biological rhythms: circadian rhythms

• biological rhythms


  Patterns of changes in the body activity that conforms to cyclical periods which are influenced by internal factors (endogenous pacemakers) and external factors ( exogenous zeitgebers)
• circadian rhythm


  A biological rhythm that is subject to a 24 hour cycle and regulates a number of bodily processes
• example of a circadian rhythm

  Sleep/wake cycle
• Siffre's research into sleep/wake cycle

  - spent several periods of time underground which led him to being deprived from natural light and sound

  - he spent 2 months in a cave in the Southern Alps in which he came out the cave September 1862 believing it was August

  - he also spent 6 months in a texan cave

  - he found that his 'free running' biological rhythm settled down to a 25 hour cycle

  - however , as he fell asleep at regular hours he may have had some light exposure which may have affected sleep

  - this was only done on him as a participant which may not be reliable
• Aschoff & Wever (1976) research into sleep/wake cycle

  - had ppts spend 4 weeks in a WW1 bunker where they were deprived of natural light

  - all but one displayed a circadian rhythm between 24 & 25 hours

  - however one had a 29 hour cycle
• Aschoff & Wever research suggested


  the 'natural' sleep/wake cycle may be slightly longer than 24 hours but it is influenced by exogenous zeitgebers
• Folkard et al (1985)


  - studied a group of people who lived in a cave for 3 weeks who went to bed and 11:45pm and got up at 7:45am

  - during the study the clock was put forward (thought that a 24 hour day only lasted 22 hours)

  - only one of the ppts could comfortably adjust to the new regime
• Folkard et al (1985) suggested...


  the existence of a strong 'free running' circadian rhythm that can't be easily be overriden by changes in the external environment
• AO3= practical application to shift work (strength)

  - disruption of circadian rhythms is called desynchronisation which has negative consequences for people who work night shifts ( research into this increases our understanding)

  
  

  - night shift workers have a period of reduced concentration at 6am which is when mistakes and accident are most likely to happen

  
  

  - there's a link between shift work & poor health (Knutsson (2003) )

  
  

  - above may have real world economic complications for how to manage worker productivity
• AO3= Knutsson (2003) research into links between shift work & poor health (strength)


  shift workers are more likely to develop heart disease which could be due to the stress of having to adjust to different sleep/wake patterns and poor quality sleep during the day
• AO3= practical application to drug treatment (strength)

  - circadian rhythms coordinate some the body's processes ( heart rate , digestion etc) which rise and fall during the day and has led to the field of chronotheraputic

  
  

  - how medical treatments can be given in a way that corresponds with biological rhythms

  
  

  - aspirin is a treatment for heart attacks that is most effective when taken at night

  - heart attacks are most likely to happen first thing in the morning

  
  

  - proves that circadian rhythm research can help increase the effectiveness of drug treatments
• AO3= shifting the school day (strength)

  - researchers suggest that the school day should start a couple of hours later to fit in with the teenage chronotype

  
  

  - due to hormonal shifts in teenagers it makes it difficult to sleep meaning they are tired in the morning

  
  

  - evidence of better academic and behavioural performance when lessons start later in the day , including reduced dependance on caffeine
• AO3= individual differences (weakness)


  - generalisations are difficult to make since we are all different

  - Siffre's study was just about himself

  - Aschoff & Wever study was conducted on a small sample

  - these people may not represent the population and therefore it lacks population validity

  - sleep/wake cycles may vary from person to person

  
  

  - 1999 Siffre carried out research on himself at the age of 60

  - reported his internal clock was much slower than when he conducted similar studies as a young man

  
  

  - shows that research data is difficult to generalise due to individual differences
• AO3= practical application to shift work (weakness)

  - studies looking at shift work uses correlation which means we can't day that desynchronisation caused the negative effects (other factor can be involved)

  - eg. high divorce rates in shift workers due to the strain of deprived sleep and missing out on important family events

  
  

  - shows that it may no be desynchronisation causing negative effects but environmental factors
• Czeisler et al (1999) research suggested..

  the sleep/wake cycle can have the variety can be between 13 & 65 hours
• Duffy et al (2001) research suggested...


  that some people prefer to go to bed early and wake up early (larks) & others prefer to stay up late (owls)
• AO3= shifting the school day (weakness)

  - the shift in the school day could be disruptive

  - some critics say this wouldn't reduce sleep deprivation it would just make teenagers stay up later and still be tired