biological rhythms: infradian & ultradian rhythms

• infradian rhythm


  A type of biological rhythm that takes longer than 24 hours to complete
• examples of infradian rhythms

  menstrual cycle & seasonal affective disorder (SAD)
• menstrual cycle


  it is an endogenous pacemaker but it may be influenced by exogenous zeitgebers
• seasonal affective disorder (SAD)

  a depressive disorder which has a season pattern of onset which is diagnosed as a mental health disorder in the DSM-5
• menstrual cycle: Stern & McClintock (1998)


  - 29 women with irregular periods

  - samples of pheromones were gathered (via the armpit on cotton pads worn for at least 8 hours) from 9 of the women at different stages of their cycles

  - the pads were treated via alcohol and frozen , then rubbed on the upper lip of the ppts

  - on day 1 , pads from the 1st day were applied to the 20 women and so on

  - found that 68% of women experienced changes to their cycle which brought them closer to the cycle of their 'odour donor'

  - shows how menstrual cycle;les can synchronise as a result of female pheromones
• main symptoms of seasonal affective disorder (SAD)

  - persistent low mood

  - general lack of activity and interest in life
• Why can SAD be referred to the 'winter blues'?


  It is triggered during the winter months due to the lack of daylight
• What is SAD caused by?

  at night the pineal gland secretes melatonin until the morning , however during winter the lack of light in the morning means the secretion of melatonin continues for longer period of time
• AO3: evolutionary basis of the menstrual cycle (strength)

  - thought to have evolutionary value as it may have been advantageous for females to menstruate together and fall pregnant at the same time

  - so that the babies can be cared for collectively within a social group that was increasing the chances of the offspring's survival
• AO3: practical application to SAD (strength)

  - effective treatment for SAD is phototherapy (light box that simulates strong light in the morning & evening) which is thought to reset melatonin levels and relives symptoms in up to 60% of sufferers
• What did the same study on effective treatment for SAD find?

  It recorded a placebo effect of 30% using a 'sham-negativeion generator' which doubts the chemical influence of phototherapy
• AO3: evolutionary basis of the menstrual cycle (weakness)

  - validity has been questioned of the evolutionary approach

  - Schank (2004) = suggests that if too many women menstruate together that would cause competition for male

  - it would suggest that the avoidance of synchrony would be most adaptive evolutionary strategy and therefore naturally selected
• AO3: methodological limitations of synchronisation studies (weakness)


  - many factors which can affect change in a woman's menstrual cycle ( stress , changes in diet , exercise) and they may act as a confounding variable

  - this means that the supposed patterns of synchronisation seen by McClintock is no more than would have been expected to occur by chance

  - also there were small samples of women used and they use self-report methods which may conflict with the validity of the study
• Trevathan (1993): findings


  Failed to find any evidence of menstrual synchrony in their samples
• ultradian rhythm


  a type of biological rhythm that takes less than 24 hours to complete
• example of the ultradian rhythms

  sleep cycle
• stage 1 & 2 of the sleep cycle

  - light sleep where the person is easily woken

  - brainwave patterns become slower & more rhythmic (alpha waves)

  - patterns become even slower as sleep gets deeper (theta waves)
• stage 3 & 4 of the sleep cycle

  - delta wave which are even slower and have greater amplitude

  - deep sleep or slow wave sleep

  - difficult to rouse a person
• stage 5 of the sleep cycle

  - the body is paralysed

  - brain activity speeds up to the extent it resembles the awake brain

  - Rapid Eye Movement (REM) reflect the fast , jerky activity of the eyes at this point

  - highly correlated with the experience of dreaming
• AO3: improved understanding (strength)


  - research into ultradian rhythms has led to improved understanding of age related changed in sleep

  - sleep scientists observed that sleep stages reduce with age (sleep/wake cycle changes)

  - this as growth hormones are mostly produced during sleep and therefore it is reduced in old people

  - may result in various issues in old age as relaxation and medication may be used to induce a deeper sleep
• AO3: the sleep lab (strength)

  sleep labs use controlled settings and research can exclude extraneous factors ( such as noise , temperature)
• AO3: the sleep lab (weakness)

  Lab studies involve ppts being attached to artificial machinery which can lead to ppts to sleep in a way that doesn't represent normal sleep. This means that findings from the study may lack generalisability .
• AO3: individual differences (weakness)

  - there's a significant variation between people

  - Tucker = found large difference between ppts in terms of duration of each sleep stage ( especially stage 3 & 4)

  - these differences are biologically determined which makes it difficult to describe normal sleep in a meaningful way