Biological rhythms: infradian and ultradian rhythms

• Biological rhythms: infradian and ultradian rhythms

  Infradian rhythms

  The menstrual cycle

  Is governed by monthly changes in hormone levels which regulate ovulation. Takes approx 28 days to complete. During each cycle, rising levels of oestrogen cause the ovary to develop an egg and release it (ovulation), and progesterone helps the womb lining grow the thicker.
• Biological rhythms: infradian and ultradian rhythms 2

  Infradian rhythms

  Research study

  Although the menstrual cycle is an endogenous system, evidence suggests that it may be influenced by exogenous factors, such as the cycles of other women. Stern and McClintock (1998) showed how menstrual cycles may synchronise cos of the influence of female pheromones. Involved 29 women w/ history of irregular periods. Samples of pheromones were gathered from 9 of the women at diff stages of their cycles via a cotton pad placed in their armpit, which were rubbed on the upper lip of the other ppts.
• Biological rhythms: infradian and ultradian rhythms 3

  Infradian rhythms

  Research study (findings)

  68% women experienced changes to their cycle which brought them closer to the cycle of their 'odour donor'.
• Biological rhythms: infradian and ultradian rhythms 4

  Infradian rhythms

  Seasonal affective disorder (SAD)

  A depressive disorder which has a seasonal pattern of onset. Main symptoms are persistent low mood and a general lack of activity and interest on life. Referred to as 'winter blues' as symptoms are triggered during the winter months when the number of daylight hours becomes shorter. A circannual rhythm as it is subject to a yearly cycle. However could be classed as a circadian rhythm as may to due to disruption of the sleep/wake cycle due to prolonged periods of daily darkness.
• Biological rhythms: infradian and ultradian rhythms 5

  Infradian rhythms

  Seasonal affective disorder (SAD) 2

  Psychologists have hypothesised that the hormone melatonin is implicated in the cause of SAD. During the night, the pineal gland secretes melatonin until dawn when light levels increase. During winter, lack of light in morning means this secretion process continues for longer. Thought to have a knock-on effect on production of serotonin in the brain (linked to onset of depressive symptoms).
• Biological rhythms: infradian and ultradian rhythms 6

  Ultradian rhythms

  The sleep cycle is an ultradian rhythm- 5 distinct stages of sleep that altogether span approx 90-minutes.

  Stages 1 and 2 are light sleep where the person may be easily woken. Brain patterns become slower and more rhythmic (alpha waves), becoming slower as sleep becomes deeper (theta waves).
• Biological rhythms: infradian and ultradian rhythms 7

  Ultradian rhythms 2

  Stages 3 and 4 involve delta waves which are slower still and have a greater amplitude than earlier wave patterns. This is deep sleep or slow wave sleep and it is difficult to rouse someone.

  In stage 5, REM sleep, the body is paralysed yet brain activity speeds up significantly and resembles a wake brain. Stands for rapid eye movement to denote the fast, jerky activity of the eyes under the eyelid. Research suggests REM activity is highly correlated w/ the experience of dreaming.
• Biological rhythms: infradian and ultradian rhythms- evaluation

  Methodological limitations in synchronisation studies. Commentators argue there are many factors that may effect change in woman's menstrual cycle (e.g., stress, changes in diet) that may act as confounding variables. Means that patterns of synchronisation (McClintock) is no more than would have been expected to occur by chance. Furthermore, research typically involves small samples of women and relies on women self-reporting the onset of their own cycles.
• Biological rhythms: infradian and ultradian rhythms- evaluation 2

  Evidence supports the idea of distinct stages in sleep. Dement and Kleitman (1957) monitored sleep patterns of 9 adult ppts in a sleep lab. Brainwave activity was recorded on an EEG and the researchers controlled for effects of caffeine and alcohol. REM activity was hihgly correlated w/ experience of dreaming, brain activity varied according to how vivid dreams were, and ppts woken during dreaming reported very accurate recall of their dreams. Replications = similar findings but small sample size is criticised.
• Biological rhythms: infradian and ultradian rhythms- evaluation 3

  Menstrual synchrony, of the kind observed in the McClintock study, is thought to have an evolutionary value. It may have been advantageous for females to menstruate together and therefore fall pregnant around the same time, as new-borns could be cared for collectively within a social group, increasing the chances of its survival. However, the validity of the evolutionary perspective has been questioned. Schank (2004) argued that if their were too many females cycling together, this would produce competition for the highest quality males (and thereby lowering the fitness of any potential offspring).