ultradian and infradian rhythms 10

• • Ultradian rhythms and infradian rhythms are 2 important rhythms that determine human behaviour
  • Ultradian rhythms span a period of less than one day – an example of an ultradian rhythm would be a 90 minute basic rets activity cycle that characterises both our waking and sleeping hours
  • Infradian rhythms span a period longer than one day – an example would be the month menstrual cycle
• Ultradian rhythms

  -          In humans daily cycles of wakefulness and sleep follow the circadian rhythm

  -          Within the sleep portion of this cycle another type of rhythm exists the ultradian rhythm – a biological rhythm shorter then 24 hours – in humans the classic example of this rhythm is the 5 stages that make up a typical night sleep
• ultradian rhythm

  Sleep stages

  -          The ultradian rhythm found in human sleep follows a pattern of alternating REM = rapid eye movement and NREM = non repaid eye movement sleep which consists of stage 1-4

  -          The cycle repeats itself about every 90 -00 minutes throughout the night with different stages having different durations
• ultradian rhythm

  Sleep stages

  -           A complete cycle consists with a progression through the four stages of non rapid eye movement sleep before entering the final stage of rapid eye movement sleep then the whole cycle starts all over again
• ultradian rhythm

  Sleep stages

  -          most of the information we know about the different stages of sleep comes from recording the electrical activities of the brain with each stage showing a different EEG pattern- as a person enters a deep sleep their brain waves slow and their breathing and heart rate decreases during the fifth stage REM sleep the EEG pattern resembles that of an awake person and it is in this stage that most dreaming occurs
• ultradian rhythm

  Sleep stages

  -          stage 1-4 = NREM sleep and final 5th stage = REM sleep
• ultradian rhythm

  Sleep stages

  -          stage 1 = light sleep muscle activity slows down and there is occasional muscle twitching

  -          stage 2= all breathing pattern and heart rate slows and we slightly decrease in body temperature
• ultradian rhythm

  Sleep stages

  -          stage 3= is where deep sleep begins and the brain begins to generate slow delta waves

  -          stage 4= is a very deep sleep where we have rhythmic breathing limited muscle activity and the brain produces delta waves
• ultradian rhythm

  Sleep stages

  -          stage 5 = we experienced rapid eye movement our brain waves speed up and dreaming occurs are muscles relaxed and heart rate increases all breathing also becomes rapid and shallow
• the basic rest activity cycle

  -          kleitman preferred to the 90 minute cycle found during sleep as the basic activity cycle however he also suggested that the 90 minutes ultradian rhythm continues during the day even when we are awake
• the basic rest activity cycle

  -          the difference between the ultradian rhythm in the day and night is that in the day rather than moving through sleep stages we move progressively from a state of alertness into a stage of psychological fatigue approximately every 90 minutes- research suggests that the human mind can focus for a period of about 90 minutes and towards the end of these 90 minutes the body begins to run out of resources resulting in a loss of concentration fatigue and hunger
• the basic rest activity cycle

  -          the operation of the basic rest activity cycle is wakefulness is not as obvious in wakefulness as it is in sleep but Kleitman argued everyday observations provide evidence for it existence for example the familiar 1030 coffee break allows workers to divide the 9:00 AM to noon morning session into 290 minute phases this pattern is repeated in the afternoon with naps more likely to be taken in the mid afternoon
• Infradian rhythms


  infradian rhythms all rhythms that have a duration greater than 24 hours so also longer than a circadian rhythm.
• Infradian rhythms

  -          the cycles my last days weeks months or even be on you.

