Biological Rhythms

• Biological Rhythms

  Repeated patterns of changes in the body that are regulated by an internal clock
• What are the 3 biological rhythm?

  1. Circadian
  2. Ultradian
  3. Infradian
• Infradian Rhythm


  A type of biological rhythm that takes longer than 24 hours to complete one cycle
• Give an example of an Infradian Rhythm

  Menstrual Cycle
• What is the Menstrual Cycle?


  The time from the first day of a womans period to the day before her next period. Average length is 28 days
• Menstrual Cycle Explained

  • First the levels of oestrogen rise which causes ovary to develop and release an egg and the lining of the uterus thickens
  • Levels of progesterone rise helping to maintain the lining of the womb ready for the embryo
• Synchronising menstrual cycle

  • Studied 29 PPs with a history of irregular periods
  • Samples of pheromones were gathered from 9 women at different stages of their cycle via a cotton pad that they wore on their armpit for 8 hours
  • The pad were frozen and treated with alcohol and were then rubbed on other PPs lips
  • Results found 68% of women experienced changes to their cycle
• What are pheromones?


  An odourless chemical substance that we release into the environment that affects the behaviour of others
• Seasonal Affective Disorder

  • A depressive disorder which has a seasonal pattern of onset and diagnosed as a mental disorder
  • Main symptoms are low mood with a lack of general activity and interest in life
  • Often occurs during winter months with less daylight
  • SAD is a particular type of infradian rhythm
• AO3 Infradian Rhythm: Evolutionary basis

  • Menstrual synchrony is that it may be explained by natural selection
  • For our distant ancestors it may have been advantageous for females to menstruate and become pregnant at the same time
  • In a social group it would allow babies who lost their mothers to have access to breast milk improving their chances of survival
  • Synchronisation is an adaptive strategy
• AO3 Infradian Rhythm: Methodological Limitations

  • Synchronisation studies have poor methodologies
  • There are many factors that may effect change in a womans menstrual cycle such as stress and changes in diet
  • These may act as confounding variables
  • This makes it hard to also replicate findings so menstrual synchrony studies are flawed
• AO3 Infradian Rhythm: Real World Application

  • There is effective treatment for SAD which is light therapy where a box stimulates very strong light to reset the bodys internal clock
  • Studies show this helps reduce effects in 80% of people and light therapy is preferred than antidepressants as it is more safe
  • However it can give headaches and eye strain
  • Relapse rates is double compare to those getting CBT
• Ultradian Rhythms


  Take less than a day and you can have more than one cycle in 24 hours
• Give an example of an ultradian rhythm

  Stages of sleep
• How do psychologists know about the different stages of sleep?

  EEGs
• Stage 1 of Sleep

  • Light sleep where a person may easily be woken up
  • Brain waves are high frequency and have a short amplitude
• Stage 2 of Sleep

  • The alpha waves continue but there are occasional random changes in pattern called sleep spindles
• Stage 3 and 4 of Sleep

  • Known as deep sleep
  • The brain waves are delta waves
  • It is difficult to wake someone at this point
• Stage 5 of Sleep

  • Also known as REM sleep
  • Body is paralysed yet brain activity closely resembles that of the awake brain
  • The brain produces theta waves and the eyes occasionally move around ( rapid eye movement)
  • Dreams often occur here
• AO3 Ultradian Rhythms: Improved Understanding

  • Improved understanding of age related changes in sleep
  • Deep sleep reduces with age and the growth hormone is mostly produced during this becomes deficient in old people
  • In order to increased deep sleep relaxation and medication can be used
  • Has practical value
• AO3 Ultradian Rhythms: Individual differences

  • Ultradian rhythms research has significant variation between people
  • There are large differences between PPs in terms of the duration of each stage of sleep
  • The differences are likely to be biologically determined
  • Makes it difficult to describe 'normal' sleep
• AO3 Ultradian Rhythms: Research Support

  • There were 9 PPs that could eat normally during the day and could have no caffeine or alcohol
  • Before they normally sleep they put on electrodes
  • When PPs were awoken during non REM sleep only 7% remembered their dreams
  • When woken during REM sleep around 80% remembered their dreams