Circadian Rhythms

• Circadian rhythm 


  -refers to the cyclical or rhythmic change in biological processing, mood or behaviour that takes approximately 24 hours to complete a full cycle.

  -e.g. sleep wake cycle and core body temperature.

  -Characterised by one peak and one trough during a full day/night period. Each person has their own chronotype which is a natural time someone will wake up.

  -It's determined by genetics but also shifts as we age and is influenced by our environment. e.g. night shifts.
• Sleep - wake cycle

  -is an example of a circadian rhythm.

  -Within a 24h time frame we experience prolonged period of fatigue and so sleep followed a prolonged period of wakefulness, which will repeat the following day.

  -Cortisol levels also peak and trough during a 24 hour period - it peaks at 8am and troughs at 12pm.

  -Core temperature peaks at 10pm and troughs at 4am.

  -Sleep-wake cycle secretes melatonin, peaks at 3am and troughs 8am.

  -Shift workers experience troughs in concentration and alertness during the night.
• Ultradian Rhythms

  -are any cyclical or rhythmic changes in mood, behaviour or physiological processes that occur numerous times within 24hours. Takes less than 24h to complete.

  -e.g. sleep cycle, eating behaviour (fullness/hunger) and meal patterns.
• Research support - Bunker experiment

  -Aschoff and Wever studied 26 students

  -In a temperature controlled, no natural light and food delivered at random times so they couldn't guess what time it is om the outside world.

  -One individual had sleep-wake cycle of 32.6 hours for sleeping.

  -Supports Siffre and argument that endogenous pacemakers can regulate the circadian rhythm, but the exogenous zeitgebers needed to entrain circadian rhythm. -However, low population validity - issues with generalising about CR from students. Influence of age on CR so low ecological validity.
• Folkard et al - a case for endogenous pacemakers

  - 12 participants agreed to live in a dark cave for 3 weeks.

  -Retired to bed when clock said 11:45pm and rising when it says 7:45am.

  -However, clock was changed so day became 22h long, deception.

  -Only one could adapt to the new rhythm.

  -Supports influence of endogenous pacemakers that can't be overridden by exogenous zeitgebers.
• Practical applications - desynchronisation

  -Greater understanding as some individuals whose lifestyle is not synchronised with their body clock.

  -Shift work and jet lag leads to desynchronisation - working when the body should be resting.

  -Night shift workers experiences a 'circadian trough' their concentration dips at 5:00am. Resulting in low productivity and increased accidents.

  -However, there is a greater understanding of the ways in which circadian rhythms are regulated and entrained has improved the health of workers and increased productivity.