Mindmap on Biological Rhythms

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  • Biological Rhythms
    • Definition: any change in biological activity that repeats periodically.
    • Circadian Rhythms: rhythms with a cycle of 24 hours.
      • e.g sleep wake cycle- In any 24 hour period, we go to sleep and wake up.
      • Core body temperature: It changes during a 24 hour cycle; lowest at 4.30am and highest around 6.00pm
      • Hormones: Melatonin and growth hormone both peak at midnight.
      • Main research: Siffre. He spent 6 months in an underground cave, separated from natural light- dark cycles. He was wired up so his bodily functions could be recorded. When he was awake, researches put lights on and off when asleep.
        • Findings: At first, his sleep-wake cycle was erratic, but then settled to a pattern of around 25-30 hours. When he emerged from the cave it was the 179th day but in his days it was only the 151st.
          • Conclusion: Our biological clocks can work on their own but don't work effectively without exogenous zeitgebers as it runs slightly slower than 24 hours.
        • Supporting research: Aschoff and Weber: isolated ppts. in an underground WW2 bunker for 3-4 weeks at a time. All ppts followed a circadian rhythm with a sleep wake cycle of around 25 hours.
    • Infradian Rhythms: Biological cycles of longer than 24 hours.
      • E.g menstrual cycle- driven through fluctuating hormones and an egg is released approximately every 28 days. Normally governed by endogenous pacemakers but can be controlled by exogenous cues
        • McClintock: observed menstrual cycles among dorm mates became synchronised. She concluded this was due to pheromones (odourless substance)
          • Did a follow up study on 29 women aged 20-35 by gathering pheromones from 9 of the women by placing cotton pads under their arms. Pad was then frozen, treated in alcohol to disguise smell and then placed under women's noses on a daily basis.
            • Found: 68% of women responded to pheromones: cycle either shortened from 1-14 days or lengthened from 1-12 days to be similar to the donor of pad.
              • McClintock: observed menstrual cycles among dorm mates became synchronised. She concluded this was due to pheromones (odourless substance)
                • Did a follow up study on 29 women aged 20-35 by gathering pheromones from 9 of the women by placing cotton pads under their arms. Pad was then frozen, treated in alcohol to disguise smell and then placed under women's noses on a daily basis.
                  • Found: 68% of women responded to pheromones: cycle either shortened from 1-14 days or lengthened from 1-12 days to be similar to the donor of pad.
                  • Evaluation: Russel found supporting research for McClintock. Support also comes from animal evolution, lionesses synchronise pregnancies so another can feed their young if something happens to them.
                    • Negative: Methodological issues; many studies use small samples and reply on women recalling the onset date of menstruation which may be innacurate.
                      • A study examining a woman's basketball team found no correlation between women's menstrual patterns.
            • Evaluation: Russel found supporting research for McClintock. Support also comes from animal evolution, lionesses synchronise pregnancies so another can feed their young if something happens to them.
              • Negative: Methodological issues; many studies use small samples and reply on women recalling the onset date of menstruation which may be innacurate.
                • A study examining a woman's basketball team found no correlation between women's menstrual patterns.
      • Ultradian rhythms: cycle of less than 24 hours.
        • Basic Rest Activity cycle: 90 minute cycle within 24 hour circadian cycle. For example eating and drinking
          • Friedman & Fisher: observed and drinking behaviour in participant over 6 hours. they detected a clear 90 minute cycle in eating and drinking behaviour.
          • Klein & Armitage: found ultradian rhythms in using brain- 96 minute cycle in participants performance on verbal and spatial tasks.
            • However artificial and uncomfortable surroundings of sleep lab could reduce ecological validity.
              • Evaluation: data is sound and empirical and has been tested + found reliable.
        • Sleep stages: short cycles of REM and NREM within circadian rhythm.
          • Dement & Kleitmen: demonstrated link between REM and dreaming. found a 92 minute involving alternation between REM and NREM.
        • Bollini et al; shows up ultradian temperature fluctuations in many babies (would rise and dip more than once a day)
          • Evaluation: data is sound and empirical and has been tested + found reliable.
        • Klein & Armitage: found ultradian rhythms in using brain- 96 minute cycle in participants performance on verbal and spatial tasks.
          • However artificial and uncomfortable surroundings of sleep lab could reduce ecological validity.
      • Circadian Rhythms: rhythms with a cycle of 24 hours.
        • e.g sleep wake cycle- In any 24 hour period, we go to sleep and wake up.
        • Core body temperature: It changes during a 24 hour cycle; lowest at 4.30am and highest around 6.00pm
        • Hormones: Melatonin and growth hormone both peak at midnight.
        • Main research: Siffre. He spent 6 months in an underground cave, separated from natural light- dark cycles. He was wired up so his bodily functions could be recorded. When he was awake, researches put lights on and off when asleep.
          • Findings: At first, his sleep-wake cycle was erratic, but then settled to a pattern of around 25-30 hours. When he emerged from the cave it was the 179th day but in his days it was only the 151st.
            • Conclusion: Our biological clocks can work on their own but don't work effectively without exogenous zeitgebers as it runs slightly slower than 24 hours.
          • Supporting research: Aschoff and Weber: isolated ppts. in an underground WW2 bunker for 3-4 weeks at a time. All ppts followed a circadian rhythm with a sleep wake cycle of around 25 hours.
      • Positive: many other studies have found a 25 hour cycle. Miles reported a 24.9 cycle for a man who was blind from birth.

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