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
• Endogenous Pacemakers


  Internal body clocks that regulate our biological rhythms
• Exogenous Zeitgebers 


  External cues that influence and reset our internal biological clocks
• Suprachiasmatic nucleus (SCN)


  A tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain
• What does the SCN do?

  • It is an example of a endogenous pacemaker that sets the timing of when we need to sleep
  • The SCN regulates the pineal gland that releases melatonin which helps us sleep
• Animal Research and the SCN

  • In 30 chipmunks their SCN was destroyed and they were returned to their natural habitat for 80 days
  • At the end the chipmunks lost their sleep wake cycle and many were killed by predators
• Give an example of an endogenous pacemaker

  The SCN
• Give examples of exogenous zeitgebers

  Light and Social cues
• Light

  • Helps reset the SCN
  • Light also has an indirect influence on hormone secretion and blood circulation
  • In a study light was detected by skin receptor sites even when not detected by the eyes
  • It can influence the sleep wake cycle
• Social Cues

  • A 6 weeks of age circadian rhythms start and babies' rhythms have been entrained by the schedules imposed by parents
  • This is through mealtimes and bedtimes
  • Research on jet lag suggests adapting to local times for eating and sleeping is an effective way of entraining circadian rhythms and beating jet lag
• AO3 Endogenous Pacemakers: Research support from Shiffre

  • Shiffre's cave study shows how we have internal body clocks that regulate our sleep wake cycle
  • This is due to how he managed to have a sleep wake cycle of around 25 hours despite having no natural light
• AO3 Endogenous Pacemakers: Interactionist System

  • Endogenous Pacemakers cannot be studied in isolation
  • Shiffre's cave study was really rare and he also used artificial light which could have reset his biological clock
  • Pacemakers and zeitgebers interact
  • The more researchers attempt to isolate the influence of internal pacemakers the lower the validity of the research
• AO3 Endogenous Pacemakers: Ethics

  • Animal studies on the sleep wake cycle are justified because they have similar mechanisms
  • The existence of an SCN and pineal gland in the brains of animals means that generalisations can be made to humans
  • However the chipmunk study resulted in many of them dying which was extremely unethical
• AO3 Exogenous Zeitgebers: Case study evidence

  • Evidence challenge the role of exogenous zeitgebers
  • A young blind man from birth had an abnormal circadian rhythm of 24.9 hours
  • Despite exposure to social cues such as regular mealtimes the sleep wake cycle could not be adjusted suggesting social cues are not effective in resetting biological rhythms
• AO3 Exogenous Zeitgebers: Age related insomnia

  • Evidence suggests that people have poorer quality sleep as they get older due to natural changes in the circadian rhythm
  • Exogenous factors may be more responsible for the changes in sleep patterns amongst older people
  • Insomnia is improved if you were more active and exposed to light
• AO3 Exogenous Zeitgebers: Research against

  • 12 people were in a dark cave for 3 weeks going to bed at 11:45 and waking up at 7:45 and the researchers gradually sped up the clock
  • The 24 hours day only lasted 22 hours
  • Only one person could comfortably adjust to the new schedule
  • The existence of a strong circadian rhythm cannot easily be overridden by exogenous zeitgebers
• 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