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What are biological rhythms?
Biological rhythms are distinct patterns of changes in body activity that conform to cyclical time periods
What are biological rhythms influenced by?
Influenced by internal body clocks (endogenous pacemakers), as well as external changes to the environment (exogenous zeitgebers)
What is the circadian rhythm?
A pattern of behaviour that occurs or recurs approximately every 24-hours which is set and re-set by environmental light levels
e.g. 4am = lowest body temperature
6:45 = sharpest blood pressure rise
14:30 = best coordination
What are some examples of circadian rhythms?
sleep-wake cycle
body temperature
hormone production
How does light affect the circadian rhythm?
light provides the primary input to this system
light is first detected by the eye which then sends messages (in relation to brightness) to the suprachiasmatic nuclei (SCN)
the SCN then uses this information to coordinate the activity of the entire circadian rhythm
What is the sleep-wake cycle?
a circadian rhythm that dictates when humans should be asleep and awake
light and dark are the external signals (exogenous zeitgebers) determining when we feel the need to sleep and the need to wake
the sleep-wake cycle is determined by both the circadian rhythm but also by homeostasis
What is core body temperature?
an example of a circadian rhythm
itās at its lowest at 4am - 36 degrees
itās at its highest at 7pm - 38 degrees
What is hormone production?
hormone release follows a circadian rhythm too
e.g. release of melatonin
melatonin comes from the pineal gland in the brain
peak levels of hormones occurring during the hours of darkness
so when it is dark, more melatonin is produced and when itās light again, the production of melatonin decreases and the person wakes
How does homeostasis affect our circadian rhythms?
homeostasis is a self-regulating process by which biological systems maintain stability while adjusting to changing external conditions
sleep and wakefulness isnāt only determined by your circadian rhythm
if you have been awake for a long time, your homeostasis tells us that the need for sleep is increasing due to the amount of energy being used up throughout wakefulness
this homeostatic drive for sleep increases throughout the day, reaching its maximum in late evening when people finally fall asleep
How does the circadian rhythm and homeostasis affect our need for sleep?
circadian rhythm keeps us awake as long as there is daylight and prompts us to sleep when it is dark
the homeostatic system makes us sleepier as time goes on throughout the waking period - regardless of it being day or night
What is free-running?
our internal circadian clock is described as free-running
its intolerant of major alterations e.g. change of time zone
this makes the biological clock become out of balance
Michael Siffre Case Ctudy
Duration: 2 months
Location: Southern Alps
Year: 1962
Date he resurfaced: 17th September
Date he thought it was: 20th August
his free running biological rhythm changed to 25 hours
Aschoff and Wever (1976)
4 weeks in a WW1 bunker deprived of natural light
all but one displayed a natural sleep/wake cycle of between 24 and 25 hours
both Siffres research and the Bunker study suggests that the natural sleep wake cycle may be slightly longer than 24 hours
however, we train ourselves by exogenous zeitgebers associated with the 24 hour day
Simon Folkard et al (1985)
studied the influence of environment cues on our internal biological clock
12 people living in a dark cave for 3 hours
went to bed when the clock said 11:45 and out of bed at 7:45
over the course of the study, the researchers sped up the clocks so an apparent day lasted only 22 hours (unknown to the participants)
only one participant was able to comfortably adjust to the new regime
suggests the existence of a strong āfree runningā circadian rhythm that cannot be easily overridden by changes in the external environment
AO3 - research support
P = there is research support for circadian rhythms
EX = this includes the effect of external cues like light on this system
EV = Siffre (1975) found that the absence of external cues significantly altered his circadian rhythm: when he returned from an underground stay with no clocks or light he believed the date to be a month earlier than it was
C = In addition, FolkardĀ et al (1985) studies the influence of environmental cues on our internal biological clock. 12 people, living in a dark cave for 3 weeks and went to bed when the clock said 11:45 out of bed at 07:45. Over the course of the study, unbeknown to the participants, the researchers sped up the clock so an apparent DAY lasted only 22 hours. Only one participant was able to comfortably adjust to the new regime- suggesting the others found it difficult to adjust to a shorter day.Ā
LB = this suggests that Siffreās 24 hour sleep-wake cycle was increased by the lack of external cues, known as exogenous zeitgebers
A)3 - use of case studies
P = studies of the sleep-wake cycle tend to involve small groups of participants
EX = this is ideographic research and difficult to generalise
EV = Aschoff and Wever (1976) studies a small sample of participants who spent 4 weeks in a WW1 bunker deprived of natural light. All but one displayed a natural sleep wake cycle of between 24 and 25 hours. Both Siffres research and the Bunker suggest that the āNaturalā sleep wake cycle may be slightly longer than 24 hours but is entrained by exogenous zeitgebers associated with the 24 hours day.
