biopsychology Flashcards
(91 cards)
1
Q
The nervous system - key features
A
The nervous system is a specialised network of cells and our primary communication system. It is based on electrical (and chemical) signals
two main functions:
- to collect, process and respond to information in the environment
- to co-ordinate the working of different organs and cells in the body
2
Q
The structure and function of the central nervous system
A
- the CNS is made up of the brain and the spinal cord
- the brain is the centre of conscious awareness
- the outer layer of the brain, the cerebral cortex (3mm thick), is highly developed in humans and is what distinguishes our higher mental functions from those of animals
- the brain is divided into two hemispheres (right and left)
- the spinal cord is an extension of the brain and responsible for reflex actions and connects nerves to the PNS (peripheral nervous system)
3
Q
The structure and function of the PNS
A
- the PNS transmits messages, via millions of neurons, to and from the nervous system
- the PNS is further subdivided into:
- autonomic nervous system - governs vital functions in the body such as breathing, heart rate, digestion, sexual arousal and stress responses
- somatic nervous system - governs muscle movement and receives information from sensory receptors
4
Q
the endocrine system - key features
A
the endocrine system works alongside the nervous system to control vital functions in the body through the action of hormones
it works more slowly than the nervous system (seconds instead of milliseconds) but has widespread and powerful effects
5
Q
glands
A
glands are organs in the body that produce hormones
the key endocrine gland is the pituitary gland, located in the brain. it is called the ‘master gland’ because it controls the release of hormones from all the other endocrine glands in the body
6
Q
hormones
A
hormones are secreted in the bloodstream and affect any cell in the body that has a receptor for that particular hormone
for example, thyroxine produced by the thyroid grand affects cells in the heart and also cells throughout the body which increase metabolic rates. this in turn affects growth rates
7
Q
the endocrine system and the ANS work together
for example, the fight or flight response
A
Often the endocrine system and the ANS work in parallel, e.g during a stressful event
- stressor perceived by hypothalamus which activates the pituitary
- the sympathetic nervous system is now aroused
- adrenaline is released from the adrenal medulla into the bloodstream. this delivers the aroused state causing changes in target organs in the body e.g increased heart rate, dilation of pupils, decreased production of saliva. this is called the fight or flight response
- immediate and automatic - this response happens the instant a threat is perceived
- parasympathetic nervous system - (rest and digest) takes over once the threat has passed. this returns the body to its resting state. this acts as a ‘brake’ and reduces the activities of the body that were increased by the actions of the sympathetic branch
8
Q
function and types of neurons
A
Neurons provide the nervous system with its primary means of communication by transmitting signals electrically and chemically.
There are three different types:
- sensory - carry messages from the PNS to the CNS. they have long dendrites and short axons. located in the PNS in clusters called ganglia
- relay - connect sensory neurons to motor neurons or other relay neurons. they have short dendrites and short axons. of all neurons 97% are relay neurons and most are in the brain and visual system
- motor - connect the CNS to effectors such as muscles and glands. they have short dendrites and long axons. cell bodies may be in the CNS but long axons form part of CNS.
9
Q
labelled diagram of neurons
A
cell body, dendrites, axon, terminal buttons
10
Q
electrical transmission - the firing of a neuron
A
When a neuron is in a resting state the inside of the cell is negatively charged compared to the outside.
When a neuron is activated by a stimulus, the inside of the cell becomes positively charged for a split second causing an action potential to occur.
This creates an electrical impulse that travels down the axon towards the end of the neuron.
