biological rhythms - infradian & ultradian rhythms Flashcards
how long are infradian rhythms
over 24 hours
examples of infradian rhythms
eg. menstrual cycle, seasonal affective disorder
how is the menstrual cycle an example of an infradian rhythm
- governed by monthly hormone changes
- typical cycle is 28 days
- rising levels of oestrogen cause ovary to develop egg & release it (ovulation)
- after ovulation, progesterone helps womb lining thicken
research on synchronisation of menstrual cycle
mcclintock (1998) showed how menstrual cycles may synchronise due to pheromones
research of stern & mcclintock
- studied 29 women with history of irregular periods
- pheromone samples gathered from 9 women at different stages of cycle, by placing pad
under armpit (for at least 8 hours) - pads treated with alcohol & frozen, then rubbed on upper lip of other participants
- on day one, pads from day 1 of cycle given to 20 women & so on
- found 68% experienced changes to cycle (brought closer to ‘odour donor’)
how is seasonal affective disorder an example of an infradian rhythm
- main symptoms = persistent low mood & lack of activity/interest in life
- triggered in winter when number of daylight hours is shorter
- circannual rhythm (type of infradain rhythm) as yearly cycle
- hormone melatonin is implicated in cause of SAD
- during night time, the pineal gland secretes melatonin until dawn when an increase in light
- lack of light in morning during winter means secretion continues for longer
- knock-on effect on production of serotonin (linked to onset of depressive symptoms)
infradian rhythms: AO3 +) menstrual synchrony research may be explained by natural selection
E:
- synchronisation of menstrual cycle (researched by stern & mcclintock) has evolutionary value
- may have been advantageous for distant ancestors as women could menstruate & become pregnant at same time
- allow babies who’ve lost mothers during/after childbirth to have access to breastmilk = increase chance of survival
T: suggests synchronisation is an adaptive strategy
infradian rhythms: AO3 -) synchronisation studies have methodological limitations
E:
- many factors which could effect change to menstrual cycle (eg. stress, changes in diet, exercise) = confounding variables
- any supposed pattern of synchronisation may have occurred by chance
- may explain why other studies failed to replicate findings (eg. trevathan et al. 1993)
T: suggests menstrual synchrony studies are flawed
how long are ultradian rhythms
under 24 hours
example of ultradian rhythm
stages of sleep (sleep cycle)
how is the stages of sleep an example of an ultradian rhythm
- each stage characterised by different level of brainwave activity which can be monitored using EEG
- 5 distinct stages over around 90 minutes
- stages 1 & 2: light sleep
- stage 1 = brain waves are high frequency & short amplitude (alpha waves)
- stage 2 = alpha waves continue but occasional random pattern changes (sleep spindles) - stages 3 & 4: deep sleep/slow wave sleep (SWS)
- brain waves are delta waves = lower frequency & higher amplitude - stage 5 (REM): body paralysed but brain activity closely resembles awake brain
- brain produces theta waves
- eyes may move around
- dreams most often occur during REM sleep
ultradian rhythms: AO3 +) research has improved understanding of age-related changes in sleep
E:
- sleep scientists observed slow wave sleep (stages 3/4) reduces with age
- growth hormone mostly produced during slow wave sleep, so reduced in older people
- cauter et al. (2000) said the resulting sleep deficit may explain issues in older age (eg. reduced alertness)
T: suggests knowledge of ultradian rhythms has practical value
ultradian rhythms: AO3 -) significant difference between people
E:
- tucker et al. (2007) found large differences between participants regarding duration of sleep stages, especially stage 3 & 4
- suggested these differences likely to be biologically determined
T: difficult to describe ‘normal sleep’ in meaningful way