C = however, it is important to note the differences between individuals when it comes to circadian cycles. Duffy et al (2001) found that āmorning peopleā prefer to rise and go to bed early (6am - 10pm) whereas āevening peopleā prefer to wake up and go to bed later (10am - 1am). This demonstrates that there may be innate individual differences in circadian rhythm, which suggests that researchers should focus on these differences during investigations
LB = this suggests that individual cycles can vary. There are also age differences in sleep cycles as teenagers circadian rhythms begin 2 hours after adults which means findings should not be generalised.
AO3 - temperature
P = additionally, it has been suggested that temperature may be more important than light in determining circadian rhythms
EV = Buhr et al (2010) found that fluctuations in temperature set the timing of cells in the body and caused tissues and organs to become active or inactive. Buhr claimed that information about light levels is transformed into neural messages that set the bodyās temperature
EX = body temperature fluctuates on a 24-hour circadian rhythm and even small changes in it can send a powerful signal to our body clocks
EXT = furthermore, the idea that all human bodies work on a 24 hour cycle is biologiaclly deterministic because it assumes that hormones are the only cause of changes in circadian rhythms, evidence suggests that meal times and travelling can also cause changes to this rhythm as differences in time zones affect ānormalā routines, suggesting the influence of light is subdued
LB = this shows that circadian rhythms are controlled and affected by several different factors, and suggests that a more holistic approach to research may be preferable
What is an infradian rhythm?
A rhythm that lasts longer than 24 hours
e.g. menstrual cycle, seasonal affective disorder, hibernation/migration (in animals)
Female menstrual cycle
regulated by hormones (endogenous pacemakers)
ovulation occurs halfway through cycle, when oestrogen levels are highest
after ovulation, progesterone levels increase, ready for possible embryo implantation
a typical cycle is approx. 28 days
Stern and McClintock (1998)
āsyncing upā menstrual cycles
29 women - all with history of irregular periods
pheromone samples were gathered on cotton pads placed under the arms, from 9 women each at different stages of their menstrual cycles
they were frozen and treated with alcohol and rubbed on the top lip of the other 20 participants
day 1 = all 20 got pads from day 1 of the cycle, day 2 = pads from day 2 of the cycle etc.
McClintock found that 68% of the women experienced changes in their cycle which brought them closer to that of their āodour donorā
Seasonal Affective Disorder (SAD)
SAD is an infradian rhythm related to the season
melatonin is secreted by the pineal gland at night
longer nights = increased melatonin secretion
linked to increase in depressive symptoms
Magnussen (2000) suggested a seasonal variation in mood for humans, especially women
AO3 - support for research
P = there is evolutionary value for the menstrual cycle to be synchronised
EX = for our ancestors, it may have been advantageous for females to menstruate together. This would mean that new-borns could be cared for collectively within a social group
EV = research from Stern and McClintock (1988) found that 68% of the women experienced changes in their cycle which brought them closer to that of their āodour donorā.
C = however, Schank (2004) argued that if there were too many females cycling together within a social group, this would produce competition for the highest quality males. For this perspective it would be better to not have synchronised menstrual cycles
LB = this makes us question the validity of the evolutionary perspective as there is contradictory arguements
AO3 - criticisms in synchronisation studies
P = However, criticisms have been made of early synchronised studies and the methods employed in them.
EX = Researchers argue that there are many other factors that may effect change in a women's menstrual cycle and the exogenous zeitgebers, such as light, may be more influential than previously thought
EV = For example, Reinberg (1967) examined a woman who spent 3 months in a cave with only a small lamp to provide light. Reinberg noted that her menstrual cycle shortened from the usual 28 days to 25.7 days.