11
Q
what is a synapse
A
each neuron is separated from the next by an extremely tiny gap called the synapse
12
Q
chemical transmission - the events that occur at the synapse
A
signals within neurons are transmitted electrically, but signals between neurons are transmitted chemically across the synapse
when the electrical impulse reaches the end of the neuron (the presynaptic terminal) it triggers the release of a neurotransmitter from tiny sacs called synaptic vesicles
once a neurotransmitter crosses the gap, it is taken up by a postsynaptic receptor site on the next neuron, so the impulse only ever travels in one direction
the chemical message is converted back into an electrical impulse and the process of electrical transmission begins
13
Q
synaptic transmission - neurotransmitters (structure)
A
Chemicals that diffuse across synapse to the next neuron in the chain
Each has own specific molecular structure that fits perfectly into postsynaptic receptor site like lock and key
each has specific functions e.g:
E.g. acetylcholine: where motor neurons meet muscle, causes muscles to contract
E.g. serotonin: affect mood/social behaviour, cause of depression
14
Q
synaptic transmission - excitation and inhibition
A
-neurotransmitters have either an excitatory or inhibitory effect on neurons;
-adrenaline is excitatory, it increases the positive charge of the postsynaptic neuron making it more likely to fire
-serotonin is inhibitory, it increases the negative charge of the postsynaptic neuron making it less likely to fire
- dopamine is an unusual neurotransmitter as it is equally likely to have a excitatory or inhibitory effects on the postsynaptic neuron
15
Q
synaptic transmission - summation
A
Excitatory/inhibitory influenced summed and must reach certain threshold in order for the action potential of the postsynaptic neuron to be triggered
if Net effect of neurotransmitters is inhibitory: less likely to fire
Net effect excitatory: more likely to fire
16
Q
location of the brain - holistic theory replaced by localisation theory
A
in the early 19th century holistic theory suggested that parts of the brain were involved in processing thought and action
but specific areas of the brain were later lined with specific physical and psychological functions (localisation theory)
if an area of the brain is damaged through illness or injury, the function associated with that area is also affected
17
Q
brain is divided into two hemispheres and lateralised
A
lateralisation - some physical and psychological functions are controlled by a particular hemisphere
generally, the left side of the body is controlled by the right hemisphere, the right side of the body controlled by the left hemisphere
18
Q
outer layer of brain
A
cerebral cortex
the cerebral cortex is like a ‘tea cosy’ covering the inner parts of the brain. it is about 2mm thick and is what separates us from lower animals as it is highly developed
the cortex appears grey due to the location of cell bodies - hence the phrase ‘grey matter’
19
Q
cerebral cortex of both hemispheres is divided into four lobes (frontal, parietal, occipital, and temporal)
A
(frontal, parietal, occipital, and temporal)
motor area - at the back of the frontal lobes (both hemispheres). controls voluntary movement. damage may result in loss of control over
20
Q
motor area:
A
motor area - at the back of the frontal lobes (both hemispheres). controls voluntary movement. damage may result in loss of control over fine motor movements
21
Q
somatosensory area
A
-an area at the front of the parietal lobes
-processes sensory information from the skin (touch, heat etc)
-the amount of somatosensory area devoted to a particular body part denotes its sensitivity
22
Q
visual area
A
-in the occipital lobe at the back of the brain.
- each eye sends information from the right visual field to the left visual cortex and from the left visual field to the right visual cortex
23
Q
auditory area
A
- in the temporal lobe
- analyses speech based information
- damage may produce partial hearing loss - the more extensive the damage, the more serious the loss
24
Q
the language centres - Broca’s area (speech production)
A
identified by Broca in the 1880s, in the left frontal lobe
damage to this area causes Broca’s aphasia which is characterised by speech that is slow, laborious and lacking in fluency. Broca’s patients may have difficulty finding words and naming certain objects.
people with Broca’s aphasia have difficulty with prepositions and conjunctions
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Language Centres - Wernicke's Area
identified by wernicke in 1880s in the left temporal lobe
people with wernicke's aphasia produce language but have problems understanding it, so they produce fluent but meaningless speech (tan example)
they will often produce non sense words (neologisms) as part of the content of their speech
26
strength of localisation theory (neurosurgery)
Support from neurosurgery
Neurosurgery is used to treat mental disorders - e.g cingulotomy involves isolating cingulate gyrus - dysfunction of this can cause OCD
Dougherty studied 44 people peoplewith OCD Who had a cingulotomy - it was found that 30% met the criteria for successful response and 14% for partial response
The success of such procedures strongly suggest that behaviours associating with serious mental disorders may be localised
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another strength of localisation theory + cp (brain scan / rats)
brain scan evidence to support it
- Petersen used brain scans to show activities in wernickes area during listening task and in broca area during a reading task
-a study of LTM by Tulving revealed semantic and episodic memories are located in different parts of the prefrontal cortex,
there's now lots of sophisticated and objective methods for measuring activity in brain provides sound scientific evidence of localisation of function
- counterpoint- Lashley removed areas of the cortex (10%-50%) in rats that were learning the route through a maze. No area was proven to be more important than any other area in terms of the rats' ability to learn the route. The process of learning seemed to require every part of the cortex rather than being confined
This suggests that higher cognitive processes, such as learning, are not localised but distributed in a more holistic way in the brain.
