A03 - Endogenous Pacemakers & Exogenous Zeitgebers

• Evaluation Points of EP & EZ?


  -Ethics & generalisability

  -Case Study Evidence (Miles et al 1977)

  -EP can’t be studied in isolation

  -SCN & other influences

  -EZ differ in different environments

  +Real Life application

  +Age related insomnia
• Weakness of EP & EZ - Combine ethics & generalisation together - PART 1


  P: Issues of ethics of Animal studies and (application) generalising them to humans.

  E: Animal studies of sleep/wake cycle are justified coz there are similar mechanisms in all mammals so generalisations can made to human brain, but they still not human & thus results from them not be generalised & thus low external validity.
• Weakness of EP & EZ - Combine ethics & generalisation together - PART 2


  E: Disturbing issues are ethics involved. E.G. DeCoursey study exposed animals to considerable harm & subsequent risk when returning them to wild most died as result.

  L: Suggests studies like these can't be justified & researchers should find alternative ways of studying endogenous pacemakers, since for many, knowledge gained from research will never justify means & such research should thus never be permitted.
• Case Study Evidence - Weakness of EZ & EP? - PART 1

  P: Another limitation in case study evidence undermines effects of exogenous cues.

  E: Case study evidence Miles et al (1977) contradicts influence of exogenous zeitgebers. Reporting case of a man, blind from birth, with abnormal normal circadian rhythm of 24.9 hours.
• Case Study Evidence - Weakness of EZ & EP? - PART 2

  E: Despite exposure to social cues, like mealtimes, his sleep/wake cycle could not be adjusted (struggled). He had take sedatives at night & stimulants in morning to function in a 24 hour world.

  L: Suggesting social cues alone not effective in resetting biological rhythm & natural body clock is stronger (EZ of social cues had no bearing on entraining his natural circadian rhythm).
• SCN & other influences - Weakness of EZ & EP?


  P: One limitation of SCN research is that it may obscure other body clocks.

  E: Body clocks (Peripheral oscillators) are found in many organs and cells (e.g. lungs, skin). They are highly influenced by the actions of the SCN but can act independently.

  E: Damiola et al (2000) showed how changing feeding patterns in mice altered circadian rhythms of cells in the liver for up to 12 hours, leaving SCN unaffected.

  L: This suggests there may be many other complex influences on the sleep/wake cycle aside from the master clock (SCN).
• Real life applications - strength of EP & EZ?


  P: Application of research is alleviation of symptoms of jet lag which caused by body’s internal clock being out of step with external cues.

  E: E.G. travellers could stay awake until they get to their normal bedtime in new country allowing them to adapt to new time zone.

  E: Also, period of fasting before travel followed by eating at times relevant to new time zone is effective.

  L: Shows we can entrain our bodies to new time zone more quickly by adjusting our bodies drive to sleep & eat (EP) to be more in line with light & social cues (EZ).
• EP cant be studied in isolation - Weakness of EZ & EP?
- PART 1


  INTERACTIONIST VIEW

  P: Another limitation is in reality EPs are rarely free-running or unaffected by EZ, thus EP can not be studied in isolation.

  E: Only in exceptional circumstances are EPs ‘free running’ and unaffected by the influence of exogenous zeitgebers since most circadian rhythms are affected by an interaction of EPs and EZs.
• EP cant be studied in isolation - Weakness of EZ & EP?
- PART 2


  E: Total isolation studies (e.g. Siffre cave study) are rare and lack external validity. In everyday life, pacemakers and zeitgeber interact so it may make little sense to separate the two.

  L: Therefore it makes no sense to separate them out for the purposes of research. This suggests the more researchers attempt to isolate the influence of internal pacemakers, the lower the validity of the research.

  (Very complex. Studying them separately - simplistic view).
• EZ differ in different environments - weakness of EP & EZ?

  P: One limitation is effects of EZ differ in different environments,

  E: Exogenous zeitgebers do not have the same effect on people who live in places where there is very little darkness in summer and very little light in winter.

  E: For instance, the Innuit Indiancs of the Arctic Circle have similar sleep patterns all-year round, despite spending around 6 months in almost total darkness.

  L: This suggests the sleep/wake cycle is primarily controlled by endogenous pacemakers that can override environmental changes in light.
• Age related insomnia - strength of EZ & EP?


  P: Age-related insomnia

  E: Natural changes in circadian rhythms mean older people fall asleep early and have poorer quality sleep (Duffy et al 2015).

  E: However, Hood et al (2004) found that management of insomnia improved if elderly people were more active and had more exposure to natural light during the day,

  L: This suggests that exogenous changes in lifestyle may be just as likely to cause age-related insomnia as internal biological changes. 
• Evaluation points of EP & EZ?

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