Biological Rhythms: Infradian & Ultradian Rhythms Flashcards
Infradian Rhythms - Menstrual Cycle
Infradian Rhythms - Cycle lasts over 24 hrs, may be weekly, monthly, annually.
1) Human menstrual cycle is about 28 days (i.e. less than one cycle in 24 hours)
2) Rising levels of oestrogen cause ovary to release an egg (ovulation). Then progesterone helps the womb lining to thicken, readying the womb for pregnancy. If pregnancy does not occur, the egg is absorbed and the womb lining comes away (menstrual flow).
Exogenous Zeitgebers - Menstrual Cycle
Exogenous zeitgebers may synchronise menstrual cycles.
1) Stern and McClintock studied 29 women with irregular periods. Pheromones were taken from some at different stages of their cycles, via a cotton pad under their armpits. These pads were cleaned with alcohol and later rubbed on the upper lips of the other pps.
2) 68% of women experienced changes to their cycle which brought them closer to the cycle of their ‘odour donor’.
Strength of Infradian Rhythm
RESEARCH ON MENSTRUAL CYCLE SHOWS ITS EVOLUTIONARY BASIS
1) For distant ancestors it may have been advantageous for females to menstruate together and become pregnant at the same time.
2) In a social group, this would allow babies who had lost their mothers to have access to breast milk, thereby improving their chances of survival.
—> Suggests that synchronisation is an adaptive strategy.
Limitation of Infradian Rhythm
METHODOLOGY USED IN SYNCHRONISATION STUDIES
1) There are many factors that may change a woman’s menstrual cycle and act as confounding variables (e.g. stress, changes in diet, etc).
2) Any supposed pattern may occur by chance —> may be why other studies (e.g. Trevathan et al.) haven’t replicated Stern and McClintock’s original findings.
—> This suggests that menstrual synchrony studies are flawed.
Infradian Rhythms - SAD
1) Seasonal affective disorder (SAD) is a depressive disorder (low mood, lack of activity) with a seasonal pattern - circannual rhythm.
2) Often called the ‘winter blues’ because the symptoms are triggered during the winter months when the number of daylight hours becomes shorter.
SAD - Melatonin
SAD may be caused by the hormone melatonin.
1) During the night, the pineal gland secretes melatonin until dawn, when there is an increase in light.
2) In winter, less light means secretion goes on for longer —> has a knock-on effect on the production of serotonin in the brain (low serotonin is linked to depressive symptoms).
Ultradian Rhythms - Stages of Sleep
Ultradian Rhythms - More than 1 cycle in 24 hrs, cycle lasts less than 24 hrs.
1) Sleep pattern occurs in 90-minute periods (i.e. more than one cycle in 24 hrs).
2) Divided into 5 stages, each characterised by a different level of brainwave activity (monitored using EEG).
5 Stages of Sleep - Stages 1 & 2
1) Light sleep where a person may be easily woken.
2) In stage 1, brain waves are high frequency and have a short amplitude —> these are alpha waves.
3) In stage 2, the alpha waves continue but there are occasional random changes in pattern called sleep spindles.
4) At beginning of sleep, brainwave patterns are slow & rhythmic (alpha waves), & become slower as sleep gets deeper (theta waves).
5 Stages of Sleep - Stages 3 & 4
1) Deep sleep or slow wave sleep (SWS) —> the individual waves now have low frequency & higher amplitude.
2) It is difficult to wake someone at this point.
3) These stages involve even slower brain waves (delta waves).
5 Stages of Sleep - Stage 5
1) Stage 5 (REM sleep).
2) The body is paralysed yet brain activity closely resembles that of the awake brain.
3) During this time, the brain produces theta waves and the eyes occasionally move around, thus rapid eye movement (REM).
4) Dreams most often experienced during REM sleep, but may also occur in deep sleep.
Strength of Ultradian Rhythm
PRACTICAL VALUE - UNDERSTANDING AGE-RELATED CHANGES IN SLEEP
1) SWS reduces with age - Growth hormone is produced during SWS so this becomes deficient in older people.
2) van Cauter et al. suggest the reduced sleep may explain impairments in old age - SWS sleep can be improved using relaxation and medication.
—> Suggests that knowledge of ultradian rhythms has practical value.
Limitation of Ultradian Rhythm
INDIVIDUAL DIFFERENCES IN SLEEP STAGES
1) Tucker et al. found large differences between pps in the duration of stages 3 and 4.
2) Suggest that these differences are biologically determined.
—> Makes it difficult to describe ‘normal sleep’ in any meaningful way.
Extra Evaluation - Sleep Lab
STUDIES OF SLEEP IN LAB SETTING
1) One benefit of conducting studies of sleep in lab settings is control of extraneous variables, e.g. noise, temperature that may affect sleep.
2) BUT, lab studies involve pps being attached to complicated machinery - so their sleep doesn’t represent their ordinary sleep patterns.
3) Means it might be best to conduct some studies in ppl’s own homes and compare patterns with records made in lab settings.
