Infradian and Ultradian rhythms

Question 1

What is the definition of an infradian rhythm?

Answer 1

A biological rhythm of less than one cycle in 24 hours. E.g menstrual cycle

Question 2

What is the menstrual cycle? - relating to infradian rhythms

Answer 2

• Cycle governed by changes in hormone levels
• Typically takes around 28 days for the cycle to complete (time from first day of period to the day before next period)

Question 3

What is the menstrual cycle influenced by?

Answer 3

It is mainly an endogenous system however some exogenous factors such as other womens’ cycles may also influence it

Question 4

Describe Stern and McClintocks study (pheromones on cotton pads)

Answer 4

• 29 women with a history of irregular periods
• Samples of pheromones were gathered from 9 of them at different stages of their cycle and placed on a cotton pad in their armpit (worn for 8 hours)
• They were frozen and rubbed on upper lip of other participants
• On day 1, 20 women were applied with pad from the start of the cycle, on day 2 they were given pads from second day etc
• 68% of women experienced changes to their cycle which brought them closer to their ‘odour donor’

Question 5

What is seasonal affective disorder?

Answer 5

Depressive disorder which has a seasonal pattern of offset and is described as a mental disorder

Question 6

What are the symptoms of SAD?

Answer 6

Low mood and a general lack of interest in life

Question 7

What specific infradian rhythm is SAD?

Answer 7

Circannual - it is subject to a yearly cycle

Question 8

What is believed to be the cause of SAD?

Answer 8

• During the night, the pineal gland secretes melatonin until dawn
• During winter, the lack of light in the morning means the secretion process happens for longer
• This is thought to have an effect on the amount of serotonin produced

Question 9

What is a strength of menstrual synchrony research? (May be explained by natural selection)

Answer 9

• Synchronisation of cycles is thought to have evolutionary value
• For our ancestors, it may have been beneficial for them to menstruate together
• This wouldv’e allowed babies who had lost their mothers to access breast milk
• Therefore it is an adaptive strategy

Question 10

What is a limitation of synchronisation studies? (Methodological shortcomings)

Answer 10

• Other factors such as stress may impact a womans’ cycle which act as confounding variables
• Any supposed pattern of synchronisation is no more than would have been expected to occur by chance
• May explain why other studies have failed to replicate the findings
• Suggests that menstrual synchrony studies are flawed

Question 11

What is the definition of an ultradian rhythm?

Answer 11

A biological rhythm with a frequency of more than one cycle in 24 hours

Question 12

What is the main ultradian rhythm?

Answer 12

Sleep/wake cycle:
- 5 stages of sleep
- Span approximately 90 minutes
- Continues throughout the course of the night

Question 13

What is stage 1 and 2 of the SWC?

Answer 13

Light sleep where we can be easily woken. Stage 1:brain waves are high frequency with short amplitude. Stage 2: The waves continue but there are occasional changes in pattern called sleep spindles

Question 14

What are stages 3 and 4 of the SWC?

Answer 14

Deep sleep/slow wave sleep, brain waves are delta waves with low frequency and high amplitude, it is difficult to wake someone up

Question 15

What is stage 5 of the SWC?

Answer 15

Body is paralysed but the brain activity is similar to an awake brain, rapid eye movement, dreams are often experienced in this stage

Question 16

What is a strength of research into ultradian rhythms? (Helps understand age-related changes in sleep)

Answer 16

• Research shows slow wave sleep decreases with age
• Growth hormones are produced during SWS therefore this is deficient in older people
• The sleep deficit may explain impairments in old age such as reduced alertness

Question 17

What is a limitation of the research into ultradian rhythms? (Significant variation between people)

Answer 17

• Tucker et al found differences between people in terms of the duration of sleep stages, particularly 3 and 4
• This suggests that differences are likely to be biologically determined
• Makes it hard to describe ‘normal sleep’