Biological rhythms: infradian and ultradian rhythms Flashcards
Infradian rhythms
└a type of biological rhythm with a frequency of less than one cycle in 24 hours
└e.g. menstruation, seasonal affective disorder (SAD)
Infradian rhythms
parts
The menstrual cycle
Research study
Seasonal affective disorder (SAD)
Infradian rhythms
The menstrual cycle
└example of an infradian rhythm
└controlled by monthly changes in hormone levels which regulate ovulation
└cycle is approximately 28 days
└oestrogen causes ovulation, then progesterone helps womb lining grow thicker to prepare for pregnancy. If there is no pregnancy, menstrual flow occurs
Infradian rhythms
Research study
└Kathleen Stern and Martha McClintock (1998)
└menstrual cycles may synchronise as a result of female pheromones
└29 women with irregular periods
└samples of pheromones gathered from 9 different women at different stages of their menstrual cycles via a cotton pad placed on their armpit for 8 hours
└pads treated with alcohol and frozen, then rubbed on the upper lip of other participants
└on day one, pads from the start of the menstrual cycle were applied, on day 2 they were given pads from the second day and so on
└68% of women had a closer cycle to their owner donor
Infradian rhythms
Seasonal affective disorder (SAD)
└depressive disorder with seasonal pattern of onset
└mental disorder in DSM-5
└symptoms: persistent low mood, lack of activity
└symptoms triggered in winter months when there is less daylight
└SAD is a particular type of infradian rhythm called circannual rhythm
└as is subject to a yearly cycle
└can also be classed as a circadian rhythm
└as may be due to the disruption of the sleep/wake cycle
└attributed to prolonged periods of darkness during winter
└suggested that the hormone melatonin causes SAD
└at night the pineal gland secretes melatonin until light is detected
└less light in morning= secretion for longer
└knock on effect if serotonin production
└linked to depressive symptoms
Ultradian rhythms
└a type of biological rhythm with a frequency of more than one cycle in 24 hours
└e.g. stages of sleep
Stages of sleep
└5 stages of sleep that span 90 minutes
└repeated throughout the night
└each stage characterised by different level of brainwave activity that can be monitored using EGG
Stages of sleep
Stages 1 and 2
└light sleep
└person easily woken
└alpha waves: brainwaves become slower and more rhythmic
└theta waves: then slower as sleep becomes deeper
Stages of sleep
Stages 3 and 4
└delta waves: slower waves, greater amplitude
└deep sleep/slow wave sleep
└person not easily woken
Stages of sleep
Stage 5, REM sleep
└body paralysed but brain activity speeds up
└resembles the awake brain
└REM= rapid eye movement
└highly correlated with dreaming
Stages of sleep
all stages
Stages 1 and 2
└light sleep
└person easily woken
└alpha waves: brainwaves become slower and more rhythmic
└theta waves: then slower as sleep becomes deeper
Stages 3 and 4
└delta waves: slower waves, greater amplitude
└deep sleep/slow wave sleep
└person not easily woken
Stage 5, REM sleep └body paralysed but brain activity speeds up └resembles the awake brain └REM= rapid eye movement └highly correlated with dreaming
Biological rhythms: infradian and ultradian rhythms
strengths
summary
Evidence supports the idea of distinct stages in sleep - William Dement and Nathaniel Kleitman (1957)
Practical application- SAD- Eastman et al (1998)
Animal studies
Biological rhythms: infradian and ultradian rhythms
strengths
Evidence supports the idea of distinct stages in sleep
└William Dement and Nathaniel Kleitman (1957)
└monitored the sleep patterns of 9 adult participants in a sleep lab
└brain activity was recorded on an EEG
└researchers controlled the effects of caffeine and alcohol
└REM activity during sleep was highly correlated with dreaming
└activity varied according to how vivid dreams were
└participants woken up during dreams had very accurate recall of dreams
└small sample size of original study= bad
└replications of study have similar findings
└study suggests REM (dream) sleep is an important component of the ultradian sleep cycle
Biological rhythms: infradian and ultradian rhythms
strengths
└one of the most effective treatments for SAD= phototherapy
└light box stimulates very strong light in the morning and evening
└is thought to reset melatonin levels
└Eastman et al (1998)
└relieves symptoms in up to 60% of sufferers
└sham negative-ion generator
└=placebo effect of 30%
└=reduces validity of the effect of chemical influence if phototherapy
Biological rhythms: infradian and ultradian rhythms
strengths
└many animal studies on the role of pheromones in animal sexual selection
└e.g. sea urchins release pheromones into surrounding water so other urchins in the colony will eject their sex cells simultaneously
└evidence on pheromones in humans limited and inconclusive
└animal studies can’t be generalised
