✓ Infradian Rhythms (AO1)

Question 1

What is an infradian rhythm?

Answer 1

an infradian rhythm is a biological rhythm that lasts longer than 24 hours, but less than a year

infradian rhythms can be weekly, monthly, or annually

Question 2

What are two examples of infradian rhythms?

Answer 2

the menstrual cycle - last on avg. 28 days

seasonal affective disorder - circannual (yearly)

Question 3

How does the menstrual cycle work?

Answer 3

levels of oestrogen cause the ovaries to develop an egg & release it (ovulation)

then progesterone causes the womb lining to thicken, ready for pregnancy

if pregnancy doesn’t occur, the egg is absorbed into the body & the womb lining leaves the body (menstrual flow)

Question 4

What gland coordinates the hormones for the menstrual cycle?

Answer 4

the hormones are all coordinated by the pineal gland which may be influenced by light levels
(pineal gland & melatonin may modify the pituitary release of LH & FSH)

Question 5

McClintock & Stern’s study?

Answer 5

10 year longitudinal study

29 women w a history of irregular periods

samples gathered from 9/29 then rubbed daily on the upper lip of the other 20 women

68% women’s cycles synchronised to the donor’s

Question 5

What 2 studies support the menstrual cycle as an infradian rhythm?

Answer 5

McClintock & Stern
Reinberg

Question 6

Reinberg’s study?

Answer 6

woman spent 3 months in a cave w dim light

menstrual cycle shortened to 25.7 days & took a year to return to normal once out of the cave
(supports EZ for the menstrual cycle)

Question 7

What is Seasonal Affective Disorder?

Answer 7

diagnosed as a mental disorder in the DSM-5 manual
- form of depression w persistent low mood & lack of activity
- “winter blues” occurs in late autumn/winter

circannual rhythm (yearly)

Question 8

What is the EZ & EP of SAD?

Answer 8

EZ (external cue)- shorter daylight hours in Winter
EP (internal clock) - pineal gland secretes melatonin at night so is active for longer

(increases sleepiness which lowers serotonin levels & leads to depression)

Question 9

Which study supports SAD as an infradian rhythm?

Answer 9

Terman et al

Question 10

Terman et al’s study?

Answer 10

Terman found that the rate of S.A.D is more common in New Hampshire (North US) w roughly 10% of ppl
vs.
only 2% of Florida (South US)

shows how light (EZ) affects S.A.D