Biological Rhythms: Infradian and Ultradian Rhythms

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  • Biological Rhythms: Infradian and Ultradian Rhythms
    • Infradian Rhythms
      • a type of biological rhythm with a frequency of less than one cycle in 24 hours.
      • female menstrual cycle - rise in oestrogen causes ovary to develop an egg, progesterone causes womb lining to grow thicker
      • McClintock showed how menstrual cycles synchronise when influenced by female hormones
        • 29 women with irregular periods - 9 women gave their pheromones via cotton pad under armpit
          • pads were rubbed on upper lip other pps - 68% experienced changes to their cycle
      • SAD - depressive disorder with a seasonal pattern of onset. Melatonin is implicated and can affect production of serotonin in the brain
        • is an infradian rhythm called a circannual rhythm as it is subject to a yearly cycle
    • Ultradian Rhythms
      • a type of biological rhythm with a frequency of more than one cycle in 24 hours
      • Sleep/wake cycle - 5 distinct stages of sleep that altogether span approx 90 mins.
        • Stages 1 and 2 - light sleep, easily woken, brainwave patterns become slower and more rhythmic
        • Stages 3 and 4 - involve delta waves which are slower and have a greater amplitude, slow wave sleep
        • Stage 5 - aka REM sleep, the body is paralysed yet brain activity speeds up
    • Evaluation
      • menstrual synchrony is thought to have evolutionary value
        • it can be advantageous for females to menstruate together
      • criticisms have been made of early synchronisation studies and the methods employed. Confounding variables eg stress may affect a womans cycle
        • research typically involves small samples of women and relies on pps self reportong the onset of their own cycle
      • Dement and Kleitman found that REM activity highly correlated with the experience of dreaming
        • also suggests that REM is an important component of the ultradian sleep/cycle

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