Biopsychology: Effect Of EP And EZ On The Sleep-Wake Cycle Flashcards
What Are Endogenous Pacemakers?
- Internal body clocks that regulate many of our biological rhythms.
What Are Exogenous Zeitgebers?
External cues that may affect or entrain our biological rhythm.
The Suprachiasmatic Nucleus (SCN) And The Pineal Gland.
- It is an endogenous pacemaker.
- Located in the hypothalamus.
- Influential in maintaining circadian rhythms.
- Regulated by light from the environment, it receives information about light even when your eyes are closed.
- Passes information on day lengths and light to pineal gland.
- During the night the pineal gland produces melatonin which is a chemical inducing sleep and is inhibited during periods of wake.
Endogenous Pacemaker Research: DeCoursey et Al.
Procedure: Destroyed the SCN connections in the brain of 30 chipmunks who then returned to their natural habitat and observed for 80 days.
Findings: The sleep-wake cycle of the chipmunks disappeared and by the end of the study a significant proportion of them had been killed by predators because they were awake and vulnerable to attack when they should have been asleep.
Conclusion: This shows how important the SCN is in regulating the sleep-wake cycle.
Endogenous Pacemaker Research: Ralph Et Al.
Procedure: Created ‘mutant’ hamsters who had a 20 hour sleep-wake cycle. Transplanted the SCN cells from the mutant hamsters into the brains of normal hamsters (24 hour sleep-wake cycle).
Findings: The normal hamsters following transplantation ended up on a 20 hour sleep-wake cycle.
Conclusion: This shows the role of the SCN in establishing and maintaining the sleep-wake cycle.
Exogenous Zeitgebers In More Detail.
- There are external cues that may affect or entrain our biological rhythms such as the influence of light on the sleep-wake cycle.
- Zeitgebers set our body clocks through entrainment (synchronisation of our body to the environment).
- With a free running body clock (no external cues) we have a sleep-wake cycle but it is not 24 hours.
- External and internal cues work together to determine our 24 hour cycle.
Exogenous Zeitgebers - Light
- Light resets the SCN and can also effect hormone secretion and blood circulation.
Exogenous Zeitgebers - Light (Campbell And Murphy).
- Campbell and Murphy showed that light can be detected by skin receptor sites on the body even when the same information is not received by the eye.
- 15 participants were woken at various times and a light pad shone on the back of their knees.
- Researcher produced a deviation in the participants’ usual sleep-wake cycles and it was up to 3 hours in some cases.
- Suggests that light is a powerful EZ that influence brain and body.
- Practical application: need to be sleeping in a dark room and should not have any artificial light.
Exogenous Zeitgebers - Social Cues.
- Schedules that are imposed on us by society and are key influences on our sleep-wake cycle e.g times we eat, times we go t bed.
- Entrainment of the body following jet lag is quicker when people eat and sleep when the local culture do rather than responding to your own body and feelings of hunger and feelings.
Exogenous Zeitgebers Evaluation: Weakness - Other Complex Influences.
- Research into SCN may draw attention away from research into other body clocks.
- Damiola et al showed how changing feeding patterns in mice altered circadian rhythms of cells in the liver for up to 12 hours, leaving the rhythm of the SCN unaffected.
- This suggests there may be other complex influences on the sleep/wake cycle, aside from the master clock, SCN.
Exogenous Zeitgebers And Endogenous Pacemakers Evaluation: Weakness - Generalisability.
- There are many differences between humans and animals that could impact on the sleep-wake cycle.
- Cognitive factors may be more significant in humans.
- Generalising findings from research into the sleep-wake cycle from animal studies is problematic.
Endogenous Pacemaker Evaluation: Weakness - Ethical Issues.
- There are ethical issues of researching the sleep/wake cycle of animals.
- In DeCoursey’s research the animal were exposed to great harm and potential risks when returned to their natural habitat with a significant proportion of them killed by predators.
- What we learn from investigations on biological rhythms may not justify the adverse procedure involved.
Endogenous Pacemaker Evaluation: Strength - Cause And Effect.
- The use of animal research does allow us to establish cause and effect which is an aim of science.
- In DeCoursey’s study the chipmunks had their SCN connections destroyed and were then released into their habitat.
- It is likely the inability to function when released was the result of what had happened to their SCN.
- This would be unethical to conduct with humans and would mean that we would not know about the effect of the SCN on the sleep-wake cycle had this research not been completed.
Exogenous Zeitgebers Evaluation: Weakness - Overstated.
- The influence of EZ may be overstated.
- Individuals who live in Arctic regions (where the sun does not set during the summer months) show normal sleep patterns despite prolonged exposure to light.
- This suggests there are occasions when EZ may have little bearing on our internal rhythms.
Exogenous Zeitgebers Evaluation: Weakness - Methodological Issues.
- There are methodological issues in EZ research.
- Campbell and Murphy’s study has yet to be replicated and is criticised because there may have been some light exposure to participant’s eyes - a major confounding variables.
- Isolating one EZ (light) in this way does not give insight into the many other zeitgebers that influence the sleep/wake cycle.
- This suggests that some studies may have ignored or underplayed the way in which different exogenous zeitgebers interact.
