Infradian & ultradian rhythms

What is an infradian rhythm?

A biological rhythm that takes longer than 24 hours to complete

What are 2 examples of infradian rhythms?

The female menstrual cycle & SAD

What is SAD?

Seasonal Affective Disorder: a type of depression, which occurs in the winter months where there is an absence of natural daylight

The menstrual cycle is an example of an endogenous system but it is also affected by exogenous factors. What is an example?

Cycles can synchronise with other females

What is an ultradian cycle?

A biological rhythm that takes less than 24-hours to complete

What is an example of an ultradian rhythm?

The stages of sleep

How many distinct stages of sleep are there?

5

How long do the stages of sleep last?

90 minutes & repeats 4-5 times over the course of a night’s sleep

What happens in stage 1 & 2?

Light sleep, where the person is easily woken & brainwaves slow from alpha to theta

Which type of brainwave patterns are associated with these early stages of sleep?

Alpha

As sleep becomes deeper, what type of brainwaves can be detected?

Theta

What type of brain wave is associated with stages 3 & 4?

Delta

These waves are slower still & have higher amplitude than stages 1 & 2. What type of sleep does this indicate?

Deep sleep

What type of sleep is characteristic of stage 5?

REM (Rapid Eye Movement) sleep

What happens to brain activity during REM sleep?

Speed increases significantly in a manner that resembles the awake brain

With which stage would you correlate dreaming?

Stage 5

Outline and evaluate infradian and/or ultradian rhythms (16 marks)

Write your AO1 paragraph

• Infradian rhythms are a type of biological rhythm that lasts longer than 24-hours, such as the female menstrual cycle & Seasonal Affective Disorder (SAD). The menstrual cycle lasts around 28 days & is regulated by hormonal changes. Rising oestrogen levels trigger ovulation, while progesterone thickens the womb lining, preparing for pregnancy. If pregnancy doesn’t occur, the egg is absorbed & the uterus lining leaves as menstrual flow. The menstrual cycle is an example of an endogenous system, but it can also be affected by exogenous factors (e.g. synchronisation with other women).

• Ultradian rhythms are another type of biological rhythm that lasts less than 24-hours (e.g. the stages of sleep). There are 5 distinct stages lasting 90 minutes each & repeating 4-5 times throughout the night. Stages 1-2: light sleep, where the person is easily woken & brainwaves slow from alpha to theta. Stages 3-4: deep sleep, where the person is more difficult to wake, characterised by slow delta waves. Stage 5 (REM – Rapid Eye Movement - sleep): brain activity speed increases, resembling the awake brain; this stage is correlated with dreaming.

Outline and evaluate infradian and/or ultradian rhythms (16 marks)

Write your strength AO3 PEEL (real-world applications)

• Point: One strength of infradian rhythms is that they have real-world applications.

• Evidence: For example, light boxes that provide artificial exposure to bright light in the morning & evening in the dark, winter months are used to alleviate symptoms of SAD.

• Explain: Research has also found that light box therapy can relieve depressive symptoms in up to 60% of individuals with SAD, highlighting its effectiveness.

• Link: Therefore, not only does this improve individuals’ wellbeing, but also has economic benefits, as it reduces the demand & strain on NHS mental health services.

Outline and evaluate infradian and/or ultradian rhythms (16 marks)

Write your strength AO3 PEEL (Russell et al.)

• Point: One strength of infradian rhythms is there is research evidence to support that they are influenced by exogenous zeitgebers.

• Evidence: For example, Russell et al. found that female menstrual cycles became synchronised with other females through odour exposure, despite the two groups being separate.

• Explain: This suggests that pheromones, acting as exogenous zeitgebers, can affect the timing of menstrual cycles in nearby individuals, even without direct contact.

• Link: Therefore, this highlights how infradian rhythms can be shaped by exogenous zeitgebers, showing their relevance in understanding human biological & social interactions.

Outline and evaluate infradian and/or ultradian rhythms (16 marks)

Write your limitation AO3 PEEL (methodological issues)

• Point: One limitation of infradian rhythms is that some synchronisation studies suffer from methodological issues.

• Evidence: For example, many factors (e.g. stress, diet & exercise) can act as confounding variables, meaning researchers cannot confidently conclude that synchronisation is solely due to pheromones.

• Explain: Additionally, these studies often rely on small sample sizes & participants self-reporting their cycles, which increases the risk of social desirability bias.

• Link: Overall, this reduces the internal validity of such studies & limits the generalisability of the findings, making it difficult to draw firm conclusions about menstrual synchronisation.