Biological rhythms

• AO1 - circadian rhythms - biological rhythms

  Controlled by internal body clocks (endogenous pacemakers) and external cues (exogenous zeitgebers)
• AO1 - circadian rhythms - sleep/wake cycle

  Governed by daylight and by biological clock (suprachiasmatic nucleus), gets light information from the eyes
• AO1 - circadian rhythms - Siffre's cave study

  His free-running rhythm extended slightly to 25 hours when deprived of daylight
• AO1 - circadian rhythms - other research

  Aschoff and Wever

  Support for exogenous zeitgebers entraining internal clock

  Folkard et al., cave with 22-hour day

  Support for endogenous cues if difference too big
• AO3 - circadian rhythms - shift work

  Boivin et al.

  Reduced concentration at 6 am, more accidents

  Knutsson

  Heart disease three times more likely
• AO3 - circadian rhythms - medical treatment

  Bonten et al.

  Timing of drugs (chronotherapeutics), aspirin more effective at night for heart attack
• AO3 - circadian rhythms - individual differences

  Cycle lengths vary (13 to 65 hours, Czeisler et al.), 'larks' and 'owls' (Duffy et al.), generalisations may be meaningless
• AO3 - circadian rhythms - shifting the school day

  Teenage chronotype means sleepy in morning, so shift school day but disruptive for others
• AO1 - infradian rhythms - the menstrual cycle

  Oestrogen regulates ovulation, progesterone readies body for pregnancy (endogenous factors)
• AO1 - infradian rhythms - synchronising the menstrual cycle

  Stern and McClintock

  Menstrual cycles synchronised through pheromones, exogenous factor
• AO1 - infradian rhythms - seasonal affective disorder

  Form of depression triggered in the winter months and regulated by melatonin, a circannual rhythm
• AO3 - infradian rhythms - evolutionary basis

  Synchronisation may have an adaptive function, leads to shared care for babies
• AO3 - infradian rhythms - methodological limitations

  Trevathan et al.

  Many confounding variables not controlled, so synchronisation may occur by chance
• AO3 - infradian rhythms - real-world application

  Light therapy 80% effective for SAD (Sanassi), but relapse rate is 46% (Rohan et al.) compared to 27% for CBT
• AO1 - ultradian rhythms - stages of sleep

  5 stages that occur in 90-minute cycle:

  Stages 1 and 2: Alpha waves and sleep spindles

  Stages 3 and 4: Deep sleep, delta waves

  Stage 5: REM sleep, theta waves
• AO3 - ultradian rhythms - improved understanding

  van Cauter et al.

  SWS reduces with age, explains issues in old age e.g. reduced alertness
• AO3 - ultradian rhythms - individual differences

  Tucker et al.

  Differences found in duration of each sleep stage, particularly stages 3 and 4
• AO3 - ultradian rhythms - the sleep lab

  Lab studies of sleep control extraneous variables (e.g. noise), but may not represent ordinary sleep patterns