Infradian and Ultradian

• Infradian rhythms - longer than 24hrs


  eg menstrual cycle - governed by monthly changes in home levels which regulate ovulation - average 28 days

  during each cycle rising levels of the hormone oestrogen cause to ovary to develop an egg and release it, after ovulation hormone progesterone helps the womb lining grow thicker relying the womb for pregnancy, if pregnancy does not occur, the eggs absorbed into body and womb lining comes away and leaves the body (menstrual flow)
• Synchronising the menstrual cycle

  Stern and McClintock studied 29 women with history of irregular periods - samples of pheromones gathered from 9 of women at different stages of their menstrual cycle, cotton pad places in their armpit

  Worn 8 hours to ensure pheromones picked up

  Pads treated with alcohol and frozen- rubbed on upper lip of other participants

  Day one - pads from start of menstrual cycle applied to all 20 women, day two - all given pad from second day of the cycle
• Stern and MClintock findings

  68% women experienced changes to their cycle which brought them closer to the cycle of their odour donor.

  --> menstrual cycle is endogenous system but can be influenced by exogenous factors such as cycles of other women
• Seasonal affective disorder 


  Depressive disorder w seasonal pattern of onset - described and diagnosed as mental disorder in DSM-5

  Persistant low mood, general lack of activity and interest in life.

  Melatonin is implicated in the cause of SAD, during night the pineal gland secretes melatonin until dawn when there is an increase in light - in winter lack of light in morning means this secretion process continues for longer - knock on effect for the production of serotonin in the brain - chemical that's been linked to onset of depressive symptoms.
• Ultradian rhythms -less than 24hrs -stages of sleep

  • Stage 1 and 2 - light sleep person may be easily woken, brain waves high frequency, short amplitude (alpha waves), occasional random changes in pattern called sleep spindles
  • Stage 3 and 4 - deep sleep or slow wave sleep, brain waves are delta waves with a lower frequency and higher amplitude - difficult to wake someone at this point.
  • Stage 5 - REM, body is paralysed yet brain activity closely resembles that of the awake brain, theta waves, eyes occasionally move around, dreams often experienced during REM, can occur during a deep sleep.
• S- infradian: Evolutionary basis

  one strength Menstrual synchrony research may be explained by natural selection

  For our distant ancestors may have been advantages for women to menstruate together and become pregnant at same time - in social group would allow babies who has lost their mothers during or after childbirth to have access to breast milk - improving chances of survival - suggesting synchronisation is an adaptive strategy.
• W: Infradian - methodological limitations

  Methodological shortcomings - many factors may affect change to menstrual cycle including stress, changes in diet exercise etc. These may act as confounding variables, meaning any supposed pattern of synchronisation is no more than would have been expected to occur by chance - may explain why other studies have failed to replicate the findings

  --> menstrual synchrony studies are flawed
• S- Ultradian: improved understanding 


  Improved understanding of age related changes in sleep

  SWS reduces with age - growth hormone is mostly produced during SWS therefore reduced in older people.

  Resulting sleep deficit may explain various issues in old age such as reduced alertness

  In order to increase SWS, relaxation and medication may be used - practical value
• W: Ultradian - individual differences 


  There is significant variation between people - Tucker - found large differences between ppts in terms of duration of each sleep stage, particularly stages 3 and 4. Tucker et al suggest these differences likely to be biologically determined.

  --> difficult to describe normal sleep in any meaningful way, cannot generalise findings to all.