Biological rhythms: infradian rhythms Flashcards
infradian rhythm definition
type of biological rhythm with a frequency of less than one cycle in 24 hours (takes more than a day) such as menstruation and seasonal affective disorder
type of brainwave in stage 1
alpha waves
type of brainwave in stage 2
alpha and sleep spindles
type of brainwave in stage 3 and 4
delta waves
type of brainwave in stage 5 (REM sleep)
theta waves
what type of biological rhythm is the menstrual cycle
infradian rhythm
what is menstrual cycle governed by
monthly changes in hormone levels which regulate ovulation
what does the menstrual cycle refer to
time between the first day of a period (when womb lining is shed) to the day before the next period
how long does menstrual cycle take
typically 28 days (but form 24-35 days is considered normal)
what happens during the menstrual cycle
rising levels of the hormone oestrogen causes the ovary to develop an egg and release it (ovulation). after ovulation the hormone progesterone helps the womb lining to grow thicker which causes the womb to be ready for pregnancy which is does not occur, the egg is absorbed into the body, the womb lining comes away and leaves the body (menstrual flow)
is the menstrual cycle endogenous or exogenous
endogenous system but can be influenced by exogenous factors
what are the exogenous factors that can effect the menstrual cycle
cycles of other women –> pheromones
Stern and McClintock study
how menstrual cycles may synchronise as a result of the influence of pheromones
when did Stern and McClintock research
1998
Stern and McClintock sample
29 women with a history of irregular periods
Stern and McClintock procedure
-29 women with history of irregular periods
-samples of pheromones were gathered from 9 women at different stages of the menstrual cycle, via cotton pads placed under their armpit
-pads were worn for at least 8 hours to endure that pheromones had been picked up
-pads were treated with alcohol and frozen
-pads were rubbed on the upper lip of the other 20 participants
-on day 1 pads from the start of the menstural cycle were applied to the 20 women, on day 2 they were given pads from day 2 etc..
Stern and McClintock findings
68% of women experienced changes to their cycle which bought them closer to the cycle of their odour donor
what is seasonal affective disorder (SAD)
depressive disorder which has a seasonal pattern of onset. categorised as a mental disorder in the DSM-5
main symptoms of SAD
as with other forms of depression its symptoms are persistent low moods alongside a general lack of activity and interest in life
what is SAD often referred to
winter blues as the symptoms are triggered during the winter months
why is SAD in the winter months
number of daylight hours becomes shorter
what type of infradian rhythm is SAD and why
circannual rhythm as is subject to a yearly cycle. can also be classed as a circadian rhythm as the experience of SAD may be due to disruption to sleep/wake cycle and this can be attributed to prolonged periods of daily darkness during winter
what hormone have psychologists hypothesised is involved in SAD
melatonin
how is melatonin involved in SAD
at night, the pineal gland recreated melatonin until dawn when there is an increase in light. during winter, the lack of light in the morning means melatonin is secreted for longer. this has a knock-on effect on the production of serotonin in the brain which has been linked to depressive symptoms
strength of infradian rhythms - evolutionary basis
-menstrual synchrony research can be explained by natural selection
-synchronisation of the menstrual cycle such as observed by Stern and McClintock has some evolutionary value. for example, for distant ancestors it may have been advantageous to be pregnant at the same time. in a social group, babies who had lost their mothers during or after childbirth to have access to breast milk and improve their chance of survival –> suggests synchronisation is an adaptive strategy
limitation of infradian rhythms - methodological limitations
-limitation of synchronisation studies is their methodological shortcomings
-many factors that may effect change to the menstrual cycle such as stress, change in diet, exercise. these may act as confounding variables which means that an supposed pattern of synchronisation is no more than would have been expected to occur by chance. this may explain why other studies (trevathan et al 1993) have failed to replicate findings–> suggets menstrual synchrony studies are flawed
evaluation of infradian rhythms - real-world application
-one of the most effective treatments for SAD is light therapy, a box which stimulated very strong light to reset the body’s internal clock. studies show this helps reduce effects of SAD in about 80% of people (Sanassi 2014). light therapy is also preferred over antidepressants to treat SAD as is regarded as safe
-however, light therapy can produce headaches and eye strain. perhaps more tellingly, Rohan et al 2009 recorded a relapse rate of 36% over successive winters, completed to 27% in group with CBT