EXT = In addition to this, Stern and McClintock's experiment used a limited sample of only 29 women, as do many other experiments into Infradian rhythms. These small sample sizes prevent the results from being reliably generalised to the wider population because they are too ideographic to conclude that there is a global pattern.
LB = This result suggests that the lack of light, an exogenous zeitgeber, in the cave affected her menstrual cycle, and therefore demonstrates the effect of external factors on Infradian rhythms.
AO3 - practical application - SAD
P = There is also supporting research of the role of melatonin in SAD.
EX = Terman found that the rate of SAD is more common in Northern countries where the winter nights are longer. For example, he found that SAD affects roughly 10% of people living in New Hampshire and only 2% of residents in southern Florida.
EX = These results suggest that SAD is in part affected by light (exogenous zeitgeber) that results in increased levels of melatonin.
EXT = furthermore, a strength of this idea is that it increases our knowledge of how to treat people who suffer from SAD, for example, using phototherapy. The lightbox stimulates very strong light which is thought to reset melatonin levels, and has been found to relieve symptoms for 60% of people
LB = The research into SAD has helped relieve the symptoms of depression and improve the lives of many people suffering from low mood and fatigue.
Ultradian rhythms
ultradian rhythms last fewer than 24 hours
e.g. human sleep patterns/meal patterns - eating 3 times a day
Sleep stages
the pattern alternates between REM and NREM
REM = rapid eye movement
NREM = non-rapid eye movement
consists of 5 stages of 90 mins
a complete cycle consists of a progression through stages 1-4 and then the cycle starts all over again
most people have 5 cycles a night
using EEg (electroencephalogram) scanners to measure the electrical activities within our brains
Human sleep stages
Stage 1 = light sleep
muscle activity slows down
occasional muscle twitching
Stage 2
breathing pattern and heart rate slows
slight decrease in body temp
Stage 3 = deep sleep
brain begins to generate slow delta waves
Stage 4 = very deep sleep
rhythmic breathing
limited muscle activity
brain produces delta waves
Stage 5 = REM
brainwaves speed up and dreaming occurs
muscles relax and heart rate increases
breathing is rapid and shallow
Waves
alpha waves are associated with light sleep which progress to theta
delta waves are associated with deeper sleep
synchronised = recognisable waveform (alpha, theta and delta), often detected during sleep
desynchronised = no pattern. usually a mix of all 4. often detected when someone is awake
Meal patterns
most humans eat three meals a day and appetite rises and falls because of food consumption
AO3 - evidence for sleep stages
P = there has been a number of studies that have supported the different stages in sleep
EX = this research emphasises how brain waves vary in the stages and how brain activity can change from synchronised to desynchronised depending on the stage of sleep
EV = Dement and Kleitman (1957) monitored the sleep pattern of 9 adults using EEGās. REM activity during sleep was highly correlated with the experience of dreaming and brain activity varied according to how vivid dreams are.
C = however, whilst Dement and Kleitmanās research had high levels of control on extraneous variables, such as caffeine and alcohol intake, they used a very small sample which milits the generalisability of the study and the validity of the conclusions drawn from it
LB = nevertheless, replication of this investigation have noted similar findings which increases the validity and support for the sleep stages
AO3 - individual differences in sleep cycles
P = it should be noted that there are individual differences when it comes to the stages of sleep
EV = Tucker et al. (2007) found significant differences between participants in terms of the duration of each stage, particularly stages 3 and 4
EX = this emphasises the importance in considering external factors, such as genetics or the environmental context of an individual, as factors like a family history of insomnia or drinking coffee could affect the brain activity and wave patterns during the different stages of sleep
EXT = in addition, a case study of Randy Gardener who remained awake for 264 hours. After this experience, Randy slept for just 15 hours. The nights following the experiment he recovered 70% of stage 4 sleep, 50% of his REM sleep and very little of the other stages
LB = this demonstrates that there may be innate individual differences in ultradian rhythms and they are not as fixed as first thought. This means that it is worth focusing on these differences during investigations into sleep cycles