Circadian Rhythms

• Circadian rhythms are biological rhythms that regulate bodily processes in a 24 hour cycle
• 2 circadian rhythms are the sleep/wake cycle and body temperature
• A biological rhythm is a distinct pattern of changes in body activity that conform to cyclical time periods
• Michel Siffre (1962)- Cave Study:

  Aim: to find influence natural sleep-wake cycle of no exogenous zeitgebers

  Findings: Spend twice as long as expected in cave; warped sense of time

  • Free running- biological rhythms not running according to environmental cues
  • 2 months living in total isolation in subterranean cave without access to clock, calendar or natural sunlight
• Aschoff & Wever (1976):

  • Participants spent 4 weeks in bunker deprived of natural light during WWS
  • All participants but one (sleep/wake cycle of 29 hours) displayed a circadian rhythm of 24-25 hours
  • Sleep/wake cycles may be slightly longer than 24 hours but entrained by exogenous zeitgebers
• Folkard et al. (1985):

  • Studied 12 people who agreed to live in a dark cave for 3 weeks- going to bed when clock said 11:45pm and waking up at 7:45am; researchers gradually sped up clocks (participants not aware); day only became 22 hours
  • Findings revealed 1/12 able to comfortably adjust to 22-horu day; suggested existence of strong free-running circadian rhythm that cannot be overridden by change in external environment
• Body Temperature:

  • Human body temp is at its lowest in the early morning (36C at 4:30am) and highest in early evening (38C at 6:00pm)
  • Sleep occurs when core temp starts to drop, body temp starts to rise at end of sleep cycle, promoting alertness
  • Body temp may have an effect on mental abilities; the warmer we are, the better our cognitive performance
• Body Temperature:

  • Folkard et al (1977) demonstrated children read stories at 3pm showed superior recall/ comprehension after a week when compared to those read stories at 9am
  • Gupta (1991) found improved performance in IQ tests when participants were assessed at 7pm as opposed to 9am and 2pm
• S- Practical application (CR):

  Researchers have a better understanding of adverse consequences that can occur as a result of desynchronisation. Night workers engaged in shift work experience a period of reduced concentration at 6am, meaning mistakes and accidents are more likely (Boylin et al.). Research also suggests a relationship between shift work and poor health: shift workers 3x more likely to develop heart disease (Knutsson, 2003) which may be due to stress of adjusting sleep/wake cycle. Economic implications in terms of how to best manage worker productivity
• S- Practical application to drug treatment (CR):

  Circadian rhythms co-ordinate a number of bodily processes like heart rate, digestion and hormone levels; effect on pharmacokinetics- the action of drugs on the body and how well they are absorbed/ distributed. There are peak times during the day/night when drugs are most likely to be effective. Led to development of guidelines to do with timing of drug dosing for medication like anticancer, respiratory and cardiovascular (Baraldo, 2008)
• S- Research support (CR):

  Research conducted investigating circadian rhythms and effect of external cues like light on systems. Siffre (1975) found absence of external cues significantly alerted his circadian rhythm; when returned from cave found little difference in his sleep/wake cycle