Biological rhythms: Infradian & ultradian rhythms Flashcards
Menstrual cycle
Infradian rhythms
Governed by monthly changes in hormone levels which regulate ovulation
Cycle refers to time between first day of a woman’s period to the day before her next period
Typical cycle is 28 days
During each cycle, rising level of oestrogen cause ovary to develop an egg & release it
After ovulation, progesterone helps womb lining to grow thicker, readying womb for pregnancy
If pregnany does not occu, egg is absorbed into body and lining comes away & leaves the body
Synchronising the menstrual cycle
Infradian rhythms
Menstrual cycle is endogenous system that may be influenced by exogneous factors (i.e. cycles of other women)
Stern & McClintock studied 29 women w/ history of irregular periods
Sample of pheromones gathered from 9 of the women at diff stages of their cycle via cotton pad in their armpit
Pads worn for at least 8 hours then treated w/ alcohol & frozen, to be rubbed on the upper lip of other ppts
On day 1, pads from start of menstrual cycle applied to all 20 women
On day 2, pad from 2nd day of cyle & so on
Stern & McClintock found that 68% of women experienced changes to their cycle which brought the closer to cycle of ‘odour donor’
Seasonal affective disorder (SAD)
Infradian rhythms
Depressive disorder which has seasonal pattern of onset & is described & diagnosed as mental disorder in DSM-5
Main symptoms are persistent low mood & general lack of activity or interest in life
SAD often referred to as winter blues as symptoms are triggered during winter months
SAD is type of infradian rhythm called circannual rhythm
However, can be classed as circadian rhytgm as experience of SAD may be due to disruption of s/w cycle which can be caused by prolong periods of darkness in winter
Cause of SAD
Infradian rhythms
Psychologists hypothesised that melatonin is implicated in cause of SAD
During night, pineal gland secretes melatonin until dawn when there’s an increase in light
During winter, lack of light in morning means this secretion process continues for longer
This is thought to have knock-on effect on production of serotonin in brain - chemical linked to onset of depressive symptoms
Evaluation: Evolutionary basis
Infradian rhythms
Strength of menstrual synchrony: explained by nat selection
Synchronisation of mens cycle is thought to have evolutionary value
For our distant ancestors it may have been advantageous for women to menstrate & get pregnant together
In 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
Therefore, synchronisation may be an adaptive strategy
Evaluation: Methodological limitations
Infradian rhythms
Limit of synchronisation studies: methodological shortcomings
Many factors may effect change to mens cycle (i.e. stress, changes in diet, etc)
These may act as 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 other studies have failed to replicate the findings
Therefore, menstrual synchrony studies are flawed
Stages of sleep cycle
Ultradian rhythms
Psychologists have identified 5 stages that span around 90 mins - cycle that continues throughout the course of the night
Each stage is characterised by diff level of brainwave activity which can be monitored using EEG
Stages 1 & 2
Ultradian rhythms - sleep cycle
Light sleep where a person is easily woken
In stage 1, brain waves are high frequency & have short amplitude - alpha waves
In stage 2, alpha waves continue but there are occasional random changes in pattern called sleep spindles
Stages 3 & 4
Ultradian rhythms - sleep cycle
Deep sleep or slow wave sleep (SWS)
Brain waves are delta waves w/ lower frequency & higher amplitude
Difficult to wake someone at this point
Stage 5 (REM sleep)
Ultradian rhythms - sleep cycle
Body is paralysed yet brain activity closely resembles that of awake brain
During this time, brain produces theta waves & eyes occasionally move, thus rapid eye movement (REM)
Dreams are most often experienced during REM but may also occur in deep sleep
Evaluation: Improved understanding
Ultradian rhythms
Strength: research has improved understanding of age-related changes in sleep
Sleep scientists have observed that SWS reduces w/ sleep
Growth hormone mostly produced during SWS therefore this is reduced in older people
Van Cauter et al said resulting sleep deficit may explain various issues in old age such as reduced alertness
In order to increase SWS, relaxtion & medication may be used
Therefore, knowlegde of ultradian rhythms has practical value
Evaluation: Individual differences
Ultradian rhythms
Limit: significant variation between people
Tucker et al found large diffs between ppts in terms of duration of each sleep stage (particularly 3 & 4)
Tucker suggests that these diffs are likely to be biologically determined
Therefore, its difficult to describe ‘normal sleep’ in any meaningful way
