Exogenous zeitgebers/Endogenous pacemakers AO3 AO3

RS from Ralph et AAl(+)

• Took the SCN from a ‘mutant hamster’ who had a circadian rhythm that mutated to 20 hours. They transplanted the mutant SCN into the brains of normal adult hamsters

• The normal hamsters took on the circadian rhythms of the mutant hamsters. Despite the shortcomings of less scientific case study research findings, EPs do play an important role in regulating the sleep-wake cycle

Limitations of Raph et Al (-)

• There is evolutionary discontinuity between humans and hamsters i.e. hamsters are mostly nocturnal, while humans are not.

• This makes it difficult to extrapolate the findings from research from animal studies to humans.

EZ Contradictory research (-)

• Luce& Segal suggest light levels can be overridden. In the Arctic Circle people still maintain a reasonably constant sleep pattern, averaging 7 hours a night, despite 6 months of darkness in the winter months, followed by 6 months of light in the summer

• In these conditions it appears to be social factors that act to reset endogenous rhythms rather than light levels

EZ: Supporting research (+)

• Vetter et Al investigated the effect of changing lights temperature at the workplace

• Results found that artificial blue-enriched light competes with natural light as a zeitgebers. Subjects working under the warmer light appear to entrain to natural dawn, the subjects exposed to blue-enriched light appear to entrain to office hours

• Confirms that light is the dominant zeitgebers for the human clock. The results also indicate that blue-enriched light is a potent zeitgeber that has to be used with diligence.