Infradian Rhythms Flashcards
Outline the menstrual cycle as an infradian rhythm
Governed by monthly changes in hormone levels which regulate ovulation
Cycle = time between 1st day of period to day before next period (approx. 28 days)
Rising levels of oestrogen cause ovary to develop egg & release it (ovulation)
After ovulation, progesterone helps womb lining grow thicker, readying womb for pregnancy
No pregnancy = egg absorbed into body, womb lining comes away & leaves body (menstrual flow)
CRANG
Outline research into the synchronisation of menstrual cycles
Although menstrual cycle = endogenous system, evidence suggests influenced by exogenous factors:
Stern & McClintock (1998) studied 29 women with history of irregular periods
Samples of pheromones gathered from 9/29 at different stages of cycles
Collected by cotton pad in armpit, worn for 8 hrs
Pads treated with alcohol & frozen, rubbed on upper lip of other parties
Day 1: pads from start of cycle applied to 20, day 2: second day, etc.
Found 68% of women xp cycle changes bringing them closer to ‘odour donor’ cycle
Outline seasonal affective disorder (SAD)
Depressive disorder, has seasonal onset pattern & described & diagnosed as mental disorder in DSM-5
Symptoms = Persistent low mood alongside general lack of activity & interest in life
SAD = Particular type of infradian rhythm - Circannual rhythm as it’s yearly cycle
But can be circadian rhythm as xp of SAD may be due to disruption of S/W cycle due to prolonged periods of daily darkness during winter
Psychologists hypothesise hormone melatonin implicated in cause of SAD
During night, pineal gland secretes melanin until dawn when light ⬆️
During winter, lack of light in morning means secretion process continues for longer
Knock-on effect on production of serotonin in brain - linked to onset of depressive symptoms
Outline ultradian rhythms
Example = stages of sleep
Psychologists identified 5 distinct stages lasting for 90 minutes altogether, continuing cyclically throughout night
Stages characterised by level of brainwave activity - monitored by EEG
Stage 1&2 - Light Sleep where person easily woken - S1: Brain waves high freq & short amplitude//S2: Alpha waves continue but occasional changes in sleep spindles
Stage 3&4 - Deep sleep difficult to wake - Brain waves = Delta waves, low freq & high amplitude
Stage 5 - REM Sleep - Body is paralysed yet brain activity closely resembles awake brain
Brain produces theta waves & REM, dreams occur here or deep sleep
Evaluate menstrual synchrony research
Strength - EVOLUTIONARY BASIS - explained by natural selection
E.g. - May have been advantageous for ancestors for women to menstruate together & become pregnant at same time. In social group, this allows babies who’d lost mums after birth to access breast milk, thus improving changes of surviving
Ex. - Suggests synchronisation = adaptive strategy
Limitation - METHODOLOGICAL LIMITATIONS
E.g. - Many factors may effect change to cycle, like stress, diet, exercise, etc. These may be confounding variables - any supposed pattern of synchronisation no more than chance. Explains why other studies (Trevathan 1993) failed to replicate findings
Ex. - Suggests menstrual synchrony studies flawed
Evaluate research into ultradian rhythms
Strength - IMPROVED UNDERSTANDING - in age-related changes in sleep
E.g. - Sleep scientists observe SWC reduces with age. Growth hormone mostly produced in SWC, thus reduced in OAPs. Van Cauter (2000), resulting sleep deficit may explain issues in old age, like reduced alertness. To increase SWC, relaxation & medication may be used
Ex. - Suggests knowledge of ultradian rhythms has practical value
Limitation - INDIVIDUAL DIFFERENCES
E.g. - Tucker et al. (2007) found large differences between parties in duration of sleep in each stage, particularly 3&4. Tucker suggest these differences likely to be bio determined
Ex. - Difficult to describe ‘normal sleep’ in any meaningful way
