Lesson 8 Flashcards
What is a biological rhythms?
distinct patterns of change in a body activity that conforms to cyclical time periods. Biological rhythms are influenced by internal body clocks (endogenous pacemakers) as well as external changes to the environment (exogenous zeitgebers).
What is infradian rhythms?
A type of biological rhythm which has a duration of over 24 hours, may be weekly, monthly or annually.
infradian rhythms include the female menstrual cycle (monthly cycles) and seasonal affective disorder (SAD).
The menstrual cycle
an example of infradian rhythm. it is governed by monthly changes in hormone levels which regulates ovulation.
the menstrual cycle lasts approx 28. days from the first day of a period to the day before the next period.
regulated by hormones (endogenous pacemaker):
1. oestrogen increases to cause the ovary to develop an egg and release it (ovulation).
2. progesterone thickens the womb lining which prepares the uterus for pregnancy.
Stern and Mclintock 1998
aim - to investigate whether exogenous zeitgebers can influence the menstrual cycle.
procedure - the sample consisted of 29 women who had irregular periods.
- samples of pheromones were taken from women at different stages of their menstrual cycle, via a cotton pad placed in their armpit which were worn for 8 hours.
the pads were sterilized and rubbed on the upper lip of other women.
- on day one, pads from the start of the menstrual cycle were applied to all 20 women on day two they were given the pad from the second day of the cycle and so on.
findings - 68% of women experienced changes to their cycle which brought them closer to the cycle of their ‘odor donor’. - This suggests exogenous zeitgeber e.g. the cycle of other women can lead to menstruation synchronization.
Seasonal affective disorder (SAD)
- forms of depression (aka the winter blues)
- symptoms are triggered during the winter months - reduced daylight hours.
- symptoms include persistent low mood and low interest in activities and life.
- psychologists have hypothesised the hormone melatonin is involved in the onset of SAD.
- melatonin is secreted by the pineal gland until down where there is an increase in light.
- during winter, the lack of light means the secretion process happens for longer.
- this also influences the production of serotonin in the brain.
Ultradian rhythms
a type of biological rhythm which has a duration of less than 24 hours, such as the cycle of sleep stages that occur throughout the night.
- one of the most researched ultradian rhythms is the stages of sleep (the sleep cycle).
- five stages have been identified.
- this cycle repeats itself about every 90 - 100 minutes throughout the night.
- most of what we know about the sleep cycle comes from recording of electrical activities of the brain, with each stage showing a distinct EEG pattern.
Stages of sleep
stage 1: light sleep since we can easily be woken up from it. Sometimes we may wake without realising that we’ve even nodded off. Brain waves are slower and are called ‘theta’.
stage 2: after about a minute or so we enter stage 2. This is characterised by bursts of high frequency waves called ‘deep spindles’. We are still aware of sounds and activity around us. At this stage we are still very easily woken.
stage 3 & 4: 4-6% deep sleep begins. Brain begins to generate slow delta waves. Very deep sleep. Rhythmic breathing and limited muscle activity. Brain produces delta waves.
Stage 5: rapid eye movement. Brainwaves speed up and dreaming occurs. Muscles relax and heart rate increases. Breathing is rapid and shallow.
Evolutionary basis of the menstrual cycle
a strength of infradian rhythms is they offer supportive evolutionary explanations.
synchronisation of the menstrual cycle is thought to have some evolutionary value.
menstrual synchrony was advantageous to our ancestors because if females menstruated together, then get pregnant together, the babies would be born at a similar time and so could be cared for collectively, increasing the offspring’s chances of survival.
this suggests that menstrual synchronisation is an adaptive strategy.
Methodological limitations in synchronisation studies.
a limitation of early synchronisation studies is that there may be confounding variables involved.
for examples, many factors may influence a woman’s menstrual cycle such as stress, changes in diet, exercises etc. Additionally, the reseachers relied on the women self - reporting their menstrual cycle.
this suggests there is no guarantee that the pheromones had a direct impact on the menstrual cycle of the second woman. Furthermore, since the females engaged in self - report methods, they may not have been truthful when reporting the onset of their menstrual cycle.
as a result, the research into infradian rhythms lacks internal validity.
real life application - SAD
strength of understanding seasonal affective disorder has led to the development of treatment, for SAD this is phototherapy.
Phototherapy is a lightbox that stimulates a very strong light in the morning and evening. It is thought to reset melatonin levels in people with SAD. This relives symptoms of up to 60% of sufferers.
By having a light, this will encourage the pineal gland to stop secreting melatonin due to the increase in light, this will have a coinciding effect on increasing serotonin levels assisting the relief of symptoms.
therefore, we can improve the mood and daily functioning of individuals diagnosed with SAD, thus improving their quality of life.
individual differences
a limitation of ultradian rhythms is there is significant variation between people.
Tucker et al found large differences between participants in terms of the duration of each sleep stage, particularly stages 3 and 4.
Suggested that these differences are likely to be biologically determined.
therefore, it is difficult to describe ‘normal people’.
supporting evidence for the distinct stages of sleep
strength - supporting research on the theory of ultradian rhythms.
monitored sleep patterns of 9 adults in a sleep lab. Brainwaves were taken by an EEG and researchers controlled for alcohol and caffeine. REM was highly correlated with the experience of dreaming, brain activity varied according to how vivid dreams were, and PPs woken up during dreaming reported very accurate recall of their dreams.
The study suggests that the REM stage is a distinct place where dreaming takes place.
therefore, this increases the reliability of the REM explanation.
