infradian and ultradian rhythms

• infradian rhythm - 


  type of biological rhythm with a frequency of less than one cycle in 24 hours

  eg menstruation and SAD
• the menstrual cycle -

  • infradian rhythm
  • governed by monthly changes in hormone levels which regulate ovulation
  • cycle is between first day of period when womb lining is shed to day before next period - takes approximately 28 days
  • rising oestrogen levels cause ovulation - after progesterone helps womb lining grow thicker readying womb for pregnancy - if no pregnancy egg is absorbed into body and menstrual flow occurs
• synchronising the menstrual cycle -

  • endogenous system - influenced by exogenous factors eg cycles of other women
  • Sturn and McClintock (1998) 29 women with history of irregular periods - samples of pheromones gathered from 9 women at different stages of their menstrual cycle with pads placed in armpits - rubbed on upper lip of other participants
  • pads of pheromones taken from each day of cycle were placed on corresponding day of 20 women's actual cycle - found 68% had changes to cycle bringing them closer to cycle of odour donor
• seasonal affective disorder -

  • seasonal pattern of onset and is a mental disorder in DSM-5
  • triggered during winter months when daylight hours become shorter
  • type of infradian rhythm called circannual rhythm (yearly cycle) -also circadian rhythm - disruption of sleep/wake cycle
  • melatonin implicated in cause of SAD - during night pineal gland secretes melatonin until dawn when there's increase in light - during winter lack of light in morn means secretion process continues for longer - knock on effect on production of serotonin in brain - chemical linked to onset of depressive symptoms
• ultradian rhythm - 


  type of biological rhythm with a frequency of more than one cycle in 24hrs

  such as stages of sleep
• stages of sleep -

  • 5 distinct stages that altogether span 90 mins approx - each characterised by different level of brainwave activity, monitored using EEG
  • stage 1 + 2 - light sleep - stage 1 is alpha waves with high freq and short amplitude - stage 2 alpha waves continue with occasional random changes
  • stage 3 + 4 - deep sleep or slow wave sleep (SWS) - delta waves with lower freq and higher amplitude
  • stage 5 (REM sleep) - body paralysed yet brain activity closely resembles awake brain - theta waves, rapid eye movement (REM) - dreams
• evaluation of infradian rhythms: evolutionary basis (strength) -

  • P: menstrual synchrony research may be explained by natural selection
  • E: evolutionary value - for distant ancestors it may have been advantageous for women to menstruate together and become pregnant at same time - in social groups this would allow babies who had lost mothers during or after birth to have access to breast milk improving chances of survival
  • L: suggest synchronisation is an adaptive strategy
• evolution of infradian rhythms: methodological limitations (limitation) -

  • P: methodological shortcomings
  • E: factors that may effect change to menstrual cycle (stress, diet, exercise etc) - act as confounding variables - means supposed pattern of synchronisation is no more than expected by chance
  • explains why other studies (Trevathan et al 1993) have failed to replicate findings
  • L: suggests menstrual synchrony studies are flawed
• evolution of ultradian rhythms: improved understanding (strength) -

  • P: improved understanding of age-related changes in sleep
  • E: sleep scientists observed that SWS reduced with age - growth hormone mostly produced during SWS therefore reduced in older people
  • E: Cauter et al (2000) resulting sleep deficit may explain various issues in old age such as reduced alertness - in order to increase SWS relaxation and medication may be used
  • L: suggests knowledge of ultradian rhythms has practical value
• evolution of ultradian rhythms: individual differences (limitation) -

  • P: significant variation between people
  • E: Tucker et al (2007) found large differences between participants in terms of duration of each sleep stage - particularly stage 3 and 4 - suggests these differences are likely to be biologically determined
  • L: makes it difficult to describe normal sleep in any meaningful way