biological rhythms - infradian and ultradian rhythms Flashcards
infradian rhythms - the menstrual cycle
- governed by monthly changes in hormone levels which regulate ovulation, hypothalamus
- typical cycle takes about 28 days
- rising levels of oestrogen cause ovary to develop and release an egg
- after this, progesterone thickens the womb lining, readying the womb for pregnancy
- if pregnancy does not occur, the egg is absorbed into the body, the womb lining comes away and leaves the body (menstrual flow)
- day 1 of the cycle is the first day of bleeding
infradian rhythms - synchronising the menstrual cycle
- the menstrual cycle is an endogenous system, but research suggests it may be influenced by exogenous factors, such as the cycles of other women
Stern and McClintock study -
- 29 women with irregular periods
- collected pheromones from 9 of them at different stages in period, via a cotton pad in their armpit
- pads worn for at least 8 hours then treated with alcohol and frozen, to then be rubbed on the upper lip of other participants
- on day one, pads from the start of the cycle were applied, on day two pads from day two of the cycle, etc.
- found that 68% of women experienced changes to their cycle that brought them closer to the cycle of their ‘odour donor’
- pheromones entrained menstrual cycle, women became more synchronised
infradian rhythms - seasonal affective disorder
- depressive disorder that has seasonal pattern of onset
- main symptoms are persistent low mood, lack of activity and interest in life
- symptoms triggered in winter months when number of daylight hours is shorter
- SAD is a circannual rhythm as it is subject to a yearly cycle
- also classed as a circadian rhythm because it may also be due to disruption of the sleep/wake cycle
- hypothesised that melatonin is implicated in SAD
- at night, the pineal gland secretes melatonin until dawn
- during winter there is less light in the morning, meaning the secretion happens for longer
- this is thought to have a knock-on effect on production of serotonin in the brain, a chemical linked to the onset of depressive symptoms
ultradian rhythms - stages of sleep
- each cycle last about 90 minutes, repeats throughout the night
- EEGs used for brain activity
- EOGs used for eye movement
- pons stops neuronal activity from entering body (paralysis in REM)
ultradian rhythms - stages 1 and 2
- light sleep where a person may be easily woken
- brain waves are high frequency and have a short amplitude (alpha waves)
- in stage 2, these continue but there are occasional changes in pattern called sleep spindles
ultradian rhythms - stages 3 and 4
- known as deep sleep or slow wave sleep (SWS)
- brain waves are delta waves with lower frequency and higher amplitude
- difficult to wake someone at this point
- growth hormone being produced
- cerebrospinal fluid flushed through brain
ultradian rhythms - stage 5 (REM sleep)
- body is paralysed yet brain activity closely resembles that of the awake brain
- brain produces theta waves and the eyes occasionally move around (rapid eye movement)
- dreams most often occur in REM sleep but can also happen in deep sleep
- pons stops brain activity from travelling to spinal cord (paralysis)
evaluation strength of menstrual synchrony research - evolutionary basis
- may be explained by natural selection
- synchronisation of the menstrual cycle is thought to have evolutionary value
- for our ancestors it may have been useful 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 to have access to breastmilk, therefore increasing chances of survival
evaluation limitation of menstrual synchrony research - methodological limitations
- 32% did not synchronise, suggests individual differences
- there are many factors that may effect change to the menstrual cycle, such as stress, diet and exercise
- these may act as confounding variables, meaning that any supposed pattern of synchronisation is no more than would have been expected to occur by chance
- this may explain why other studies have failed to replicate the findings
- decreased internal validity and reliability
evaluation strength of SAD - treatment
- LED light boxes can reduce symptoms of SAD
- replicate natural light, used in the morning to stop production of melatonin and start production of serotonin
- works for about 80% of sufferers
- beneficial for economy
- favoured over anti-depressants, drugs can take months to start working and do not always work
evaluation strength of research into ultradian rhythms - improved understanding
- sleep scientists have observed that SWS reduces with age
- growth hormone is mostly produced during SWS, therefore this is reduced in older people
- Eve van Cauter said that the resulting sleep deficit may explain issues in old age, such as reduced alertness
- in order to increase SWS, relaxation and medication may be used
- knowledge of ultradian rhythms has practical value
evaluation limitation of research into ultradian rhythms - individual differences
- Adrienne Tucker found large differences between participants in terms of duration of each sleep stage, particularly stages 3 and 4
- it is suggested that these differences are biologically determined
- this makes it difficult to describe ‘normal sleep’ in any way
evaluation strength of research into ultradian rhythms - Dement and Kleitman
- first researchers to use EEG to measure sleep and identify stages
-paved the way for all future research into investigating sleep - first to validate existence of sleep stages and to develop a scientific method for measuring and comparing people
- practical application - people can use watches and apps to track sleep and find out best time to go to sleep in order to wake up at the end of a cycle
