infradian & ultradian rhythms

• ultradian rhythms 


  a cycle shorter than one day

  (sleep stages)

  there are several different types of sleep that we move between throughout the night in a regular pattern

  in sleep the cycles occur approximately every 90-100 minutes

  different stages of sleep within these cycles
• 5 stages of sleep 


  1-drowsiness 2-light sleep 3/4- deep sleep 5-REM
• stage 1


  approximately 15 minutes

  becomes relaxed, brain activity from different parts of the brain are synchronised

  stage can be regarded as drowsiness

  transition from awake to stage 1 is often accompanied by a hypnogogic state - hallucinatory images might be experienced
• stage 2


  approximately 20 minutes

  EEG waves become slower & larger but with short bursts of high frequency sleep spindles

  k-complexes are also characterise of stage 2 - brains response to external stimuli (noises in room)

  quite easy to be awakened at this stage
• stage 3 


  approximately 15 minutes

  sleep deepens as brain waves slow down
• stage 4 


  slow wave sleep (sws)

  approximately 30 minutes

  deeper stage of sleep than any of first 3 stages

  hard to wake someone up in this stave

  growth hormones secreted

  sleepwalking and talking can occur & night terrors
• stage 5 


  REM

  last approximate 10 minutes in 1st cycle - builds up to an hour by 4&5th cycle

  most dreaming occurs here - increased brain activity and voluntary muscles becomes paralysed otherwise we would all act out our dreams - brain wave activity same as when awake
• progression through sleep cycle

  after sleep has worked through first 4 stages of progressively deeper sleep, the reverse the process - stage 4 sleep then stage 3 then stage 2 - stage 2 then followed by REM

  after REM , sleeper starts another cycle from stage 2

  most sleepers complete about 5 cycles during a normal nights sleep with progressively less SWS and REM as morning approaches
• infradian rhythm

  longer than 24 hours (menstrual cycle)

  controlled by hormones - endogenous pacemaker

  oestrogen & progesterone are released into blood stream and effect the ovaries and uterus - average cycle is 28 days - huge variations between women

  during each cycle rising levels of oestrogen cause the ovary to develop and realease an egg (ovulation) after ovulation progesterone helps the womb lining thicken - readying body for pregnancy

  if no pregnancy - egg absorbed into body - womb lining comes away and leaves body - menstrual flow
• strength of ultradian rhythms 


  evidence to support different stages of sleep - study which the sleep patterns of 9 adults was monitored in sleep lab

  brainwave activity was measured on an EEG - evidence found to support the idea of different stages of sleep

  REM activity during sleep was highly correlated with the experience of dreaming (more activity when dreaming)

  brain activity varied according to how vivid dream was
• criticism of ultradian rhythms


  individual differences in time and duration of peoples ultradian rhythms. in one study p's spent 11 days and nights in a sleep lab - there were large individual differences between p's sleep duration, time taken to fall asleep and time spent each each sleep stage = sleep stages proposed may not generalise to everyone
• strength of the study

  study supports the idea that sleep is at least partially determined by endogenous pacemakers - all p's were in same controlled sleep lab environment so it cant be external factors causing individual differences that were observed = evidence suggests differences are biological (controlled by endogenous pacemakers) and maybe even genetic
• strength of infradian rhythm


  menstrual cycle is an endogenous system - evidence suggests it can also be influenced by exogenous factors

  when several women (not taking oral contraceptives) live together their menstrual cycle synchronise - pheromones effect the bodies that are close to them

  one study - daily samples of sweat collected from one group of women and rubbed onto lips of another group - groups kept separate but women's menstrual cycles synchronised with their donor - shows that another persons pheromones (exogenous factor) can impact the menstrual cycle
• strength of infradian rhythm 


  evolutionary advantage for s social group to have synchronised menstrual cycles so the women would become pregnant at the same time. - all women breast feed at same time so childcare could be shared - evident in many female mammals in wild (and Efe tribe in Zaire)

  • but , new explanation of synchronisation is evolution advantageous for another reason = may stop all the women getting pregnant from one single male
• weakness of infradian rhythm 


  methodological issues with many of the synchronisation studies conducted - many factors may effect change in women's menstrual cycle (stress, changes in diet and exercise) - might act as confounding variables

  the research also involves small sample and relies on p's self reporting their own cycle