infradian and ultradian rhythms

• infradian rhythm

  biological rhythms that occur once a month or once a season (menstraul cycle and seasonal affective disorder) which are entrained by endogenoud pacemakers and exogenous zeitgebers.
• menstrual cycle

  takes around 38 days to cpmplete and is the result of a change in hormone levels including oestrogen rising which causes an egg to develop and be released, then progesterone helps to premier the womb for pregnancy.
• seasonal affective disorder (SAD)

  depressive disorder which has a seasonal pattern. SAD due to the reduced daylight in winter months which means that more melatonin is secreeated which effects the production of serotonin in the brain.
• A01 synchonising the menstrual cycle study

  Exogenous factors the menstrual cycle. 29 women with irregular periods were studied. Samples of phermones (body odour) were gathered from 9 women at different stages of the mestrual cycles from cotton pads placed under thier armpits for >8 hours. Then they wrer rubeed on the top lip of the other particapnts (one for each day of the menstrual cycle).

  They found that 68% of the women experienced changes to thier cycle which brought them closer to the cycle of the 'odour donor
• ultradian rhythms

  a type of biological rhythm that occurs more than once a day such as the sleep cycle (stages of sleep)
• Stage 1 of sleep cycle

  light sleep

  Alpha waves

  muscle activity slows down

  occasional muscle twitching

  part of the sleep esculator
• stage 2 of the sleep cycle

  light sleep
• evolutionary bias - infradian rhythms

  P: strength - menstrual synchrony explained by natural selection

  E: for our ancestors, it was advantageous to menstruate and become pregnant together

  E: in a social group, this meant children whose mothers may have died had access to breast milk increasing their chances of survival

  L: therefore synchronization is an adaptive strategy
• methodological limitations - infradian rhythms

  P: limitation - methodological limitations

  E: factors such as stress may affect the menstrual cycle and so act as a confounding variable

  E: this means that any patterns occurred by chance making it hard to replicate the findings

  L: therefore menstrual synchrony studies are flawed
• improved understanding - ultradian rhythms

  P: strength - improved understanding of age-related changes in sleep

  E: growth hormone is mainly produced during SWS so is reduced in older people

  E: resulting sleep deficit may explain various issues in old age such as reduced alertness

  L: therefore ultradian rhythms have practical value
• individual differences - ultradian rhythms 


  P: limitation - individual differences

  E: researchers found large differences between people during stages of sleep

  E: these differences are most likely biologically determined

  L: therefore it is difficult to describe 'normal sleep'