8. Infradian and Ultradian Rhythms

• Infradian Rhythms

  • A type of biological rhythm with a frequency of less than one cycle in 24 hours such as menstruation and seasonal affective disorder
• The menstrual cycle

  • Governed by monthly changes in hormone levels which regulate ovulation
  • 28 day typical cycle
  • Rising levels of oestrogen cause the ovary to develop an egg and release it (ovulation)
  • After this, progesterone helps the womb lining to grow thicker readying for pregnancy
  • If pregnancy does not occur, the egg is absorbed into the body and the womb lining leaves the body
• Synchronising the menstrual cycle

  • Endogenous system influenced by exogenous factors
  • Stern and McClintock study - pheromones are an exogenous factor that influence the menstrual cycle
  • 29 women with a history of irregular periods
  • Samples of pheromones gathered from nine of the women at different stages of cycle via a cotton pad placed under armpit - alcohol and frozen, rubbed on upper lip of other pps
  • Pads applied to all 20 women every day of cycle
  • 68% of women experienced changes to their cycle which brought them closer to 'odour donor' cycle
• Seasonal affective disorder

  • Depressive disorder with a seasonal pattern of onset and is described as a mental disorder in DSM-5
  • Low mood, lack of activity and interest in life
  • 'Winter blues'
  • Circannual rhythm as it is subject to a yearly cycle
  • Can be classed as circadian as SAD may be due to disruption of the sleep/wake cycle and can be attributed to long periods of darkness
  • At night, the pineal gland secretes melatonin until dawn where there is an increase in light
  • Lack of light in winter - more secretion
  • Decreases serotonin levels which is linked to depression
• AO3 of Infradian - Research Support

  • Reinberg examined a woman who spent three months in a cave with only a small lamp to provide light and found that her menstrual cycle shortened from 28 days to 25.7 days
  • Demonstrates the effect of external factors
  • Also supported by Stern and McClintock's study
  • Synchronised menstrual cycle and pregnancies has an evolutionary advantage as childcare can be shared among multiple mothers at the same time
  • Encourages a more holistic approach
• AO3 of Infradian - methodological issues

  • Findings in this area should be scrutinised eg. Stern and McClintock study
  • Many factors can influence the menstrual cycle eg. stress, changes in diet and excercise which act as confounding variables
  • As these factors are exogenous zeitgebers, they will each act on the entrainment of menstrual cycles which means that any supposed pattern of synchronisation is no more than would have been expected to occur by chance
  • May explain why it has been hard to replicate
• AO3 of Infradian - Real-world application

  • Treatment for SAD using light therapy, a box which simulates very strong light to reset the body's internal clock
  • Sanassi - this helps reduce the effects of SAD in about 80% of people
  • Preferred over antidepressants to treat SAD because it is regarded as safe
  • HOWEVER - use of light therapy is not without risks and side effects can range from headaches to eye strain
  • Rohan et al recorded a relapse rate of 46% over successive winters, compared to 27% in a comparison group receiving CBT
• Ultradian Rhythms

  • A type of biological rhythm with a frequency of more than one cycle in 24 hours such as the sleep cycle/stages of sleep
• Stages of Sleep

  • Span approx. 90 minutes
  • Characterised by brainwave activity monitored using an EEG
  • Stages 1 and 2 - light sleep, easily woken, high frequency, short amplitude (alpha waves), sleep spindles in stage 2
  • Stages 3 and 4 - slow wave sleep, delta waves w/ a low frequency and high amplitude, hard to wake up
  • Stage 5 - REM sleep, body is paralysed but brain activity resembles an wake brain, theta waves, dreams most likely experienced here
• AO3 of Ultradian - improved understanding

  • Age-related changes in sleep
  • Sleep scientists have observed that SWS reduces with age as growth hormone is mostly produced during SWS which is therefore reduced in older people
  • Older people will experience less deep sleep and Cauter et al. has suggested that the resulting sleep deficit may explain various issues in old age such as reduced alertness
  • Intervention is possible such as medication
  • Practical basis
• AO3 of Ultradian - individual differences

  • Significant variations observed in people
  • Tucker et al found large differences between pps in terms of the duration of each sleep stage, particularly stages 3 and 4, suggesting that these differences are likely to be biologically determined
  • Cannot generalise sleep is the same for everyone as it hinders treatments eg. hypersomnia and insomnia
  • Over simplistic conclusions may lack validity
• AO3 of Ultradian - sleep labs

  • Controls extraneous variables and can exclude situational factors such as noise that may affect sleep, in order to gain more insight into the biological differences between pps and their sleep patterns
  • HOWEVER lab studies involve being attached to complicated machinery, which may become invasive for pps
  • The cost of such high experimental control and accurate measurement is a loss in ecological validity. Sleep labs do not replicate the pps normal sleeping environment which can vary significantly from person to person