Circadian rhythms AO1

• Circadian rhythms

  •Last for about 24 hours

  •Two examples – sleep/wake cycle and core body temperature

  •Sleep-wake cycle is a circadian rhythm which dictates when we should be asleep and awake
• Sleep/wake cycle

  •Feeling drowsy at night

  •Alert during the day – shows the effect of daylight – exogenous zeitgeber
• Siffre's cave study

  •Siffre spent 6 months living in a cave with no natural light or anyone to tell him what time of day it was

  •His biological clock was allowed to ‘free-run’ – allowed his body’s inclinations (eating & sleeping whenever he chose with no fixed timetable)

  •Wired up so some of his body functions could be recorded

  •Had a telephone link to the outside world & was monitored by video camera
• Siffre's cave study - conclusion

  we do have an internal mechanism that regulates our sleep/wake cycle, but it shifts to approximately 25 hours if we don’t have exogenous zeitgebers such as lights and meal times to reset it
• Aschoff and Wever

  •Got a group of pp’s to spend 4 weeks in a WWII bunker deprived of natural light

  •All but one pp displayed a circadian rhythm between 24-25 hours

  •Both studies suggest that the natural sleep/wake cycle may be slightly longer that 24 hours

  •It is entrained by exogenous zeitgebers associated with the 24 hour day (daylight hours, meal times etc)
• Folkard et al

  A group of 12 pp’s lived in a dark cave for 3 weeks, going to bed when the clock said 11.45pm and rising when it said 7.45am

  Over the course of the study the researchers sped up the clock

  A 24 hour day eventually only lasted 22 hours

  Suggests existence of a strong free-running circadian rhythm that cant easily be overridden by changes to the external environment
• Core body temperature

  •Core body temperature varies by around 2 degrees centigrade during the course of the day

  •Lowest at 4am (36 degrees C)

  •Peaks around 6pm (38 degrees C)

  •Body temperature may affect mental abilities – the warmer we are internally, the better our cognitive performance

  •Folkard et al (1977) - children who had stories read to them at 3pm showed superior recall & comprehension than those who heard stories at 9am

  •Gupta (1991) – found improved performance on IQ tests when were pp’s were assessed at 7pm rather than 2pm and 9am