Infradian and Ultradian

• What is an infradian rhythm?

  a type of biological rhythm with a duration of over 24 hours e.g. menstrual cycle
• What is an ultradian rhythm?

  a type of biological rhythm that lasts less than 24 hours (more than one cycle in 24 hours), e.g. stages of sleep
• What study supports the idea that the menstrual cycle is an infradian rhythm?

  • STERN AND MCCLINTOCK (1998)
  • 29 women with irregular periods
  • Samples of pheromones were gathered from 9 women at different stages of their menstrual cycles via a cotton pad under their armpit (worn for 8 hours).
  • Pads were treated with alcohol, frozen and rubbed onto the upper lip of the other 20 ppts
  • On day 1, pads from the start of the menstrual cycle were applied to all 20 women, day 2 they were given a pad from the second day of the cycle etc.
• Stern and McClintock findings?

  • 68% of women experienced changes to their menstrual cycle which brough them close to the cycle of their ‘odour donor’
• What is SAD and how is it an infradian rhythm?

  • A depressive disorder which has a seasonal pattern of onset
  • symptoms are triggered during the winter months when daylight hours decrease
  • A type of infradian rhythm called circannual rhythm as its subject to a yearly cycle
  • Can also be classed as a circadian rhythm as SAD may be due to the disruption of the sleep/wake cycle
  • Psychologists have hypothesised that the hormone melatonin is implicated in the cause of SAD.
• What is an example of an ultradian rhythm?

  • The sleep cycle
  • Psychologists have identified 5 distinct stages of sleep that altogether span approximately 90 minutes.
  • Each of these stages is characterised by a different level of brainwave activity which can be monitored using an EEG.
• Stage 1 and 2 of the sleep cycle?

  • ‘sleep escalator’
  • light sleep where the person may easily be woken
  • Brainwave patterns start to become slower and more rhythmic (alpha waves)
  • becoming even slower as sleep becomes deeper (theta waves)
• Stages 3 and 4 of the sleep cycle?

  • Involves delta waves which are slower and have a greater amplitude than earlier wave patterns
  • deep sleep or slow wave sleep, difficult to wake from
• What is Stage 5 (REM sleep) of the sleep cycle?

  • Body is paralysed yet brain activity speeds up, resembling the awake brain
  • REM (rapid eye movement) to denote fast, jerky activity of the eyes under the eyelids
  • REM activity during sleep is highly correlated with the experience of dreaming
• Research support for sleep cycle as an ultradian rhythm?

  • WILLIAM DEMENT AND NATHANIEL KLEITMAN (1957)
  • Monitored sleep patterns of 9 adults in a sleep lab
  • Activity was recorded on an EEG
  • Researchers controlled for the effects of caffeine and alcohol.
• Dement and Kleitman findings?

  • REM activity during sleep was highly correlated with the experience of dreaming
  • brain activity varied according to how vivid dreams were
  • ppts woken during dreaming reported very accurate recall of their dreams
  • Replications of this investigation have noted similar findings
  • Suggests evidence to support the idea of distinct stages in sleep and REM sleep is an important component of the ultradian sleep cycle
• Strength of the menstrual cycle being classed as infradian- evolutionary basis (AO3)

  • May have been advantageous for females to menstruate together and therefore fall pregnant around the same time
  • New-borns could be cared for collectively within a social group, increasing the chances of the offspring’s survival
  • Supports this classification by emphasizing the social and biological significance of a rhythm that extends beyond the daily timeframe
• Limitation of the biological basis of menstrual cycle?

  • The validity of the evolutionary perspective has been question
  • JEFFERT SCHANK (2004) has argued that if there were too many females cycling together within a social group, this would produce competition for the highest quality males
  • (thereby lowering the fitness of any potential offspring).
  • From this POV the avoidance of synchrony would appear to be most adaptive evolutionary strategy and therefore naturally selected.
• Limitations of methodology in Stern and McClintock (AO3)

  • Confounding variables: many factors that may affect the woman’s menstrual cycle (e.g. stress, changes in diet, exercise)
  • This means that any pattern of synchronisation identified, is no more than would have been expected to occur by chance
  • Research typically involves small samples of women and relies on ppts self-reporting the onset of their own cycle -> questions the validity of reporting and findings
  • other studies have failed to find any evidence of menstrual synchrony in all-female samples (e.g. TREVATHAN ET AL 1993)
• Strength of real life application to treat SAD (AO3)

  • One of the most effective treatments for SAD is phototherapy
  • This is a lightbox that simulates very strong light in the morning and evening. It is thought to reset melatonin levels in people with SAD.
  • This relieves the symptoms in up to 60% of sufferers.
• LIMITATION ULTRADIAN (AO3)

  • The problem with studying sleep cycles is the differences observed in people, which make investigating patterns difficult.
  • Tucker et al. (2007) found significant differences between participants in terms of the duration of each stage, particularly stages 3 and 4 (just before REM sleep)
  • This demonstrates that there may be innate individual differences in ultradian rhythms, which means that it is worth focusing on these differences during investigations into sleep cycles
  • Therefore we cannot conclude that this is entirely universal, endogenous/exogenous influences may affect stages