Infradian rhythms

• What is an Infradian rhythm?

  Lasts more than 24 hours
• What is an example of an Infradian rhythm?

  The menstrual cycle
• What does follicle stimulating hormone?

  Stimulates a follicle to ripen an ovum and release oestrogen
• What does progesterone do?

  Prepares the lining of the womb for pregnancy. If no pregnancy occurs the lining of the womb sheds
• What did Penton Voak et al (1999) find?

  If females are fertile they are more likely to choose a partner with a more masculine face as his alleles are more desirable (increasing reproductive fitness)

  If not fertile they will choose a more feminised face as his alleles are less desirable, so he won’t cheat
• What system is the menstrual cycle?

  Endogenous
• What can affect the menstrual cycle?

  Exogenous factors
• What is an example of an exogenous factor that affects the menstrual cycle?


  The cycle of other women (menstrual synchrony)
• What are pheromones?

  Odourless chemicals
• What did McClintock do to investigate menstrual synchrony?

  Rubbed sweat on the upper lip of 20 women, 68% experienced changes to their menstrual cycle that brought them closer to that of their odor donor
• What is an evolutionary benefit of menstrual synchrony?

  May have been advantageous for females to menstruate together as they will become pregnant at the same time, so babies could’ve been cared for collectively, increasing survival
• What did Schank (2004) find about menstrual synchrony?


  If there were too many synchronised females there would be more competition for high quality males, so women would have to settle for lower reproductive fitness
• What is an issue with investigating menstrual synchrony?

  Confounding variables may have influenced the cycles of the women such as stress or diet

  Also the results rely on self report which may not be accurate

  Travathen (1993) - menstrual synchrony doesn’t exist
• What is seasonal affective disorder?

  A circannual rhythm that means people are depressed during winter
• What hormone is secreted in response to light?

  Melatonin
• Which neurotransmitter does melatonin have an affect on?

  Serotonin
• When is melatonin secreted?

  As light decreases
• What does more melatonin cause?

  Depressive symptoms
• What is phototherapy?

  A treatment for SAD that involves exposure to light to decrease melatonin levels
• What did Eastman do to investigate phototherapy?

  Randomly assigned 96 Ps to one of 3 different conditions:

  • Bright light treatment in morning
  • Bright light treatment in evening
  • A morning placebo of normal light

  Found that people in the morning light after 3 weeks were in near-total remission of their symptoms. Evening light was better than placebo but worse than morning light
• What was an issue with Eastman’s phototherapy study?

  30% of sufferers in the placebo improved, so SAD must have a psychological component to it