  -          an infradian  rhythm includes the menstrual cycle in humans which the monthlong cycle there is also the organisation of human activities into weeks / weekly cycles.
• monthly rhythms

  -          menstrual cycle – but there are some considerable variations of the length of this cycle some women experience a relatively short cycle – 23 days where as others experience longer cycles like 36 days – found refinetti although the average appears to be around 28 days
• monthly rhythms

  -          the menstrual cycle is regulated by hormones which either promotes ovulation or stimulate the uterus for fertilisation, ovulation occurs roughly halfway through the menstrual cycle when oestrogen levels peak and this usually lasts for 16 to 32 hours after the ovulatory phase  progesterone levels increase in preparation for the possible implantation of an embryo in the uterus
• monthly rhythms

  -          cycle is controlled by endogenous pacemakers = hormones but also zeitgebers such as other women’s cycles
• monthly rhythms

  -          McClintock took pheromones from 9 women via a cotton pad in there armpit and this was wiped on the upper lip of 20 other women and their menstrual cycles changed – in 68% of women there cycle became closer to the women’s whose pheromones they were exposed to – showing that exogenous zeitgebers affect out pacemakers in regard to the menstrual cycle
• Annual rhythms

  -          In most animals’ annual rhythms are related to seasons for example migration as a response to lower temperatures and decreased food sources in winter but in humans the calendar year appears to influence behaviour regardless of the changes in temperature
• Annual rhythms

  Terman found that seasonal affective disorder was more common in New Hampshire where there is less sunlight in comparison to Florida with a much sunnier climate.

  golden et al carried out a meta-analysis and found the sue of a bright light as treatment for seasonal affective disorder was effective in reducing symptoms.

  both studies show light is an important zeitgeber for seasonal affective disorder,
• Annual rhythms

  -          research suggests A seasonal variation can affect human mood – some people become severely depressed in winter months and this is known as seasonal affective disorder – it is thought that a lack of sunlight during these moths affects the hypothalamus and in turn this lead to increased melatonin which makes you feel sleepy and causes lower levels of serotonin which affects you mood , appetite and sleep and low levels of serotonin are linked to depression
• evaluation 1

  one strength is that there is research evidence to support the ultradian rhythm of sleep.

  -          Dement and Kleitman monitored the sleep patterns of 9 adult participants in a sleep lab.
• evaluation 1

  there brainwaves were recorded on an EEG and researchers controlled for the effects of caffeine and alcohol and found that everyone had periods of REM sleep during the night and if particular participants were woken up during REM sleep they were more likely to recall the dream then in any other sleep cycle – this supports the sleep cycle as being ultradian rhythm that goes through distinct phases one being REM sleep
• evaluation 2

  However, a weakness with this supporting research because there are limitations to Dement and Kleiman’s research when trying to draw a conclusion.

  -          Research was carried out in high controlled condition – the participants pre sleep routines differed form when they were at home and so does there sleep limiting the external validity of the findings making it difficult to draw a conclusion and state that we all go through these stages for the same amount of time at all stages of our lives
• evaluation 2

  -          Eg – Tarokh and carskadon found that the amount of time spent in stage 2 increased by 17% form ages 9-10 age 12-13 – shows there are individual differences in ultradian rhythms of sleep cycles which undermines the generalised finning’s from supporting research.
• evaluation 3

  A strength of research into infradian and ultradian rhythms is that there are practical applications as a result.

  -          - eg in relation to seasonal affective disorder one of the most effective treatments is phototherapy – a lightbox stimulates very strong light y in the morning and evening and is thought to reset melatonin levels

  -          Eastman et al found that this relieve depression symptoms in 60% of suffers supporting that information into infradian rhythms is likely or be accurate if the treatment works.
• evaluation 4

  However, there is some evidence that undermines the practical application of infradian and ultradian rhythm research alongside more conflicting research.

  -          Eastmans study also found a placebo effect of 30% where participants were given a fake generator and were told it was another form of treatment – this questions the extent to which the light is a factor in causing seasonal affective disorder if depressive symptoms can improve without any changes to melatonin and whether seasonal affective disorder is a infradian rhythm
• evaluation 4

  -          Yang and Schank found conflicting research after collecting data in 186 Chinese women and their menstrual cycles over a year who lived in dorms together and found that women living in groups did not synchronise their cycles – which questions particularly infradian rhythms in terms of the influence of exogenous zeitgebers suggesting the menstrual cycle may not only be due to internal biological factors