A01

• A circadian rhythm is a biological rhythm that lasts for around 24 hours and is governed by internal factors, such as the suprachiasmatic nucleus (endogenous pacemakers), and external actors, such as light (exogenous zeitgebers). Two examples of circadian rhythms are the sleep/wake cycle and core body temperature.
• The sleep/wake cycle is controlled by our internal biological clock, or SCN, which uses light information (exogenous zeitgeber) to reset itself every day. Siffre conducted a study to investigate the importance of light on our circadian rhythm. He spent several months underground, deprived of natural light and sound. He found that his biological rhythm settled down to around 25 hours. He concluded that our internal clock is free running and doesn’t need external influences such as daylight.
• Our core body temperature fluctuates by about two degrees during the course of the day, with its lowest at 4AM (36°) and peaks around 6PM (38°). Body temperature has shown to impact cognitive abilities - Gupita (1991) showed an improved performance on IQ tests when assessed at 7pm compared to 2pm and 9am.