Circadian rhythms

• What is a circadian rhythm

  A circadian rhythm lasts exactly 24 hours, for example sleep-wake cycle and core body temperature cycle
• What is a sleep-wake cycle?

  This refers to the cycle we all have that determines at what time we begin to feel sleepy and go to bed in the evening and at what time we would naturally wake up in the morning. These cycles can vary a lot between people, with some people surviving on as little as 4 hours of sleep a night and some preferring/needing to sleep 10 hours a night. Research conducted into this area investigates how this biological rhythm behaves in isolation to all the things around us, which give us clues about the time (zeitgebers)
• Siffre research

  in 1972 Siffre spent 205 days isolated in Midnight Cave, Texas. Going deep into caves has the advantage of reducing influences on circadian rhythms such as light, temperature and factors that also fluctuate daily. Whilst he could choose to illuminate his living quarters when he wanted to, he had no way of knowing the time in the outside world. Researchers studying his progress found that at first his sleep patterns were erratic but soon settled into a regular rhythm whilst his day shifted to 25 hours long
• Aschoff and Weaver (1976)

  Participants spend up to a month living in specially designed underground laboratories. These 'bunkers' were built to shield participants from any external influence that might affect their circadian rhythms. Participants were allowed to sleep or engage in any activity they wanted. It was noted that they kept a regular cycle of activity, confirming the idea of an internal biological clock. However, this cycle soon began to drift. After about two weeks, participants were found to be half a day out of synchrony with the outside world. It suggested that this was because the body's natural circadian rhythm is closer to 25 hours Without exogenous cues to constantly adjust it, the internal clock became free running- it was not bound to the 24-hour light-dark cycle or entrained by other environmental cues like clocks
• Folkard et al (1985)

  Studied a group of 12 people who lived in a dark cave for 3 weeks. They went to bed when the clock read 11:45 pm and woke up at 7:45 am. During the study, the researcher gradually sped up the clock (participants did not know this), shifting the 24-hour rhythm to a 22-hour rhythm. The findings revealed that none of the participants were able to adjust to the new regime. The conclusion suggests that there is a biologically determined free-running circadian rhythm that cannot be easily overridden by changes in the external environment
• Application of circadian rhythm

  This can be applied to shift work and has explained why people find it difficult to adjust to night shifts. Shift workers are three times more likely to develop heart disease than people who work normal hours. (Knutsson,2003) Work has been done to reduce the impact that shift patterns have on people

  However, Solomon (1993) argues that stress could be causing these effects as shift workers also have higher divorce rates, which may be a consequence of missing family events and being sleep deprived This is impactful because employers could use this information to make the late night shifts more productive as a result increasing their output
• Application of circadian rhythms

  It has been found these changes in bodily processes can be used to better understand how the body absorbs drugs. Chronotherapeutics can apply this to improve drug treatment , this is the study of how the body metabolites drugs at different times. for example aspirin is most effective when taken last thing at night to reduce heart attacks, which are most likely to happen in the morning
• Research limitation of circadian rhythms

  Most of this research is case study or small sample research such as Siffre this is a weakness because it causes a lack of generalizability dut to him being a white, older man as a result it cant be correlated to different ethnicity or ages
• Research limitation of circadian rhythms

  The research often used artificial light to help participants live in their caves/bunkers at the time of research this was not believed to impact on the circadian rhythm at all, however this has now been challenged and could impact on the running of the rhythm this is significant because the confounding variables of artificial lights have an effect on the brain biology
• Theory limitation of circadian rhythms

  There are large individual differences in people's circadian rhythms with some research reporting circadian rhythms lasting from 13-65 hours (Czeisler et al 1999) Age may also pay a role therefore this cannot explain everyone's behaviour