circadian rhythms

• biological rhythms

  -these are regular patterns of physiological behaviour/cognitive activity
• circadian rhythms

  -biological rhythms, they are a cycle that last 24 hours
• sleep/wake cycle

  -the sleep/wake cycle lasts 24 hours: asleep and awake for one period of time in this 24 hours

  -contributes to when we feel tired and alert

  -sleepiest at 2-5am; most alert at 9-11am

  -this cycle is governed by internal factors (endogenous pacemakers) and external factors (exogenous zeitgebers)

  -internal factors: SCN which gives information about light levels

  -external factors: light levels & social cues

  -different neurotransmitters are released at different times of this cycle e.g., melatonin being released before going to sleep
• Siffre (1975)

  -case study of himself

  -6 months in a cave, no natural light, no clock/cues about time of day

  -let his internal body clock run free

  -it settled into a cycle of 25-30 hours

  -he lost track of time, thought he was in the cave for 5 months, not 6

  -relied on internal factors

  -found that endogenous pacemakers (internal factors) are good at regulating the body to the 24 hour cycles but exogenous zeigebers (external factors) are needed to fully regulate us

  -AO3: extraneous variable - artificial light. Acted as an external factor. Case study, cannot be generalised.
• Aschoff & Wever (1976)

  -ppts in an old WW2 bunker for 4 weeks with no natural light

  -most ppts had a sleep/wake cycle of 25-27 hours but 1 ppt had the cycle of 29 hours

  -internal factors are good at regulating the sleep/wake cycle but external factors are needed to make this 24 hours

  -there are individual differences in the circadian rhythm
• Folkard et al (1985)

  -12 ppts in a cave with no natural light for 3 weeks

  -ppts were given a clock, this clock was sped up so the day was only 22 hour, ppts did not know this

  -only 1 ppt was able to adjust the pace of the clock

  -found that internal factors are more important than external for the sleep/wake cycle
• core body temperature - another example of circadian rhythm

  -body temp is at its lowest in the early hours of the morning: 36 degrees

  -body temp is its highest in the early evening: 38 degrees

  -sleep normally happens when the body temp drops

  -melatonin is released before sleep when the temp starts to decrease
• Boivin et al (1996)

  -people who work night shifts have decreased alertness during their shifts, from midnight-4am

  -more likely to make mistakes/have accidents

  -hard to override the sleep/wake cycle (circadian rhythms)
• Recht et al (1995)

  -looked at baseball teams from different states

  -teams going from west to east were more likely to win compared to people going from east to west

  -west to east (phase alert) & east to west (phase delay)

  -sleep/wake cycle is hard to override
• circadian rhythms - AO3

  Strength(s):

  -evidence for CR controlling behaviour. Siffre (1975): s/w cycle 25-30h. Controlled his behaviour e.g., when to wake/sleep. D: case study, can't generalise/little population validity.

  -RWA: researchers have said that school should start later to fit in with the s/w cycle of teenagers. D: economic implications - people work, can't take children to school later. Despite this, research into CR has use.

  
  

  Weakness(es):

  -hard to generalise. Small samples/case studies. D: lots of studies have been done that got similar results. Are reliable but lack population validity.