infradian rhythm Flashcards
how often is an infradian rhythm?
one cycle is less often than 24 hours
give two examples of infradian rhythms
menstruation and seasonal affective disorder
what is the menstrual cycle?
•it occurs monthly, around 28 days long
•during each cycle, rising levels of the hormone oestrogen cause the ovary to develop an egg and release it (ovulation)
•after ovulation, the hormone progesterone helps the womb lining grow thicker, readying the body for pregnancy
•if pregnancy does not occur, the egg is absorbed into the body, and the womb lining comes away and leaves the body
what is the endogenous pacemaker for the menstrual cycle?
ovaries - oestrogen
what is the exogenous zeitgeber for the menstrual cycle?
hormones- pheromones
how do pheromones impact the menstrual cycle?
female pheromones may cause their period to sync
what was McClintok’s study?
•she involved 29 women with irregular periods
•samples of pheromones were gathered from 9 women at different stages of their cycle by absorbing their swear using a cotton pad under their armpit
•the pads were treated and given to the other participants to rub on their upper lip (day one, sweat from day one and so fourth)
•McClintok found that 68% of women experienced changes to their cycle which brought them closer to the cycle of their ‘odour donor’
•suggests exogenous zeitgebers plays a role
why is it convenient to have women on their periods at the same time?
evolutionary reasons- to have children at the same time, gives the babies a social network, if the mother dies another can take care of the baby, if normadic societies moved around it would be more convenient if all the women were menstruating at the same time
what is seasonal affective disorder?
seasonal low mood (depression) thought to be caused by a disruption of the sleep/ wake cycle due to the prolonged hours of darkness causing increased melatonin production and less serotonin
evolutionary basis of the menstrual cycle
•McClintok’s study seems to suggest that the synchrony is thought to have evolutionary value
•the validity of the evolutionary perspective has been questioned by Schank
•Schank argued that if there were too many women on the same cycles they would be in competition for the highest quality males (therefore lowering the fitness of any potential offspring)
•from this pov, the avoidance of synchrony would appear to be the most adaptive evolutionary strategy and therefore naturally selected
methodological limitations in synchronisation studies
•commentators argue that there are many factors that may effect change in a women’s menstrual cycle like stress, diet changes and exercise that may act as confounding variables
•this means that any patterns of synchronisation (like seen by McClintok) is no more than would have been expected to occur by chance
•in addition, research usually involves small samples of women and relies on the participants self- reporting the onset of their own cycle
•perhaps more critically, other studies (Trevathan) failed to find any evidence of menstrual synchrony in all- female samples
who found no evidence of menstrual synchrony?
Trevathan
strength: animal studies
•the roles of pheromones in animal sexual selection is well documented
•sea urchins release pheromones into the surrounding water so other urchins in the colony will eject their sex cells simultaneously
•in contrast, evidence for the effects in human behaviour remains speculative and inconclusive
practical application - SAD
•one of the most effective treatments for SAD is phototherapy here a lightbox creates a very strong light in the morning and the evening, resetting serotonin levels
•this relieves symptoms in up to 60% of sufferers
•however a placebo effect recorded a 30% increase
•this casts doubt on the chemical influence of phototherapy
limitation: correlation between light and SAD
•saying lack of light causes SAD is too deterministic and reductionist
•higher suicide rates in january may be to multiple events that fall in the western calendar
•there are other financial/ social pressures that occur which may cause SAD