28
limitation of localisation theory (model questioned)
- the language localisation model has been questions
Dick and Tremblay (2016) found that very few researchers still believe language is only in Broca's and Wernicke's area
advanced techniques (e.g fMRI) have identified regions in the right hemisphere and the thalamus
this suggests that, rather than being confined to a couple of key areas, language may be organised more holistically in the brain, which contradicts localisation theory
29
Hemispheric lateralisation
The brain is lateralised i.e. two sides (hemispheres).
30
Localised
Some functions are localised and appear in both left and right hemispheres (LH and RH).
e.g. auditory, visual, motor, somatosensory areas.
31
Localised and lateralised
Two main language centres are in the LH (for most people) - Broca's area (left frontal lobe), Wernicke's area (left temporal lobe).
RH produces limited words but provides emotional context. LH may be the analyser, RH the synthesiser.
32
Contralateral
In the motor area, the right hemisphere controls the left side of the body and vice versa (cross-wired).
33
Contralateral and ipsilateral
Left visual field (LVF) of both eyes is connected to the
RH and right visual field (RVF) of both eyes is connected to the LH.
Enables the visual areas to compare the slightly different perspective from each eye and aids depth perception.
Same arrangement for auditory areas.
34
Sperry (1968) Split-brain research procedure
'Split-brain' = two hemispheres surgically separated by cutting the
connections e.g. the corpus callosum.
Used to treat severe epilepsy to reduce the 'electrical storm' across hemispheres.
PROCEDURE
Eleven split-brain participants were studied using the set-up shown on the left. Image or word projected to RVF (processed by LH), and same, or different, image could be projected to the LVF (processed by RH).
Presenting the image to one hemisphere meant that the information could not be conveyed from that hemisphere to the other.
35
Sperry (1968) Split-brain research: conclusions
Object shown to RVF: (right visual field)
• Participant can describe what is seen (language centres in LH).
Object shown to LVF: (left visual field)
Cannot name object (no language centres in RH).
Can select matching object behind screen using left hand.
Can select object closely associated with picture (e.g. ashtray if picture of cigarette).
Pinup picture shown to LVF, participant giggled but reported seeing nothing.
Demonstrates how certain functions are lateralised in the brain, shows that LH is verbal and the RH is 'silent' but emotional.
36
Strength of hemispheric lateralisation (normal brains)
- evidence of lateralised brain functions in 'normal brains'
pet scans show when 'normal' participants attend to global elements of an image, the RH is more active
when requires to focus on finer detail the specific areas of the LH tend to dominate (Fink et al 1996)
This suggests that hemispheric lateralisation is a feature of the normal brain as well as the split brain
37
Limitation of hemispheric lateralisation (analysed vs synthesiser)
- the idea of analysed versus synthesiser brain may be wrong
There may be different functions in the RH and LH but research suggests people do not have a dominant side, creating a different personality
Nielsen et al (2013) analysed 1000 brain scans, finding people did use certain hemispheres for certain tasks but no dominance
this suggests that the notion of right or left brained people is wrong e.g artist' brain
38
Another strength of hemispheric lateralisation (recent studies)
- support from more recent split brain studies
Luck et al (1989) showed that split brain participants are better than normal controls e.g twice as fast at identifying the odd one out in an array of similar objects
in the normal brain, the LH's superior processing abilities are 'watered down' by the inferior right hemisphere
this supports Sperry's earlier findings that the left brain and right brain are distinct in terms of functions and abilities
39
Another limitation of hemispheric lateralisation (epilepsy)
- casual relationships are hard to establish
In Sperry's research the behaviour of the split brain participants was compared to a neurotypical control group
however, none of the control group had epilepsy. Any differences between the groups may be due to epilepsy not the split brain (a confounding variable)
this means that some of the unique features of the split brain participants' cognitive abilities might have been due to their epilepsy
40
Plasticity - The brain is 'plastic'
- synaptic connections form and are pruned
During infancy, the brain experiences a rapid growth in synaptic connections, peaking at about 15,000 at age 2-3 years (Gopnik et al. 1999).
As we age, rarely-used connections are deleted and frequently-used connections are strengthened - synaptic pruning.
It was once thought these changes were limited to childhood.
But recent research suggests neural connections can change or be formed at any time, due to learning and experience.
41
The concept of plasticity is supported by a taxi driver study.
