled and unnatural, so it becomes challenges to apply these findings to everyday life.

L; Therefore, the low ecological validity in many circadian rhythm studies reduces the accuracy and generalisability of findings to real world scenarios

limitation of research into circadian rhythms ignores individual differences

E; Aschoff &Waver and Siffre are based on limited sample sizes but Czeisler et al 1999 found individual differences in sleep/wake cycles varying from 13 to 65 hours.

and Duffy et al 2001 found that some ppl have a natural preference for going to bed early and rising early whereas others prefer the opposite

E; This means that its difficult to generalise findings of research that rely on small sample sizes, as they ignore individual differences

L; Therefore, the research into circadian rhythms appears to follow the nomothetic approach, as they create general laws and assume they apply to everyone.