Infradian rhythms

What is an infradian rhythm?

Biological rhythm that takes more than 24 hours to complete 1 cycle

What is a

Biological rhythm that takes more than 24 hours to complete 1 cycle

Infradian rhythm

2 examples of infradian rhythm

Menstrual cycle

SAD

Average menstrual cycle length

28 days

What do oestrogen and progesterone do in menstrual cycle?

Higher oestrogen levels = cause ovulation

Progesterone = thickens womb lining after ovulation

2 things that regulate menstrual cycle

EP and EZ of light and odours

Who showed that EZ such as other women’s cycle effects menstrual cycle?

Stern + McClintock (1988)

What did Stern + McClintock (1988) do?

Showed that EZ such as other women’s cycles can effect menstrual cycles

Stern + McClintock (1988) method (3)

-29 Ps with history of irregular periods

-Samples of pheromones collected from 9 Ps at different stages of menstrual cycle (via a cotton pad placed in armpit for 8 hours)

-Pads rubbed on upper lip of other Ps

Ps in Stern + McClintock (1988)

29 women with history of irregular periods

How were pheromones gathered Stern + Mcclintock (1988)?

Cotton pad under armpit of 9 Ps in diff stages of menstrual cycle

Rubbed on upper lip of other Ps

Stern + McClintock (1988) findings

-68% of women experienced change in cycle that brought them closer to odour donor

-Latter half of cycle: cycle shortened

Beginning of cycle: cycle lengthened

How many women experienced a change in cycle that brought them closer to odour donor in Stern + McClintock (1988)?

68%

68% of women

experienced a change in cycle that brought them closer to odour donor in Stern + McClintock (1988)

3 studies on infradian rhythms

Stern + McClintock (1988)

Pentonville-Volk (1999)

Reinberg (1967)

What is

Stern + McClintock (1988)

Pentonville-Volk (1999)

Reinberg (1967)

3 studies on infradian rhythms

Is there an evolutionary advantage for synced menstrual cycles?

Yes

Shared childcare

What is SAD?

Seasonal Affective Disorder

Depressive disorder w/ a seasonal pattern of onset

Recognised by DSM-5

Main symptoms of SAD

Low mood

General lack of activity + interest in life

What do psychologists hypothesise is part of cause of SAD?

Melatonin

Winter = darker for longer so pineal gland secretes melatonin for longer

Knock on effect on production of serotonin

Why do psychologists hypothesise melatonin causes SAD?

Winter = darker for longer so pineal gland secretes melatonin for longer

Knock on effect on production of serotonin

What triggers SAD symptoms?

No. of daylight hours become shorter

Evidence for melatonin causing SAD

Terman (1988) found higher rates of SAD in northern countries

3 limitations of Ultradian + infradian cycles

-Validity of evolutionary basis of menstrual cycle questioned

-Methodological limitations in synchronisation studies

-Sleep cycle studies ignore individual differences

Limitation of ultradian and infradian rhythms - Sleep cycle studies ignores individual differences

P: Sleep cycle studies ignores individual differences

E: Study in a controlled lab setting (so can only attribute results to biological differences) showed significant differences in duration of NREM stages

C: Should focus on individual differences when doing sleep cycle studies

Limitation of ultradian and infradian rhythms - Methodological limitations in synchronisation studies

P: Methodological limitations in synchronisation studies

E: Too many other factors effect cycles eg: stress, age, exercise, that would act as confounding variables

C: Patterns of synchronisation see in Stern + McClintock (1988) no more than what would’ve occurred by chance

Limitation of ultradian and infradian rhythms - Validity of evolutionary basis of menstrual cycle questioned

P: Validity of evolutionary basis of menstrual cycle questioned

E: Researcher argued if too many females cycled tigether in a social group, would produce too much competition for highest quality male

C: Suggests avoidance of synchrony would actually be most advantageous strategy

Strength of ultradian + infradian rhythms

Research into SAD has practical applications

Strength of ultradian + infradian rhythms - Research into SAD has practical applications

P: Research into SAD has practical applications

E: Effective treatment for SAD is phototherapy (light box that stimulates light to reset melatonin levels). 60% effective but placebo effect of 30%

C: Casts doubt on chemical influence of phototherapy

Phototherapy 60% effective for SAD but

30% placebo effect