biological rhythms: infradian rhythms Flashcards
what is an infradian rhythm?
type of biological rhythm with a frequency of less than one cycle in 24 hours
what does the menstrual cycle refer to?
- the time between the first day of a period, when the womb lining is shed, to the day before the next period
- governed by monthly changes in hormone levels which regulate ovulation
how long is a menstrual cycle?
- 28 days typically
- anywhere between 24 and 35 is considered normal
describe the menstrual cycle
- rising levels of oestrogen cause ovary to develop an egg and release it (ovulation)
- after ovulation, progesterone helps the womb lining to grow thicker, readying the womb for pregnancy
- if pregnancy does not occur, the egg is absorbed into the body
- womb lining comes away and leaves body (menstrual flow)
is the menstrual cycle endogenous or exogenous?
- endogenous system
- however, evidence suggests that it may be influenced by exogenous factors, such as the cycles of other women
what did stern and mcclintock (1998) demonstrate?
how menstrual cycles may synchronise as a result of the influence of pheromones
stern and mcclintock: procedure
- 29 women with a history of irregular periods
- samples of pheromones were gathered from 9 of the women at different stages of their menstrual cycle, via a cotton pad placed in their armpit
- the pads were worn for at least 8 hours to ensure the pheromones were picked up
- pads were treated with alcohol, frozen, to be rubbed on the upper lip of the other participants
- on day 1, pads from the start of the menstrual cycle were applied to all 20 women, on day 2, they were all given a pad from the 2nd day of the cycle and so on
stern and mcclintock: findings
68% of women experienced changes to the cycle which brought them closer the cycle of the women whose pheromones were applied
what is seasonal affective disorder (SAD)?
- depressive disorder which has a seasonal pattern of onsent
- described and diagnosed as a mental disroder in the DSM-5
what are the main symptoms of SAD?
- persistent low mood
- general lack of activity and interest in life
when can symptoms of SAD be triggered?
during the winter months when the number of daylight hours becomes shorter
what type of biological rhythm is SAD?
- particular type of infradian rhythm called a circannual rhythm as it is subject to a yearly cycle
- can also be classed as a circadian rhythms as the experience of SAD may be due to disruption of SWC which can be due to prolonged periods of daily darkness in winter
what might be a cause of SAD?
- hormone melatonin is implicated
- during the night, the pineal gland secretes melatonin until dawn when there is an increase in light
- during winter, the lack of light in the morning means this secretion process continues for longer
- this is thought to have a knock-on effect on the production of serotonin the brain, a chemical that has been linked to the onsent of depressive symptoms
evaluation: menstrual synchrony may be explained by natural selection
- evoluntionary value
- for ancestors, it may have been advantageous for women to menstruate together and become pregnant at the same time
- in a social group, this would allow babies who had lost their mothers during or after childbirth to have access to milk, thereby improving their chances of survival
- therefore, synchronisation is an adaptive strategy
evaluation: synchronisation studies have methological limitations
- many factors may cause changes to the menstrual cycle eg. stress, changes in diet, exercise etc.
- these may act as confounding variables, so any supposed pattern of synchronisation is no more than would have been expected to occur by chance
- this may explain why other studies (eg. trevathan et al. 1993) have failed to replicate the findings
- this suggests that menstrual synchrony studies are flawed
