infraidan rhythms

• Infradian Rhythms

  Biological rhythms that last longer than 24 hours, such as weekly, monthly or annually
• Ultradian Rhythms

  Biological rhythms that last less than 24 hours
• Types of Biological Rhythms

  • Infradian (>24 hours)
  • Circadian (24 hours)
  • Ultradian (<24 hours)
• Types of Exam Questions

  • Outline
  • Outline Examples
  • Outline Research
• Essay Writing & Evaluation

  Outline and evaluate infradian and/or ultradian rhythms (16 marks)
• The specification requires students to outline, provide examples of, and evaluate infradian and ultradian rhythms
• Examples of Infradian Rhythms

  • Female menstrual cycle
  • Seasonal affective disorder
  • Hibernation (in animals)
• Female Menstrual Cycle

  • Monthly infradian rhythm
  • Regulated by hormones (oestrogen and progesterone)
  • Ovulation occurs halfway through cycle when oestrogen levels are highest
  • Typical cycle is 28 days but can vary 23-36 days
• Lack of light (exogenous zeitgeber)

  Affected woman's menstrual cycle in a cave study, shortening it from 28 to 25.7 days
• Exposure to female sweat samples (pheromones as exogenous zeitgeber)

  Synchronised menstrual cycles of separate groups of women
• Examples of Ultradian Rhythms

  • Human sleep patterns
  • Meal patterns
• Human Sleep Patterns


  • Alternates between NREM (light and deep sleep) and REM (dream sleep) in 90 minute cycles
  • Up to 5 full cycles per night
• When providing an example of an ultradian rhythm, the cycle should be explicitly mentioned as occurring more than once every 24 hours
• Randy Gardener remained awake for 264 hours

  After this, he slept for just 15 hours and recovered 70% of Stage 4 sleep, 50% of REM sleep, but very little of other stages
• Tucker et al. found significant individual differences in the duration of sleep stages, particularly Stages 3 and 4
• Idiographic vs. nomothetic approaches, highly controlled laboratory research, and issues with ecological validity are also worth considering when evaluating ultradian/infradian rhythms
• Seasonal affective disorder (SAD)

  An infradian rhythm that is governed by a yearly cycle, where people experience a low mood (depression) in the winter months
• Research into ultradian/infradian rhythms has found results/conclusions
• Ultradian rhythm


  A biological rhythm with a cycle shorter than 24 hours
• Infradian rhythm

  A biological rhythm with a cycle longer than 24 hours
• The most important word in the question "Outline what research into ultradian/infradian rhythms has found" is "found", as it refers to the results or conclusions of the research
• Research into ultradian/infradian rhythms

  • Highly controlled laboratory research
  • Lack of ecological validity
• Lack of light (exogenous zeitgeber) in a cave

  Affected a woman's menstrual cycle, shortening it from 28 days to 25.7 days
• This result suggests that external factors can affect infradian rhythms
• Exposure to female odour

  Synchronised menstrual cycles between separate groups of women
• This suggests that the synchronisation of menstrual cycles can be affected by pheromones (external factors)
• A more holistic approach, as opposed to a reductionist approach, should be taken when investigating infradian rhythms to consider both endogenous and exogenous influences
• The problem with studying sleep cycles is the individual differences found in humans
• Tucker et al. found significant differences between participants in terms of the duration of each stage of sleep, particularly stages 3 and 4
• The highly controlled laboratory setting of the Tucker et al. study meant the differences in sleep patterns could not be attributed to situational factors, but only to biological differences between participants
• The way in which research on ultradian rhythms, such as sleep cycles, is conducted may tell us little about ultradian rhythms in humans due to the risk of false conclusions and low levels of ecological validity
• When investigating sleep patterns, participants must be subjected to a specific level of control and be attached to monitors, which may be invasive and lead them to sleep in a way that does not represent their ordinary sleep cycle