10/12/25, 4:10 PM Biological rhythms: Infradian
Biological rhythms: Infradian
Infradian
¬ An infradian biological rhythm is one that takes more than 24 hours to complete, for
example the menstrual cycle and seasonal affective disorder (SAD). (it might be difficult
to recall the difference between infradian and ultradian, remember infradian is linked to
SAD and menstrual cycle, but if that doesn't work then think of it meaning infrequent,
meaning it doesn't frequently occur, only every 28 days, or a year or so)
Menstrual cycle
¬ the female menstrual cycle is between the first day of a woman's period (when womb
lining is shed) to the day before the next period ~ 28 days, with a 6 day fertility period
- Increase in hormone oestrogen causes the ovary to develop an egg and release it in a
process called ovulation
- After ovulation, the hormone progesterone helps the womb lining grow thicker which
readies the body for pregnancy
- If pregnancy does not occur, the egg is reabsorbed and the womb lining is shed
(causes the menstrual flow i.e. blood)
Although it is mostly thought that the menstrual cycle is largely governed by
endogenous pacemakers, bodily clocks, other psychologists have found some
exogenous zeitgebers involved such as light and odours.
Stern and McClintock
McClintock (only him) observed women in university dormitories and found that women
appeared to synchronise their cycles with their friendship groups.
Stern and McClintock then conducted an experiment to investigate if synchronisation
was due to women sharing pheromones (a chemical released by a person that triggers
a social response in the same species, in a way it means allows for communication).
McClintock studied 29 women with irregular periods. 9 of the women would be given
cotton pads to wear under their armpits for 8 hours at different stages in their menstrual
https://app.vaia.com/studyset/17951934/summary/71354478/edit 1/3
Biological rhythms: Infradian
Infradian
¬ An infradian biological rhythm is one that takes more than 24 hours to complete, for
example the menstrual cycle and seasonal affective disorder (SAD). (it might be difficult
to recall the difference between infradian and ultradian, remember infradian is linked to
SAD and menstrual cycle, but if that doesn't work then think of it meaning infrequent,
meaning it doesn't frequently occur, only every 28 days, or a year or so)
Menstrual cycle
¬ the female menstrual cycle is between the first day of a woman's period (when womb
lining is shed) to the day before the next period ~ 28 days, with a 6 day fertility period
- Increase in hormone oestrogen causes the ovary to develop an egg and release it in a
process called ovulation
- After ovulation, the hormone progesterone helps the womb lining grow thicker which
readies the body for pregnancy
- If pregnancy does not occur, the egg is reabsorbed and the womb lining is shed
(causes the menstrual flow i.e. blood)
Although it is mostly thought that the menstrual cycle is largely governed by
endogenous pacemakers, bodily clocks, other psychologists have found some
exogenous zeitgebers involved such as light and odours.
Stern and McClintock
McClintock (only him) observed women in university dormitories and found that women
appeared to synchronise their cycles with their friendship groups.
Stern and McClintock then conducted an experiment to investigate if synchronisation
was due to women sharing pheromones (a chemical released by a person that triggers
a social response in the same species, in a way it means allows for communication).
McClintock studied 29 women with irregular periods. 9 of the women would be given
cotton pads to wear under their armpits for 8 hours at different stages in their menstrual
https://app.vaia.com/studyset/17951934/summary/71354478/edit 1/3
