Infradian and ultradian

• What are the weaknesses of research into infradian and ultradian rhythms?

  in 1999 Gloth also found that phototherapy (exposure to bright light) was an ineffective treatment for SAD, questioning the role of light levels as exogenous zeitgeber in ultradian rhythms.

  
  

  Mclintocks study was a field experiment meaning that extraneous variables were not controlled e.g. diet, exercise levels, or pollution could have affected the change in menstrual cycles. Additionally trevalthan (1993) found no synchronisation amongst women during a similar experiment. This questions the validity of the research raising doubts about weather pheromones as exogenous zeitgebers are influential in Infradian rhythms.
• What are the strengths of research into infradian and ultradian rhythms?

  practical applications in treatment for SAD. Now we know it is affected by light levels, vitamin D supplements can be used to reduce its effect which can be seen by gloths 1999 study showing SAD patienst treated with vitamin D reported an average of 74% improvement.
• What is the support for the sleep cycle being an ultradian rhythm?

  Dement and Kleitman (1957) who studied 33 adults with EEG scans and found that the researchers found that for 126 nights discrete periods of rapid eye movement potentials were recorded without exception. And participants could only accurately recall dreams when awoken during REM, it was concluded that sleep cycles repeated throughout the night and occur in distinct stages.
• What are ultradian rhythms?

  biological rhythms in which the cycle lasts less than 24 hours e.g. the cycles of sleep where stages 1 and 2 represent the 'sleep escalator' where the participant can easily be awoken, stages 3 and 4 show deeper and slower delta waves, and stage 5 represents REM that is closely associated with dreaming.
• What is the support for the menstrual cycle being an infradian rhythm?

  McLintock et al. (1998) who found that the menstrual cycles of women became synchronised after being exposed to a 'donor' pheromone which acted as an exogenous zeitgeber.
• What are infradian rhythms?

  biological rhythm in which the cycle lasts more than 24 hours. E.g. menstrual cycle lasting around 28 days and affected by hormonal levels, and seasonal affective disorder that is experienced during darker months where more melatonin is secreted causing higher depression levels.
• elaborate on the menstrual cycle as an infradian rhythm?

  The menstrual cycle is governed by hormones roughly on a 28 day basis. Oestrogen levels rise to release an egg from the ovary and progesterone helps the womb lining to grow. If there is no pregnancy then the womb lining sheds. Stern and McClintock (1998) found that women could synchronise their periods by being exposed to other womens’ pheromones. 
• elaborate on SAD as an infradian rhythm?

  SAD is a type of depressive disorder. When there are reduced daylight hours in the winter it can trigger a low mood. This is because at night our pineal glad detects the dark and produces a hormone called melatonin. In the winter it is darker first thing in the morning and so this tricks the brain in producing melatonin for longer. This can affect the production of serotonin, which is linked to the depressive symptoms. SAD is called a circannual rhythm as it can also be considered a circadian rhythm due to the disruption of the sleep-wake cycle.
• what are the strengths of infradian rhythms?

  RWA

  can have an evolutionary basis
• elaborate on RWA as a strength of infradian rhythms?

  One strength of research into infradian rhythms is that it has good real world application. For example, a lightbox can be used to reset melatonin levels and relieve symptoms in up to 80% of SAD patients (Sanassi, 2014). However, light therapy can causes headaches and eye strain, as well as many people reporting a relapse in symptoms the following winter. It is suggested that CBT may be more effective than light therapy in treating SAD. Therefore, light therapy may not be considered a good real world application after all.
• elaborate on evolution as a strength of infradian?

  the menstrual cycle could be explained through evolutionary explanations, such as natural selection. Stern and McClintock suggested that it was adaptive for women to synchronise their cycles as they could become pregnant at the same time. This would mean that if their were any mothers who died in childbirth there would be other mothers who could take on the breastfeeding of that child. Therefore, this suggests that menstrual synchrony is an adaptive behaviour based on use living in social groups in the past.
• what are the weaknesses of infradian rhythms?

  However, there is criticism of the research into menstrual synchrony. There are many external factors that can influence a woman’s menstrual cycle, for instance stress and diet. These could be the cause of changes in menstrual cycles and so are acting as confounding variables. Other studies have also failed to replicate Stern and McClintock and so this could be the reason why. This suggests that Stern and McClintock’s study lacks validity.
• what are ultradian rhythms?

  Ultradian rhythms are ones that take less than 24 hours and occur more than once a day, for example the sleep cycle.
• what is the first and second stage of the sleep cycle?

  Stages 1 and 2 involve light sleep where you can be easily woken. In stage 1 alpha waves are produced and in stage 2 alpha waves continue but with sleep spindles (occasional random changes). 
• what are stage three and four of the sleep cycle?

  Stages 3 and 4 involve deep sleep or slow wave sleep. The brain produces slower delta waves which have a lower frequency and higher amplitude. It is more difficult to wake someone up in these stages. 
• what is stage five of the sleep cycle?

  Lastly, stage 5 is when we experience rapid eye movement (REM) sleep. The body is paralysed and the activity of the brain resembles someone who is awake. It produces theta waves and the eyes sometimes move around. This is when dreams are most likely to occur.
• what are the strengths of ultradian rhythms?

  scientific methods

  RWA
• elaborate on scientific methods as a strength of ultradian?

  A strength of research into ultradian rhythms is that it uses scientific methods to investigate sleep. Using EEGs to record sleep brain wave activity is very controlled and produces objective data and thus increases the validity of the findings. 
• elaborate on RWA as a strength of ultradian?

  However, another strength of research into ultradian rhythms is that it has good real world application. Researchers now understand that older people have less slow wave sleep, when normally growth hormone would be released. This can explain some of the issues that older people have such as decreased alertness and we can recommend medications and relaxation techniques to help them with the quality of sleep. Therefore, this suggests that our understanding of ultradian rhythms has practical value of some individuals.
• what are the weaknesses of ultradian rhythms?

  individual differences

  invasive
• elaborate on individual differences as a weakness of ultradian?

  A limitation of ultradian rhythms is that it does not take into account individual differences. Tucker et al. (2014) has found large differences between the durations of each stage for different people suggesting it is difficult to generalise stages of sleep to everyone. In fact, it is suggested that biological differences could be the cause of these differences and so our knowledge of ultradian rhythms is limited.
• elaborate on invasive as a weakness for ultradian?

  However, being attached to an EEG can be invasive and disturb the sleep of those taking part. Therefore, this could affect the results and so it can be argued that this type of research could lack ecological validity as it tells us nothing about our sleep on a day to day basis.