biological rhythms: infradian rhythms

Question 1

What is an infradian rhythm?

Answer 1

A type of biological rhythm that takes longer than 24 hours to complete

Question 2

What are examples of infradian rhythms?

Answer 2

menstrual cycle & seasonal affective disorder (SAD)

Question 3

menstrual cycle

Answer 3

it is an endogenous pacemaker but it may be influenced by exogenous zeitgebers

Question 4

What is seasonal affective disorder (SAD)?

Answer 4

a depressive disorder which has a season pattern of onset which is diagnosed as a mental health disorder in the DSM-5

Question 4

Stern & McClintock (1998) menstrual cycle study

Answer 4

• 29 women with irregular periods
• samples of pheromones were gathered (via the armpit on cotton pads worn for at least 8 hours) from 9 of the women at different stages of their cycles
• the pads were treated via alcohol and frozen , then rubbed on the upper lip of the ppts
• on day 1 , pads from the 1st day were applied to the 20 women and so on
• found that 68% of women experienced changes to their cycle which brought them closer to the cycle of their ‘odour donor’
• shows how menstrual cycle;les can synchronise as a result of female pheromones

Question 5

What are the main symptoms of seasonal affective disorder (SAD)?

Answer 5

• persistent low mood
• general lack of activity and interest in life

Question 6

Why can SAD be referred to the ‘winter blues’?

Answer 6

It is triggered during the winter months due to the lack of daylight

Question 7

What is SAD caused by?

Answer 7

at night the pineal gland secretes melatonin until the morning , however during winter the lack of light in the morning means the secretion of melatonin continues for longer period of time

Question 8

How is the evolutionary basis of the menstrual cycle a strength of infradian rhythms?

Answer 8

• thought to have evolutionary value as it may have been advantageous for females to menstruate together and fall pregnant at the same time
• so that the babies can be cared for collectively within a social group that was increasing the chances of the offspring’s survival

Question 9

How is practical application to SAD a strength of infradian rhythms?

Answer 9

• effective treatment for SAD is phototherapy (light box that simulates strong light in the morning & evening) which is thought to reset melatonin levels and relives symptoms in up to 60% of sufferers

Question 10

What did the same study on effective treatment for SAD find?

Answer 10

It recorded a placebo effect of 30% using a ‘sham-negativeion generator’ which doubts the chemical influence of phototherapy

Question 11

How is the evolutionary basis of the menstrual cycle a weakness of infradian rhythms?

Answer 11

• validity has been questioned
• Schank (2004) = suggests that if too many women menstruate together that would cause competition for male
  
  • it would suggest that the avoidance of synchrony would be most adaptive evolutionary strategy and therefore naturally selected

Question 12

How is the methodological limitations of synchronisation studies a weakness to infradian rhythms?

Answer 12

• many factors which can affect change in a woman’s menstrual cycle ( stress , changes in diet , exercise) and they may act as a confounding variable
• this means that the supposed patterns of synchronisation seen by McClintock is no more than would have been expected to occur by chance
• also there were small samples of women used and they use self-report methods which may conflict with the validity of the study

Question 13

What did Trevathan (1993) find?

Answer 13

Failed to find any evidence of menstrual synchrony in their samples