Infradian Rhythms

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  • Created by: rhallett
  • Created on: 15-11-15 12:28
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  • Infradian Rhythms
    • These rhythms take longer than 24 hours, examples include menstruation, SAD and hamster testosterone
    • Menstrual Cycle
      • takes approx. 28 days, release of an egg and preparation of the uterus for pregnancy. Under the internal control of hormones, oestrogen and progesterone, secreted by the ovaries. no. of factors also involved
      • Light - Reinberg studied a young woman who spent 3 months in a cave in dim light; her MC shortened to 25.7 days; light affects MC
        • -Hard to generalise, involved only 1 person who may have been unusual
        • -3 months is too short a period to determine whether someone's MC has changed as they can be irregular
      • Pheromones - Research shows that women who spend a lot of time together find their MCs become closer and more converged, possibly due to the unconscious secretion of pheromones during the MC
        • Russel had female sweat rubbed below their nose; eventually their cycles converged with that of the sweat donors
          • MC synchrony ay have evolved as it may have been adaptive for females to be fertile at the same time so they could produce young together and help rear them - this argument is speculative however
          • This research has problems so it may not be reliable: -MCs are irregular, so may not really be converging. -Research on lesbian couples living together has not found the same results which suggests the findings are not reliable
    • Seasonal Affective Disorder (SAD)
      • Infradian rhythm that has a yearly cycle; people who have SAD feel depressed in the winter and recover during the summer
      • It is thought that SAD is caused by low light levels in the winter. Could result in an excessive production of melatonin in vulnerable people which leads to depression; effect on a person's serotonin levles
      • Terman studied 124 RPs with SAD, some were exposed to bright light, the other (placebo) were exposed to neg. ions. Bright light group had significant improvement with their SAD
        • +Clear practical application, suggess SAD can be treated using light therapy, uses light boxes which emit between 6-10k lux and person sits in front of it. Can also treat depression, compared to anti-depressants it has v few side effects.
      • SAD is more common in places further away from the Equator where there are shorter days in winter. Rosen found increased SAD in more N parts of the US compared to S
        • -Some research hasn't found this; Magnusson found that despite Iceland being a notably N country, it doesn't have high levels of SAD
    • Hamster Tesosterone Cycle
      • Some evidence taht the SCN plays a role in regulating Infradian rhythms. Male H's have a yearly cycle of T secretion which is disrupted if the SCN in destroyed.
        • -It is not clear whether these results show that the SCN plays a role in human rhythms as hamsters have a different biology to humans.


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