Ultradian and Infradian rhythms

• ultradian rhythms are rhythms that last shorter than 24 hours
• examples of ultradian rhythms includes sleep stages and basic rest activity cycle (BRAC)
• BRAC stands for basic rest activity cycle
• sleep stages is an example of an ultradian rhythm
• basic rest activity cycle is an example of an ultrdian rhythm
• sleep stages

  • ultradian rhythms found human sleep follows pattern of altering REM and NREM sleep which consisted of stages 1 to 4 (different stages have differing durations)
  • the complete cycle consists of progression through 4 stages of NREM sleep before entering final stage of REM sleep
  • we know there are different stages due to the recording of electrical activities in the brain (EEG)
  • as person enters deep sleep the brain waves slow - breathing and heart rate decrease
• basic rest activity cycle (BRAC)

  • kleitman referred 90 min cycle found during sleep the the basic rest activity cycle
  • suggested 90 min rhythm continues in day - instead of moving through sleep stages you move through state of alertness into state of fatigue every 90 min
  • research suggests human mind can focus for period of 90 min and towards end of 90 min the body begins to run out of resources - loss of concentration
• infradian rhythms are rhythms that have a duration greater than 24 hours
• infradian rhythms may have cycles lasting up to days, weeks, months and annually
• examples of infradian rhythms include menstrual cycle and the organisation of human activities into weeks
• weekly rhythms are an example of infradian rhythms
• weekly rhythms

  • infradian rhythm
  • obvious differences in human behaviour conform to weekly cycle
  • example - young couples report more sexual activity at weekends due to male hormone levels increasing
• monthly rhythms are an example of an infradian rhythm
• monthly rhythms such as menstrual cycle

  • womens reproductive cycle is infradian rhythm as it lasts about a month
  • considerable variations in length of cycle with some women having 26 days and others 36
  • menstrual cycle is regulated by hormones either promoting ovulation or stimulating uterus for fertilisation
• annual rhythms

  • calendar year appears to influence behaviour
  • research suggests seasonal variation in mood in humans with some people seriously depressed in winter months
  • winter is associated with increase in heart attacks
• evaluation - individual differences

  • study by tucker et al suggests differences in sleep patterns are biologically determined and may be genetic in origin
  • participants were studied for 11 days and nights in controlled lab environment
  • researcher assessed sleep duration, time to fall asleep and amount of time in each sleep stage - found large differences in each characteristic
  • doe sleep (stage 3 and 4) is were individual differences were significant showing differences were not driven by circumstance but can be partially determined
• evaluation - research support for BRAC

  • support for importance of BRAC from studies of elite performers
  • ericson et al studied group of elite violinist and found practice sessions were limited to no more than 90 min - practice was distributed during day in 90 min segments
  • analysis also indicated violinists frequently napped to recover from practice
  • outlines individuals in order to perform well should have sessions of 90 min intervals then rest
• evaluation - menstrual cycle - exogenous cues

  • menstrual cycle can be controlled by exogenous cues such as when several women live together and do not take contraceptives their menstrual cycle tends to synchronise
  • study - dialy samples sweat collected from group of women and then rubbed onto upper lips of women in second group
  • groups were separated yet menstrual cycles became synchronised with 'odour donor' - russell et al
  • suggests synchronisation of menstrual cycle can be affected by pheromones (act in similar way to hormones but affects bodies of people close by)
• evaluation - menstrual cycle and mate choices

  • penton voak et al suggests human mate choices vary across the menstrual cycle
  • women generally expressed preferences for 'slight feminised' faces when picking for long term relationship
  • BUT - when in ovulation phase women showed preferences for more masculine faces
  • preferences believed to represent preference of kindness and cooperation in parental care in long term mates but preference for males with 'good genes' for short term liaisons so genes may be passed to offspring
• evaluation - belief in lunar rhythms

  • belief in infradian rhythm based on phases of moon remains strong
  • example - midwives believe more babies are born during full moon than during new moon - stats show this is purely subjective association
  • likewise - surveys of workers in mental health professionals have shown persistent belief in full moon altering behaviour
  • ultimately some individuals belief lunar rhythm is infradian rhythm but there is no solid evidence to support