Maguire et al. (2000) found significantly more volume of grey matter in the posterior hippocampus in London taxi drivers than in a matched control group. This part of the brain is linked with the development of spatial and navigational skills.
As part of their training, London cabbies take a complex test called 'The Knowledge' to assess their recall of city streets and possible routes. This learning experience appears to alter the structure of the taxi drivers' brains! The longer they had been in the job, the more pronounced was the structural
difference.
42
Plasticity is also supported by research on learning
Draganski et al. (2006) imaged the brains of medical students
three months before and after final exams. Learning-induced changes were seen in the posterior hippocampus and the parietal cortex, presumably as a result of learning for the exam.
43
Functional recovery of the brain after trauma- Following trauma unaffected areas of the brain take over lost functions.
Functional recovery of the brain after trauma is an important example of neural plasticity - healthy brain areas take over functions of areas damaged, destroyed or even missing.
Neuroscientists suggest this process occurs quickly after trauma (spontaneous recovery) and then slows down - at which point the person may require rehabilitative therapy.
44
The brain
'rewires' itself
by forming
new synaptic connections.
The brain is able to rewire and reorganise itself by forming new synaptic connections close to the area of damage.
Secondary neural pathways that would not typically be used to carry out certain functions are activated or 'unmasked' to enable functioning to continue.
45
Structural
changes in the brain after trauma
Further structural changes may include:
Axonal sprouting - growth of new nerve endings which connect with other undamaged cells to form new neuronal pathways.
Denervation supersensitivity - axons that do a similar iob become aroused to a higher level to compensate for the ones that are lost.
Recruitment of homologous (similar) areas - the opposite side of the brain takes over specific tasks e.g. language production.
46
Strength of plasticity (age)
May not decline sharply with age -
Bozzola et al demonstrated how 40 hours of golf training produced changes in neural representations in participants aged 40-60,
using fMRIs motor cortex activities in novice golfers increased compared to a control group suggesting positive effects after training,
this shows that neural plasticity can continue throughout the lifespan
47
Limitation of plasticity (negative consequences)
- possible negative behavioural consequences
the brains adaptation to prolonged drug use leads to poorer cognitive functioning in later life, as well as increased risk of dementia (Medina at al 2007)
60-80% of amputees have phantom limb syndrome (experience sensations in missing limb due to changes in somatosensory cortex)
this suggests that the brains ability to adapt to damage is not always beneficial and may lead to physical and psychological problems
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strength of functional recovery (real world application)
Real-world application -
understanding plasticity led to neurorehabilitation understanding axonal growth encourages new therapies
for example constraint induced movement therapy involves massed practice with an affected arm while unaffected arm is restrained,
this shows research into functional recovery helps medical professional know when interventions can be made.
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Limitation of functional recovery (cognitive reserve)
- neural plasticity may be related to cognitive reserve
Schneider et al 2014 looked at the time brain injury patients had spend in education (indicated their cognitive reserve) and their chances of a disability free recovery (DFR)
40% of patients who achieved DFR had more than 16 years' education compared to about 10% of patients who had less than 12 years' education
this suggests that cognitive reserve is a crucial factor in determine how well the brain adapts after trauma
50
Scanning and other techniques- Psychologists use medical techniques to investigate brain localisation.
Techniques for investigating the brain are often used
Psychologists use medical techniques to investigate brain localisation.
for medical purposes in the diagnosis of illness.
The purpose of scanning in psychological research is often to investigate localisation - to determine which parts of the brain do what.
51
fMRI - highlights active areas of the brain
Functional magnetic resonance imaging (fMRI)
detects changes in both blood oxygenation and flow that occur due to neural activity in specific brain areas.
When a brain area is more active it consumes more oxygen and blood flow is directed to the active area (haemodynamic response).
fMRI produces a 3D image showing which parts of the brain are active and therefore must be involved in particular mental processes.
52
EEG
shows overall electrical activity
Electroencephalogram (EEG) measures electrical
Shows overall electrical activity within the brain via electrodes using a
skull cap (looks a bit like a swimming cap with the electrodes attached).
The scan recording represents the brainwave patterns generated from thousands of neurons. This shows overall brain activity.
EEG is often used as a diagnostic tool. For example unusual arrhythmic patterns of brain activity may indicate abnormalities such as epilepsy, tumours or sleep disorders.
