circadian rhythms

• biological rhythms

  • al living organisms subject to biological rhythm that exert important influence on way body behaves
  • governed by internal body clock (endogenous pacemakers) + external changes in environment (exogenous zeitgebers)
  • some rhythms occur many times in a day (ultradian) other longer than a day to complete (infradian) and some much longer (circannual)
  • circadian rhythms last 24 hours
  • e.g: sleep/wake cycle + core body temp
• Sleep/wake cycle

  • Feeling drowsy at night and alert in day demonstrated effects of daylight (exogenous zeitgeber)
  • Governed by internal (endogenous) pacemaker – biological ‘clock’ called suprachiasmatic nucleus – lies just above optic chiasm (provides information from the eye about light), light can reset the SCN
  • researchers tried to answer what would happen if we don’t have external factors such as light
• Siffre’s cave study

  • Siffre a cave man who spend extended periods of periods underground to study effects on his own biological rhythms
  • deprived of exposure to sunlight + sound for 2 months in caves of Southern Alps
  • resurfaced mid-September 1962 believing it was August
  • performed similar study for 6 months in Texan cave
  • free-running biological rhythm settled down to one just beyond usual 24hrs - continued to fall asleep + wake in regular schedule
• Folkard et al

  • 12 people in dark cave for 3 weeks with a clock (bed = 11:45pm, wake = 7:45am)
  • researchers secretly speed up clock so 24hours becomes 22 hours
  • only 1 person able to adjust comfortably
  • shouldn’t overestimate influence of exogenous zeitgebers
• Aschoff + Wever

  • convinced group of participants to spend 4 weeks in WW2 bunker deprived of natural lightall but 1 participants showed circadian rhythm of 24-25hours (1 showed 29)
  • all but 1 participants showed circadian rhythm of 24-25hours (1 showed 29)
  • suggests natural sleep/wake cycle slightly greater than 24 hours but entrained by exogenous zeitgeist's associated with 24-hour day
• evaluations

  • S: understanding consequences of disrupted rhythms: Bovin et al: night workers engaged in shift-work have periods of reduced concentration at 6am (circadian trough) meaning mistakes + accidents more likely + develop heart disease more than those with tropical patterns - real world economic implications HOWEVER use correlation: difficult to establish wether desynchronisation of sleep/wake cycle causes of negotiable effects, Solomon: high divorce rate in shift workers might be due to strian of deprived sleep + other influences (missing out on events) - may not be biological factors
• evaluations

  • S: used to improve medical treatment: rhythms co-ordinate a number of the body’s basic processes that rise and fall during the day, leads to chronotherapeutics (how medical treatment can be administered to correspond to biological rhythms) – e.g. aspirin for heart problems taken at night as heart attacks are more common early in the morning - research can help increase effectiveness of drug treatment
• evaluations

  • S: Wolfson + Carkadon: school day starts couple hours later to accommodate for typical teenage chronotype – hormonal shifts mean getting to sleep becomes more difficult + adolescents tend to be more tired during the morning – benefits for academic + behavioural performance when lessons start later in the day
• evaluations

  • W: generalisations: Aschoff + Wever and Siffre’s research based on small samples, sleep/wake cycles vary from person to person. Czeisler et al: individual differences in cycles vary from 13 to 65 hours + Duffy et al: some people have natural preference for going to bed early and rising early (larks) whereas others are the opposite (owls) + Siffre: observed his own cycle slowed down since he was a young man.                                                                   —> difficult to use research data to discuss anything more than averages - meaningless