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
• Circadian Rhythms


  A biological rhythm that takes about 24 hours to complete a cycle
• Give an example of a circadian rhythm

  Sleep wake cycle
• Siffre's cave study

  • Spent several extended periods underground to study his biological rhythm
  • Deprived of natural light and sound
  • He once stayed there for 2 months thinking it had only been a month
  • He did it again for 6 months
  • His biological rhythm was around 25 hours and he had schedule of waking up and going to sleep
• Research on Circadian Rhythms

  • PPs spent 4 weeks in a WWII bunker deprived of natural light
  • All PPs displayed a cycle between 24 and 25 hours apart from one PP who had a cycle of 29 hours
• What did Siffre's cave study find?

  1. We have an internal biological clock that controls our circadian rhythm
  2. Our sleep wake cycle may be nearer to 25 hours
  3. We need exogenous zeitgebers to help regulate our sleep wake cycle
• AO3 Circadian Rhythms: Shift Work

  • Provides understanding of the consequences of a disrupted sleep wake cycle
  • Night workers experiences reduced concentration around 6 in the morning so more accidents happen
  • There is a relationship between shift work and poor health- 3 times more likely to get heart disease
  • Can help worker productivity
• AO3 Circadian Rhythm: Medical Treatment

  • Circadian rhythms coordinate a number of the body's basic processes such as heart rate and digestion
  • Medicine has been created to correspond to a person's biological rhythm
  • Aspirin treats heart attacks and better taken at night
  • Can help the effectiveness of drug treatment
• AO3 Circadian Rhythm: Individual Differences

  • Generalisations are difficult to make
  • The research studies had small samples and sleep wake cycles vary for different people
  • It is difficult to use research data based on other people
• 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
  • These are alpha waves
• 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 with lower frequency and higher amplitude
  • 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