Evaluation of Exogenous Pacemakers and Exogenous Zeitgebers

• strengths

  • research support from animal studies for the role of the SCN
  • research support from humans for influence of light
  • practical applications for jetlag
• research support from animal studies for the role of the SCN 


  morgan (1995)
• research support from animal studies for the role of the SCN COUNTER ARGUMENT 


  it is difficult to generalise findings of the sleep-wake cycle from animals onto humans
• research support from humans for influence of light 


  campbell and murphy (1998)
• research support from humans for influence of light COUNTER ARGUMENT 


  it has been suggested that there may have been some limited light exposure to the participants' eyes and acted as a confounding variable. also isolating one exogenous zeitgeber (light) in this way does not give us insight into the many other zeitgebers that influence the sleep-wake cycle and the extent to which these may interact
• practical applications for jetlag 


  burgess et al. (2003)- volunteers participated in one of three treatments before an east-west flight; (continuous bright light, intermittent bright light and dim light), each of which shifted their sleep-wake cycle back by 1 hour a day over 3 days-> those exposed to the continuous bright light prior to the flight needed less time to readjust to the local time on arrival. this suggests that light exposure prior to a flight would allow travellers to arrive with their circadian rhythms already partially re-adjusted to local time
• limitations 


  influence of exogenous zeitgebers may be overstated
• influence of exogenous zeitgebers may be overstated

  • miles et al (1977)-> a young man, blind from birth, with a circadian rhythm of 24.9 hours. despite exposure to social cues, his sleep-wake cycle could not be adjusted and he had to take sedatives at night and stimulants in the morning to keep pace with the 24-hour world
  • similarly, studies of individuals who live in arctic regions show normal sleep patterns despite the prolonged exposure to light
  • both of these examples suggest that there are occasions where exogenous zeitgebers may have little bearing on our internal rhythm