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ERP's - brainwaves related to particular events
Event-related potentials (ERPs) are what is left when all extraneous brain activity from an EEG recording is filtered out.
This is done using a statistical technique, leaving only those responses that relate to the presentation of a specific stimulus (for example).
ERPs are types of brainwave that are triggered by particular events.
Research has revealed many different forms of ERP and how these are linked to cognitive processes (e.g. perception and attention).
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Post mortem examinations
A technique involving the analysis of a person's brain following their death.
Areas of the brain are examined to establish the likely cause of a deficit or disorder that the person experienced in life.
This may also involve comparison with a neurotypical brain in order to assess the extent of the difference.
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Strengths of fMRI
- it is risk free and high spatial resolution
unlike other scanning techniques such as PET, it does not rely on the use of radiation and is safe If used correctly it is virtually risk-free, non-invasive and straightforward to use
it also produces images that have very high spatial resolution, showing detail by the millimetre
this means fMRI can safely provide a clear picture of how brain activity is localised
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Limitations of fMRI
- it is expensive and poor temporal resolution
fMRI is expensive compared to other techniques
it has poor temporal resolution because of the 5 second lag between initial neural activity and image
this means fMRI may not truly represent moment to moment brain activity
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strengths of EEG
- are practical and uses high temporal resolution
EEG has contributed to our understanding of the stages of sleep
it has high temporal resolution - brain activity in one millisecond
this shows the real world usefulness of the technique
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Limitations of EEG
-information is generalised and source not pinpointed
the EEG produces a generalised signal from thousands of neurons
it is difficult to know the exact source of neural activity
therefore EEG can't distinguish the activity of different but adjacent neurons
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Strengths of ERP
-specificity and good temporal resolution
measures of neural processes more specific with ERPs than EEGs
ERPs have excellent temporal resolution, better than fMRI
this means that ERPs are frequently used in cognitive research
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Limitations of ERPs
-lack of standardisation and background 'noise'
lack of standardisation makes it diffuse to confirm findings in studies involving ERPs
background 'noise' and extraneous material must be completely eliminated
these issues are a problem because they may not always be easy to achieve
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Strengths of post mortems
-localisation and medical research
broca and wernicke both relied on post mortem studies
used to link HM's memory deficits to damage in his brain
this means they continue to provide useful information
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Limitations of post mortems
- knowing causation and ethics
observer damage in the brain may not be linked to the deficits under review
post mortem studies raise ethical issues of consent after death (eg HM)
this challenges their usefulness in psychological research
63
Circadian rhythms (about one cycle every 24 hours) - Biological rhythms governed by endogenous pacemakers and exogenous zeitgebers.
Biological rhythms are periodic activity, governed by:
Internal biological 'clocks* (endogenous pacemakers).
External changes in the environment (exogenous zeitgebers).
Some of these rhythms occur many times a day (ultradian rhythms). Others take more than a day to complete (infradian rhythms).
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The circadian rhythm lasts for about 24 hours.
Circa meaning 'about' and diem meaning 'day'
There are several important types of circadian rhythm such as the sleep/wake cycle
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Sleep/wake cycle governed by internal and external mechanisms.
Exogenous zeitgebers - the fact we feel drowsy when it's night-time and alert during the day shows the effect of daylight.
Endogenous pacemakers - a biological clock left to its own devices' without the influence of external stimuli (e.g. light)
is called 'free-running.
The basic rhythm is governed by the suprachiasmatic nucleus (SCN). The SCN lies just above the optic chiasm which provides information from the eyes about light.
Exogenous zeitgebers (light) can reset the SC
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Siffre demonstrated a free running circadian rhythm of about 25 hours
French caver Siffre spent long periods in dark caves to
demonstrated examine the effects of free-running biological rhythms - a free-running two months (in 1962) and six months (in the 1970s).
In each case study, Siffre's free-running circadian rhythm settled down to about 25
Importantly, he did have a regular sleep/wake cycle.
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Aschoff and
Wever also found a similar circadian rhythm.
A group of participants spent four weeks in a World War 2 bunker deprived of natural light (Aschoff and Wever 1976).
All but one (whose sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24 and 25 hours.
Siffre's experience and the bunker study suggest that the
'natural' sleep/wake cycle may be slightly longer than 24 hours but is entrained by exogenous zeitgebers associated with our 24-hour day (e.g. daylight hours, mealtimes, etc.).
