Infradian & Ultradian Rhythms

• What is an infradian rhythm?

  A biological rhythm with less than 24-hour frequency
• What does the menstrual cycle regulate?

  Ovulation through monthly hormone changes
• What does the menstrual cycle refer to?

  The time between the first day of a woman's period
• What happens to oestrogen levels during the menstrual cycle?

  They rise, causing ovulation
• What role does progesterone play after ovulation?

  It helps thicken the womb lining for pregnancy
• What was the aim of Stern & McClintock's study?

  To investigate menstrual cycle synchronisation via pheromones
• How many women participated in Stern & McClintock's study?

  29 women with irregular periods
• What was done with the pheromone samples in the study?

  They were rubbed on the upper lips of participants
• What was the result for women on day 1 of the study?

  Pads from the start of the cycle were applied
• What percentage of women experienced cycle changes in the study?

  68% experienced changes closer to the donor's cycle
• What does SAD stand for?

  Seasonal Affective Disorder
• How is SAD classified in terms of biological rhythms?

  As an infradian rhythm and a circadian rhythm
• When are SAD symptoms typically triggered?

  During the winter months with shorter daylight
• What hormone is implicated in the cause of SAD?

  Melatonin
• What does the pineal gland secrete until dawn?

  Melatonin
• How does winter affect melatonin secretion?

  Melatonin secretion is increased
• What is the knock-on effect of increased melatonin?

  It affects serotonin levels in the brain
• What is the evolutionary basis for menstrual synchronisation?

  It may have provided advantages for offspring survival
• What are methodological limitations in menstrual synchrony studies?

  Confounding variables may affect menstrual cycle changes
• What do other studies suggest about menstrual synchrony?

  They fail to replicate supposed patterns of synchronisation
• What is an ultradian rhythm?

  A biological rhythm with more than one cycle in 24 hours
• How many stages of sleep are identified in ultradian rhythms?

  Five stages of sleep
• What is the duration of each sleep stage?

  They span 90 minutes throughout the night
• What characterizes stages 1 and 2 of sleep?

  Light sleep where the person can be easily woken
• What brain waves are produced in stage 1 of sleep?

  Alpha waves
• What happens to brain waves in stage 2 of sleep?

  Alpha waves continue with random changes
• What characterizes stages 3 and 4 of sleep?

  Deep sleep with delta waves produced
• What occurs during REM sleep?

  The body is paralysed, brain activity resembles wakefulness
• What brain waves are produced during REM sleep?

  Theta waves
• When are dreams most often experienced?

  During REM sleep
• What are the stages of sleep in ultradian rhythms?

  1. Stage 1: Light sleep, alpha waves
  2. Stage 2: Light sleep, alpha waves with changes
  3. Stage 3: Deep sleep, delta waves
  4. Stage 4: Deep sleep, delta waves
  5. REM Sleep: Paralysed body, theta waves, dreaming
• What are the implications of understanding ultradian rhythms?

  • Stage 3 & 4 sleep reduces with age
  • Growth hormone is produced during deep sleep
  • Knowledge has practical value for health
• What did Tucker et al (2007) find about sleep stages?

  Large differences in duration of sleep stages
• What does Tucker et al suggest about sleep stage differences?

  They are likely biologically determined
• What challenges arise from individual differences in sleep stages?

  • Difficult to define normal sleep
  • Variability complicates sleep research
• What is a strength for Infradian Rhythms?

  • Evolutionary Basis
  • Synchronisation of the menstrual cycle is thought by some to have evolutionary value
  • For our distant ancestors, it may have been advantageous for women to menstruate together and become pregnant at the same time, as babies who lose their mother would have access to breastmilk
  • This suggests that synchronisation is an adaptive strategy
• What is a limitation for Infradian Rhythms?

  • Methodological Limitations
  • There are many factors that may affect change to the menstrual cycle, which may act as confounding variables
  • This means that any supposed pattern of synchronisation is no more than would have been expected to occur by chance, proven by other studies failing to replicate it
  • This suggests that menstrual synchrony studies are flawed
• What is a strength for Ultradian Rhythms?

  • Improved Understanding
  • Sleep scientists have been observed that stage 3 & 4 reduces with age
  • Growth hormone is mostly produced during deep sleep, therefore this is reduced in older people
  • This suggests that knowledge of ultradian rhythms have practical value
• What is a limitation for Ultradian Rhythms?

  • Individual Differences
  • Tucker et al (2007) found large differences between participants in terms of duration of each sleep stage, particularly stage 3 & 4
  • Tucker et al suggests that these differences are likely to be biologically determined
  • This makes it difficult to describe normal sleep in any meaningful way