biological rhythms - infradian and ulradian rhythms Flashcards
infradian rhythms - the menstrual cycle
governed by monthly changes in hormone levels which regulate ovulation
cycle is the time between the first day of a women’s period when the womb lining is shed to the day before her next period
typical cycle takes approximately 28 days to complete
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 to grow thicker readying the womb for pregnancy
if pregnancy does not occur the egg is absorbed into the body
the womb lining comes away anf leaves the body (menstrual flow)
infradian rhythms - synchronising the menstrual cycle
menstrual cycle is an endogenous cycle there is evidence that suggests that it may also be included by exogenous factors
such as the cycle of other women
study - Stern and McClintok demonstrated how menstrual cycles may be synchronised as a result of the influence of pheromones
studied 29 women with the history of irregular periods
samples of pheromones where gathered from nine of the women at different stages of their menstrual cycle
done by cotton pad placed on armpit
pads were worn for at least 8 hours to ensure that pheromones were picked up
pads were treated with alcohol and froxen
to be ribbed on the upper lip of other partipcnats
on day one pads from the start of the menstrual cycle were applied to all 20 women
on day two they were given a pad from the second day of the cycle anf so on
found that 68% of women experienced changes to their cycle which brought them closer to the cycle of the odour donor
infradian rhythms - seasonal affective disorder
depressive disorder which has a seasonal pattern of onset
described and diagnosed as a mental disorder in DSM-5
main symptoms are persistent low mood alongside a general lack of activity and interest in life
often triggered during the winter months when the number of daylight hours are shorter
SAD is a particular type of infradian rhythm called circannual rhythm as it is subject to a yearly cycle
can also be classed as a circadian rhythm as the experience of SAD may be due to the disruption of the sleep/wake cycle and this can be attributed to prolonged period of daily darkness during winter
psychologists have hypothesised that the hormone melatonin is implicated in the cause of SAD
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 in the brain
chemical that has been linked to the onset of depressive symptoms
strength
evolutionary basis
strength on the menstrual synchrony research is that it may be explained by natural selection
synchronisation of the menstrual cycle is thought by some to have evolutionary value
for our distant 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 breast milk
improving their chances of survival
suggest that synchronisation is an adaptive strategy
limitation
methodological limitation
limitation of synchronisation studies is their methodological shortcomings
many factors that may effect change to the menstrual cycle including stress changes in diet excerisise etc
may act as a confounding variables which means that any supposed pattern of synchronisation is no more than would have been expected to occur by chance
may explain why some other studies eg Trevanthan et al have failed to replicate the findings
suggests that menstrual synchrony studieds are flawed
ultradian rhythms
stages of sleep - the sleep cycle
psychologists have identified five distinct stages of sleep that altogether span approximately 90 minutes
continues through the course of the night
each of the stages are characterised by a different level of brainwave activity which can be monitored using an EEG
stages 1 and 2
light sleep - person may be easily woken
stage 1 - the brain waves are high frequency and have a short amplitude - alpha waves
stage 2 - alpha waves continue but there are occasional random changes in pattern called sleep spindles
stages 3 and 4
known as deep sleep or slow wave sleep
brain waves are delta waves with lower frequency and higher amplitude
difficult to wake someone up at this point
stage 5 (REM sleep)
body is paralysed yet brain activity closely resembles the awake brain
brai produces theta waves
eyes occasionally move around
dreams are most often experienced during REM sleep but may also occur in deep sleep
strength
improved understanding
strength of research into ultradian rhythms is that it has improved understanding of age-related changes in sleep
sleep scientists have observed that SWS reduces with age
growth hormone is mostly produced during SWS therefore this is reduced in older people
according to eve van Cauter et al the resulting sleep deficit may explain various issues in old age such as reduced altertness
in order to increase SWS relaxation and medication may be used
suggest that knowledge of ultradian rhythms has practical value
limitation
individual differences
limitation of ultradian rhythms research is that there is significant variation between people
Tucker et al found large differences between participants in terms of the duration of each sleep stage
particularly stages 3 and 4
tucker et al suggest that these differences are liekly to be biologically determined
makes it doffult to describe normal sleep in any meaningful way
