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Infradian and Ultradian

Infradian Rhythms– a type of biological rhythm with a frequency of less than one cycle in 24 hours- rhythms last longer than 24 hours (longest)

SAD is an infradian rhythm

  • Depressive disorder with a seasonal pattern
  • SAD is an infradian rhythm called a circannual (yearly) cycle
  • SAD may be caused by melatonin
  • During the night, the pineal gland secretes melatonin until dawn when there is an increase of light
  • During winter, the lack of light means secretion goes on for longer
  • This has a knock-on effect in the production of serotonin in the brain (less)

Menstrual Cycle

  • Infradian rhythm
  • Endogenous
  • Regulated by hormones that either promote ovulation (oestrogen) or stimulate the uterus for fertilisation (progesterone)
  • Ovulation occurs roughly halfway through the cycle when oestrogen levels are highest- usual lasts for 16-32 hours
  • Progesterone levels increase after ovulation for possible implantation of an embryo- thickens lining
  • Usual cycle is 28 days- but varies between women
  • (Stern and McClintock studied 29 women with irregular periods)
  • (Pheromones were taken from some at different stages of their cycles via a cotton pad under the armpits- these pads were cleansed and then put on the upper lips of the other participants- 68% of women experienced changes to their cycle which brought them closer to the cycle of the other women)

Hibernation in animals

 

Ultradian Rhythms– a type of biological rhythm with a frequency of more than one cycle in 24 hours, such as the stages of sleep – rhythms last fewer than 24 hours (shortest)

Stages of Sleep

  • This cycle alternates between REM and NREM (non-rapid eye movement) sleep and consists of 5 stages
  • The cycle starts at light sleep progressing to deep and them REM sleep where brain waves speed up and dreaming occurs
  • This repeats itself about every 90 minuets throughout the night
  • A complete sleep cycle goes through the four stages of NREM sleep before entering REM (stage 5) and then repeating. Research using EEG has highlighted distinct brain waves patterns during the different stages of sleep
  • Stages 1 and 2 are ‘light sleep’ stages. During these stages’ brainwave patternsbecome slower and more rhythmic, starting with alpha waves progress to theta waves
  • Stages 3 and 4 are ‘deep sleep’ or slow wave sleep stages, where it is difficult to wake someone up. This stage is associated with slowerdelta waves
  • Finally, Stage 5 is REM (or dream) sleep. Here is the body is paralysed (to stop the person acting out their dream) and brain activity resembles that of an awake person
  • AO3
    • Strength- Menstrual cycle- as evolutionary basis
    • In the past, advantage for females to menstruate together and therefore fall pregnant around the same time
    • This would mean that new-borns could be cared for collectively within a social group, increasing the chances of the offspring’s survival
    • However, the validity of the evolutionary perspective has been quested by some
    • Jeffrey Schank- argued that if there were too many females with synchronised cycles in one social group- this would produce competition for the height quality males
    • From this view- the avoidance of synchronicity would appear to be the most adaptive evolutionary strategy
    • Limitation- don’t take into account individual differences
    • The problem with studying sleep cycles is the differences observed in people, which make investigating patterns difficult. 
    • Tucker et al. (2007)found significant differences between participants in terms of the duration of each stage, particularly stages 3 and 4 (just before REM sleep).
    • This demonstrates that there may be innate individual differences in ultradian rhythms, which means that it is worth focusing on these differences during investigations into sleep cycles.
    • In addition, this study was carried out in a controlled lab setting, which meant that the differences in the sleep patterns could not be attributed to situational factors, but only to biological differences between participants.
    • While this study provides convincing support for the role of innate biological factors and ultradian rhythms, psychologists should examine other situational factors that may also play a role.
    • External factors have an effect on Infradian Rhythms
    • Research suggests that the menstrual cycle is, to some extent, governed by exogenous zeitgebers (external factors). Reinberg (1967) examined a woman who spent three months in a cave with only a small lamp to provide light.
    • Reinberg noted that her menstrual cycle shortened from the usual 28 days to 25.7 days.
    • This result suggests that the lack of light (an exogenous zeitgeber) in the cave affected her menstrual cycle, and therefore this demonstrates the effect of external factors on infradian rhythms.