circadian rhythms (biological rhythms)

• Biological rhythms:

  • biological rhythms are periodic activity, governed by:
  • Internal biological ‘clocks’ (endogenous pacemakers)
  • External changes in the environment (exogenous zeitgebers)
• circadian rhythms:

  • about one cycle every 24 hours
  • Eg = sleep/wake cycle
• sleep/wake cycle governed by internal and external mechanisms:

  • EZs = the fact we feel drowsy when it’s night-time and alert during the day shows the effect of daylight
  • EPs = a biological clock ‘left to its own devices‘ without the influence of external stimuli (eg light) is called ‘free-running’
  • The basic rhythm is governed by the SCN = which lies above the optic chiasm which provides information from the eyes about light
  • EZs (eg light) can reset the the SCN
• Siffre demonstrated a free-running circadian rhythm of about 25 hours:

  • French caver Siffre spent long periods in dark caves to examine the effects of free-running biological clocks
  • 2 months AND 6 months
  • In each case study = Siffre’s free-running circadian rhythm settled down to about 25 hours AND he had a regular sleep/wake cycle
• Aschoff and Wever found a similar circadian rhythm:

  • A group of participants spent 4 weeks in a WW2 bunker deprived of natural light
  • All but one (whose sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24 and 25 hours
  • Siffre’s experience and the bunker study suggest that the ‘natural’ sleep/wake cycle may be slightly longer than 24 hours but is entrained by EZs associated with our 24-hour day (eg daylight hours, mealtimes)
• Folklard et al = showed EPs stronger than EZs

  • He studied a group of 12 people who lived in a dark caves for 3 weeks = going to bed when clock said 11:45 pm and waking up when it said 7:45 am
  • unbeknown to the participants = the researchers gradually sped up the clock to a 22-hour day
  • Only one participant comfortably adjusted to the new regime
  • This suggests the existence of a strong free-runnning circadian rhythm not controlled by EZs
• strength = application to shift work

  • Shift work creates desynchronisation of biological rhythms
  • Bolvin et al = found shift workers experienced a lapse of concentration 6 am (a circadian trough) so accidents are more likely
  • Research also suggests a link between shift workers and poor health = with shift workers 3 times more likely to develop heart disease
  • => research into sleep/wake cycle may have economic implications in terms of how best to manage shift work
• counterpoint to application to shift work

  • The research is correlational
  • => desynchronisation may not be the cause of observed difficulties
  • Eg = Solomon concluded that high divorce rates in shift workers might be due to missing out on important family events
  • Suggests that it may not be biological factors that create the adverse consequences associated with shift work.
• strength = RWA to medical treatment

  • Circadian rhythms co-ordinate the body’s basic process (eg heart rate, hormone levels) with implications for chronotherapeutics (timing medication to maximise the effects on the body)
  • Aspirin reduces heart attacks = which are most likely in the morning
  • Bonten et al = found taking aspirin is most effective last ting at night
  • Shows that circadian rhythm research can help increase the effectiveness of drug treatments
• limitation = generalisations are difficult to make (idiographic approach)

  • Studies of the sleep/wake cycle often use small groups of participants (eg Aschcoff and Wever) or even single individuals (eg Siffre)
  • Participants may not be representative of the wider population and this limits making meaningful generalisations
  • Siffre observed that his internal clock ticked much more slowly at 60 than when he was younger
  • Suggests that, even when the same person is involved, there are factors that may prevent general conclusions being drawn
• extra evaluation = shifting the school day

  • Research showed benefits for teenagers‘ academic and behavioural performance when lessons start later in the day
  • BUT = a later start is disruptive for parents and teachers AND teenagers may simply stay up later and still be exhausted
  • Suggests that changing the school day may not be practical even though it may be desirable