Biological rhythms: Ultradian and infradian

Question 1

What is an infradian rhythm? (+example)

Answer 1

A biological rhythm that occurs over multiple days (the menstrual cycle, SAD)

Question 2

What is an ultradian rhythm? (+example)

Answer 2

A biological rhythm that occurs multiple times in a day (the sleep cycle (not the sleep/wake cycle))

Question 3

How has research into the menstrual cycle provide evidence in support of exogenous zeitgebers?

Answer 3

• Stern and McClintock (1998) did a study showing how menstrual cycles can synchronise as a result of female pheromones
• Pheromones of 9 women with histories of irregular periods were collected at different stages of their menstrual cycles via a cotton pad placed in their underarm
• These pads were frozen and rubbed on the upper lip of 20 other participants and it was found that 68% of them had changes in their cycles which brought them closer to the cycle of their ‘odour donor’
• This shows that extraneous stimuli can affect internal clocks

Question 4

What is SAD?

Answer 4

• Seasonal affective disorder
• Circannual rhythm
• Less melatonin is released during winter months due to low levels of light, causing a seasonal depression

Question 5

Describe the 5 stages of the sleep cycle

Answer 5

• Cycle lasts a total of around 90 minutes
• Stages 1&2: light sleep- person may be easily woken, brain waves get slower, deeper and more rhythmic (alpha->theta)
• Stages 3&4: deep sleep- difficult to wake, slower brain waves (delta)
• Stage 5: REM- the body is paralysed, brain speed speeds up resembling an awake brain- REM activity very likely to be related to dreams and sleepwalking

Question 6

What are some evolutionary advantages and disadvantages of synchronising menstrual cycles?

Answer 6

(+) Children are raised together/mothers are pregnant together
(-) Having synchronised menstrual cycles would create more ‘competition’ for higher quality males

Question 7

What are the methodological drawbacks of McClintock’s study?

Answer 7

• Things such as stress, diet and exercise could have an impact on a woman’s menstrual cycle
• Other studies have been unable to produce results which support hers (Trevathan et al 1993)

Question 8

What evidence is there to support the ideas of the sleep cycle?

Answer 8

• Dement and Kleitman (1957) used caffeine and alcohol and recorded their brain activity with an EEG and asked participants to report on the vividness of their dreams
• It was seen that higher levels of brain activity was correlated with more vivid dreams

Question 9

How can findings on infradian rhythms have practical applications?

Answer 9

• Findings on SAD can result in developments for appropriate treatments such as light boxes
• Light box proven to be effective in Eastman et al study (1998) relieved symptoms in 60% of sufferers compared to 30% of a placebo group