AO3

• The role of the suprachiasmatic nucleus (SCN) in the sleep-wake cycle is supported by studies on non-humans. For example, SCN neurons from hamsters bred to have abnormally short circadian rhythms were transplanted into normal hamsters, who then displayed the abnormal rhythm too. This supports the importance of the SCN in regulating the 24-hour circadian rhythm.
• Real world application to exogenous zeitgebers jet lag: Burgess found that exposure to bright light on a east west flight pattern meant that people could change their circadian rhythms back by an average of 2.1 hours. Again shows the role of light as a EZ
• Siffre spent 2 months in a dark cave. In the absence of light he developed a sleep–wake cycle of 25 hours. Being close to the standard 24 hours this suggests the influence of endogenous factors, i.e. it supports an innate, biologically determined circadian rhythm because he maintained this rhythm in the absence of external zeitgebers. Was the zeitgeber light that entrained the body to a 24 hour period. (evaluate against methodological problem