Discuss research into circadian rhythms


Circadian rhythms are biological cycles that last around 24 hours such as the sleep-wake cycle. It is suggested that this circadian rhythm is free running and controlled by endogenous pacemakers (internal body clock).  However, there is also evidence that the circadian rhythm can be altered by external environmental cues, called exogenous zeitgebers. Two examples of circadian rhytms are the sleep/wake cycle and core body temperature, which is lowest at around 4:30am (36 degrees) and highest at 6pm (38 degrees). 

Evidence to support the role of the endogenous pacemaker stems from Siffre's cave study (1972).  Siffre investigated the effect of removing all external cues on the circadian sleep-wake cycle.  Siffre spent 7 months underground in a cave without any natural light, clocks or radio; he simple ate and slept when he felt like it. His body eventually settled into a 25 hour circadian rhythm despite the eradication of external cues, from this we can conclude that the circadian rhythm is free running and will persist despite the removel of external cues.

Siffre’s case study is supported by Aschoff and Wever who conducted 205 isolated  laboratory experiments. Small groups of students were placed underground in a WWII bunkers in the absence of exogenous zietgebers. They discovered that most of the participants continued to display circadian rhythms between 24-25 hours, although some were as long as 29 hours.

A strength of this study is that both endogenous pacemakers and exogenous zietgebers are accounted for- representing both sides of the ‘nature, nurture debate.’ Thus, it could


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