infradian rhythm

• less than one every 24 hours
• menstrual cycle is governed by monthly changes in the hormone cycle, which regulates ovulation which occurs every 24-35 days. high levels oestrogen egg release ovulate. after ovulation womb lining thickens if pregnancy not occur the egg is absorbed into body and the womb lining sheds
• synchronising menstrual cycle:

  stern and mcclintock 1998 menstrual cycles synchronise due to the effect of pheremones. 29 women irregular periods. 9 cotton armpit 12 hrs treated with alcohol. pad applied to upper lip on other 20. 68% experience changes to regulation. cycle regulated with odour donor
• +research support for exogenous zeitgebers on the menstrual cycle. reingberg examined women 3 month small cave lamp and cycle shortened from 28 to 25 days. results suggest even though endogenous pacemakers have an influence it can be effected by exogenous zeitgebers. two conclusions: disruption to circadian rhythm causes irregularity, absence pheremones from other women causes irregularity
• -findings can be scrutinised. many factors such as diet and exercise have an impact on menstrual cycle which are confounding variables. its these factors that act as entrainers for the cycle. these confounding variables may be the reason why Trevathan could not replicate the findings of stern and mccclintock. it appears that there are many factors which influence the cycle which needs to be taken account for
• treatment for SAD is light box therapy, which is a box that stimulates strong light and resets the internal clock. sanassi 2014 showed that there was a decreased affects of SAD in 80% ppl. light box therapy is preferred treatment for SAD compared to antidepressants as it is more safe. but light box therapy can produce eye strain and headaches. rohan 2009 recorded relapse rate 46% successive winter 27% control group who just had CBT, showing the effectiveness of light box therapy.
• SAD:

  triggered in winter as less daylight hours which impact circadian rhythm. psychologists hypothesised melatonin is implicated in the cause of SAD. night pineal gland secretes melatonin until dawn. lack of light means more melatonin is secreted impacts serotonin leading to depressive symptoms