Discuss the role of endogenous pace makers and/or exogenous zeitgebers in infradian rhythms (9+16)

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Discuss the role of endogenous pace makers and/or exogenous zeitgebers in infradian rhythms (9+16)


Infradian rhythms are biological cycles lasting more than 24 hours, like the menstrual cycle, which is regulated by hormone secretions (Follicle Stimulating Hormoneand Leutenising Hormone) Originally it was thought to be controlled by the hypothalamus acting as an endogenous pacemaker however, evidence has shown that exogenous zeitgebers play a part too. Infradian rhythms do not have to be monthly and can apply to behaviour. That occur once a year, some people suffer from a depressive condition called SAD during winter months and recover during summer.
SAD (Seasonal Affective Disorder) sufferers experience severe symptoms from seasonal changes such as lowering moods and depression which is thought to be brought about due to less sight and increased melatonin and low levels of serotonin has been linked with chronic depression.
Reinberg reported on a woman who spent 3 months in a cave without natural lighting. Her menstrual cycle shortened to 25.7 days, implying that infradian rhythms are influenced by exogenous zeitgebers such as light cues.


However, living in a cave means it has low Ecological validity and is not representative of natural settings. Therefore results may not necessarily mean changes were due to the absence of light, as temperature, smell and noise could all have contributed in some form and other extraneous variables could not be ruled out.
Russell et al applied underarm sweat of donor women to the upper lips of female participants, finding that menstrual cycles became synchronised, supporting McClintock, suggesting pheromones act as exogenous zeitgebers and can influence…


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