infradian and ultradian rhythms Flashcards
What is an infradian rhythm?
Less than one cycle per 24 hours
Menstruation
SAD
What is the menstrual cycle?
Monthly changes in hormone levels regulate ovulation
28 days
Rising oestrogen causes ovary to develop egg and release it
Progesterone helps womb lining to grow thicker
Egg absorbed and womb lining leaves
Describe Stern and McClintock’s research
29 women with history of irregular periods
Pheromones gathered from 9 via cotton pad in armpit
Pads rubbed on lip of other pps
Day 1 - pads from start of cycle
Day 2 - second day of cycle etc
68% experienced changes to cycle
What is SAD?
Circannual rhythm - yearly cycle
Circadian - disruption to sleep/wake cycle - prolonged periods of darkness
How is melatonin implicated in SAD?
Pineal gland secretes melatonin until dawn (daylight)
Lack of light in morning in winter - secretion process continues for longer
Affects production of serotonin
What is an ultradian rhythm?
More than one cycle per 24 hours
Sleep cycle
What is the sleep cycle?
5 stages across 90 mins
Each stage characterised by levels of brainwave activity
What are stages 1 and 2 of the sleep cycle?
Light sleep - easily woken
Beginning of sleep - brainwave patterns become slower and more rhythmic - ALPHA waves
Deeper - becomes slower - THETA waves
What are stages 3 and 4 of the sleep cycle?
DELTA waves - even slower and have greater amplitude
Deep or slow wave sleep
Difficult to be woken
What is stage 5 of sleep?
REM sleep
Body is paralysed
Brain activity speeds up resembling awake brain
Correlation with dreams
Evaluation - evolutionary basis of menstrual cycle
Menstrual synchrony has evolutionary value
Newborns cared for collectively in a group - increased chance of survival
Schank - this would produce competition for highest quality male
Avoidance of synchrony would therefore be most adaptive
Evaluation - methodological limitations in synchronisation studies
Many confounding variables - stress, diet McClintock’s results by chance Small samples and relies on self report Other studies (Trevathan) found no evidence
Evaluation - evidence supporting stages of sleep
Dement and Kleitman - monitored sleep patterns in lab using EEG
Controlled for effects of caffeine
REM correlated with dreaming - awoken in this period = recollection
Replications found similar findings
Evaluation - animal studies
Knowledge of pheromones derived from animal studies
Sea urchins release pheromones
Speculative and inconclusive for humans
Evaluation - practical application of SAD
Phototherapy treatment Lightbox simulates strong light in morning and evening Resets melatonin levels Relieves symptoms in 60% Placebo effect of 30%
