Infradian Rhythms

Question 1

What are Infradian rhythms?

Answer 1

Cyclical patterns within biological systems that last longer than 24 hours (eg. Menstrual cycle, on average 28 days)

Question 2

Menstrual cycle

Answer 2

Oestrogen stimulates ovulation and progesterone stimulates womb lining to grow in preparation for implantation of the embryo. If fertilisation doesn’t occur, womb lining breaks down

Question 3

McClintock & Stern (1998)

Answer 3

Pheromones from 9 women at different stages of their cycles collected using a cotton pad under the armpit rubbed on the upper lip of 20 other women. Pre-ovulation secretions made cycles shorter and post-ovulation secretions made cycles longer

Question 4

Seasonal affective disorder (SAD)

Answer 4

A depressive disorder with a seasonal pattern of onset. Lack of light prolongs melatonin secretion and reduces serotonin production

Question 5

Strengths of Infradian rhythms

Answer 5

• Influence of exogenous zeitgebers (eg. Reinberg examined woman who spent 3 months in dark cave with lamp cycle shortened from 28 days to 25.7)
• Supportive evidence for role of melatonin (eg. Terman found SAD affects 10% of people in northern US, 2% in southern Florida)

Question 6

Limitations of Infradian rhythms

Answer 6

• Methodological concerns (eg. Lack of control over confounding variables like stress and physical activity, reducing internal validity)
• Lack of success in SAD treatment (eg. Rohan found 46% relapse rate in light therapy, 27% in CBT. Glottal found no significant change in light therapy but 74% improvement if took vitamin D)