Infradian and Ultradian Rhythms Flashcards
What are infradian rhythms
they have less than one cycle in 24 hours
examples include the menstrual cycle and seasonal affective disorder
Describe the menstrual cycle as an infradian rhythm
includes ovulation, thickening of womb lining and losing the womb lining during menstruation
these changes are regulated by hormones oestrogen (pre ovulation) and progesterone (post ovulation)
the levels of these hormones act as endogenous pacemakers, acting as an internal body clock for the menstrual cycle
Discuss research into infradian rhythms and menstrual cycles
Stern and McClintock
samples of pheromones were gathered from 9 different women at different stages of their menstrual cycle, via a cotton pad placed on their armpit
pads were frozen and given to other Pp to rub on their top lip
found 68% of women experiences changes to their cycle which brought them closer to the cycle of their ‘odour donor’
suggest the synchronisation of periods is due to the presence of pheromones acting as exogenous zeitgebers (an external cue for the timing of an infradian rhythm)
What is a strength of infradian rhythms
evolutionary basis
menstrual synchrony may be explained by natural selection;
it may have been an advantage for women to menstruate and become pregnant at the same time so socially babies who had lost their mothers have access to breast milk and therefore improve their chances of survival
suggests synchronisation is an adaptive strategy
What is a limitation of infradian rhythms
limitation of synchronisation studies is their methodological shortcomings
confounding variables such as stress and diet effects the menstrual cycle meaning any supposed pattern of synchrony may be due to chance
may explain why studies have failed to replicate findings
suggesting menstrual synchrony studies are flawed
What are ultradian rhythms
type of biological rhythm
frequency of more than one cycle in 24 hours such as the stages of sleep
What is the sleep cycle
five distinct stages of sleep
each stage is characterised by a different level of brainwave activity which can be monitored using an EEG
Describe stage 1+2 of the sleep cycle
person can easily be woken
stage 1 - brain waves are alpha and are high freq and short amplitude
stage 2 - alpha waves continue but occasional random changes in pattern called sleep spindles
describe stage 3+4 of the sleep cycle
deep sleep/slow-wave sleep
brain waves are delta
lower freq and higher amplitude
difficult to wake one up
describe stage 5 of the sleep cycle
REM sleep
body is paralysed but brain activity closely resembles awake brain
theta waves and eyes occasionally move (hence Rapid Eye Movement)
dreams often occur
What is a strength of ultradian rhythms
improved understanding of age related changes in sleep
scientists observed that slow wave sleep reduces with age
this resulting sleep deficit may explain various issues in old age such as reduced alertness
suggest knowledge of ultradian rhythms has practical value
What is a limitation of ultradian rhythms
individual differences
there is significant variation between people (Tucker et al) found large differences between people in terms of the duration of each sleep stage, suggest that these are due to biological differences
makes it difficult to describe normal sleep in a meaningful way
Discuss research into ultradian rhythms
Dermot and Kleitman
EEG recordings made of 33 Pp over a nights sleep
brain waves followed a cyclic pattern of activation with relaxation occurring during SWS and rapid eye movements during high activation
9 Pp woken at different stages in their sleep cycle reported dreaming more frequently when woken in the REM stage
