Ultradian and Infradian Rhythms

• What is the definition of an ultradian rhythm?

  It lasts less than one day.
• Can you give an example of ultradian rhythms?

  Levels of alertness and cycles of brain activity during sleep.
• How do ultradian rhythms relate to human sleep patterns?

  • Sleep/wake cycle is a circadian rhythm.
  • Individual sleep stages are ultradian rhythms.
• What characterizes Stage 1 of human sleep?

  Light sleep with a decline in heart rate and relaxation of muscles, lasting approximately 15 minutes.
• What brain activity is observed during Stage 1 of sleep?

  Theta waves appear.
• How long does Stage 2 of sleep last?

  Approximately 20 minutes.
• What occurs during Stage 2 of sleep?

  Deeper sleep with noticeable bursts of sleep spindles and slower, larger theta waves.
• What is the primary characteristic of Stage 3 sleep?

  It is increasingly deep sleep with long slow delta waves.
• How difficult is it to wake someone from Stage 3 sleep?

  It is quite difficult to be woken from this stage.
• What happens during Stage 4 of sleep?

  It is deep sleep with a low metabolic rate and the release of growth hormones.
• What may occur during Stage 4 of sleep?

  Sleepwalking may occur.
• What characterizes REM sleep?

  Noticeable eye movements and dreaming occur, with increased brain oxygen and glucose demands.
• How does the cycle of sleep stages progress?

  It goes back through stages 2-4 after REM sleep.
• How often does the sleep cycle repeat?

  Every 90 minutes.
• How many full sleep cycles can a person experience in one night?

  A person can experience up to 5 full cycles in one night.
• Ultradian Rhythms AO3 - Individual differences


  • Tucker et al found significant differences between participants in terms of the duration of each stage, particularly stages 3 and 4
  • Demonstrates that there may be innate individual differences in UR
  • Study was carried out in a controlled lab setting, which meant that the differences in the sleep patterns could only be attributed to biological differences
  • While this study provide convincing support for the role of innate biological factors and ultradian rhythms, psychologists should examine other situational factors that may also play a role
• Ultradian Rhythms AO3 - Low ecological validity 


  • Way in which such research is conducted may tell us little about ultradian rhythms in humans
  • When investigating sleep patterns, participants must be subjected to a specific level of control and be attached to monitors that measure such rhythms
  • This may be invasive for the participant, leading them to sleep in a way that does not represent their ordinary sleep cycle
  • This makes investigating ultradian rhythms, such as the sleep cycle, extremely difficult as their lack of ecological validity ****could lead to false conclusions being drawn.
• Ultradian Rhythms AO3 - Case study


  • Randy Gardener remained awake for 264 hours
  • While he experienced numerous problems such as blurred vision and disorganised speech, he coped rather well with the massive sleep loss
  • After, Randy slept for just 15 hours and over several nights he recovered only 25% of his lost sleep
  • Interestingly, he recovered 70% of Stage 4 sleep, 50% of his REM sleep, and very little of the other stages
  • These results highlight the large degree of flexibility in terms of the different stages within the sleep cycle and the variable nature of this ultradian rhythm.
• What are infradian rhythms?

  Rhythms that last longer than 24 hours, such as weekly or monthly cycles
• Give an example of an infradian rhythm.

  The menstrual cycle
• What regulates the female menstrual cycle?

  • Hormones that promote ovulation
  • Hormones that stimulate the uterus for fertilization
• When does ovulation occur in the menstrual cycle?

  Roughly halfway through the cycle
• What hormone levels are highest during ovulation?

  Oestrogen levels
• How long does ovulation usually last?

  16-32 hours
• What happens to progesterone levels after the ovulatory phase?

  Progesterone levels increase in preparation for possible implantation
• What is the usual length of the menstrual cycle?

  Around 28 days
• What is the range of menstrual cycle lengths some women experience?

  From 23 days to 36 days
• What is seasonal affective disorder (SAD)?

  A condition where some people become depressed in the winter
• How is SAD classified in terms of biological rhythms?

  As an infradian rhythm governed by a yearly cycle
• What role does melatonin play in SAD?

  Melatonin, secreted by the pineal gland, is partly responsible for depressive symptoms
• What causes the increased secretion of melatonin during winter months?

  The lack of light during winter results in longer melatonin secretion
• How is the secretion of melatonin linked to depressive symptoms in SAD?

  Longer periods of melatonin secretion are linked to depressive symptoms
• Infradian rhythms AO3 - Effect of EZ

  • Research suggests that the menstrual cycle is, to some extent, governed by exogenous zeitgebers (external factors)
  • Reinberg examined a woman who spent three months in a cave with only a small lamp to provide light
  • Reinberg noted that her menstrual cycle shortened from the usual 28 days to 25 days
  • This result suggests that the lack of light (an exogenous zeitgeber) in the cave affected her menstrual cycle, and therefore this demonstrates the effect of external factors on infradian rhythms.
• Infradian rhythms AO3 - Further evidence of EZ


  • Russell et al. found that female menstrual cycles became synchronised with other females through odour exposure
  • Sweat samples from one group of women were rubbed onto the upper lip of another group + their menstrual cycles synchronised
  • Suggests that the synchronisation of menstrual cycles can be affected by pheromones, which have an effect on people nearby rather than on the person producing them
  • This indicates that external factors must be taken into consideration when investigating IR and that a more holistic approach should be taken
• Infradian rhythms AO3 - Evidence support for melatonin in SAD


  • Terman found that the rate of SAD is more common in Northern countries where the winter nights are longer
  • For example, Terman found that SAD affects roughly 10% of people living in New Hampshire (a northern part of the US) and only 2% of residents in southern Florida
  • These results suggest that SAD is in part affected by light (exogenous zeitgeber) that results in increased levels of melatonin.