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Folkard et al.
showed endogenous pacemakers stronger than exogenous zeitgebers,
Folkard et al. (1985) studied a group of 12 people who lived in a dark cave for three weeks, going to bed when the clock said 11.45 pm and waking when it said 7.45 am.
The researchers gradually speeded up the clock (unbeknown to the participants) to a 22-hour day.
Only one participant comfortably adjusted to the new regime. This suggests the existence of a strong free-running circadian rhythm not controlled by exogenous zeitgebers.
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Strength of circadian rhythm research + CP (night shift / correlational)
-application to shift work
shift work creates desynchronisation of biological rhythms. Boivin eat al (1996) found shift workers experience a lapse of concentration around 6am (a circadian trough) so accident are more likely
research also suggests a link between shift work and poor health, with shift workers three times more likely to develop heart disease
thus, research into the sleep/wake cycle may have economic implications in terms of how best to manage shift work
CP: the research is correlational, therefore desynchronisation may not be the cause of observed difficulties. For example, Solomon (1993) concluded that high divorce rates in shift workers might be due to missing out in important family events
this suggests that it may not be biological factors that create the adverse consequences associated with shift work
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another strength of circadian rhythm research (real world application aspirin)
- real world application to medical treatment
circadian rhythms co-ordinate the body's basic possesses (e.g heart rate, hormone levels) with implications for chronotherapeutics (timing medication to maximise effects on the body)
aspirin reduces heart attacks, which are most likely in the morning. Bonten at al found taking aspirin is most effective last thing at night
this shows that circadian rhythm research can help increase the effectiveness of drug treatments
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Limitation of circadian rhythm research (generalisations)
- generalisations are difficult to make
studies of the sleep/wake cycle often use small groups (aschoff and wever) of participants or even single individuals (siffre)
particupants may not be representative of the wider population and this limits making meaningful generalisations. Siffre observed that his internal clock ticked much more slowly at 60 than when he was younger
this suggests that even when the same person is involved, there are factors that may prevent general conclusions being drawn
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Infradian rhythms (less than one cycle in 24 hours) - The female menstrual cycle is an infradian rhythm.
The human female menstrual cycle is about 28 days (i.e. less than one cycle in 24 hours - infra diem meaning
'below' a day).
Rising levels of estrogen cause the ovary to release an egg (ovulation). Then progesterone helps the womb lining to thicken, readying the womb for pregnancy. If pregnancy does not occur, the egg is absorbed and the womb lining comes away (menstrual flow).
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Exogenous zeitgebers may synchronise menstrual cycles.
Stern and McClintock (1998) studied 29 women with irregular periods. Pheromones were taken from some at different stages of their cycles, via a cotton pad under their armpits. These pads were cleaned with alcohol and later rubbed on the upper lips of the other participants.
68% of women experienced changes to their cycle which brought them closer to the cycle of their 'odour donor
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SAD is another infradian rhythm.
Seasonal affective disorder (SAD) is a depressive disorder (low mood, lack of activity) with a seasonal pattern.
Often called the winter blues' because the symptoms are triggered during the winter months when the number of daylight hours becomes shorter.
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SAD may be
Caused by
the hormone melatonin.
During the night, the pineal gland secretes melatonin until dawn, where there is an increase in light.
However, during the winter, the lack of light until later in the morning means secretion continues for a bit longer.
This has a knock on effect for the production of serotonin in the brain ( and low serotonin is linked to depressive symptoms)
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ultradian rhythms (more than one cycle in 24 hours) - Stages of sleep are an ultradian rhythm
Sleep pattern occurs in 90-minute periods (i.e. more than one cycle in 24 hours - ultra diem meaning 'beyond' a day).
Divided into five stages, each characterised by a different level of brainwave activity (monitored using EEG).
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Five stages of sleep have been identified.
Stages 1 + 2: Light sleep where a person may be easily woken. In stage 1, brain waves are high frequency and have a short amplitude. In stage 2, the alpha waves continue but occasional sleep spindles
Stages 3 + 4: This is known as deep sleep or slow wave sleep (SWS). The individual waves now have lower frequency and higher amplitude. It is difficult to wake someone at this point.
Stage 5 (REM sleep): The body is paralysed yet brain activity closely resembles that of the awake brain. During this time, the brain produces theta waves and the eyes occasionally move around, thus rapid eye movement (REM)
Dreams most often experienced during REM sleep, but may also occur in deep sleep.
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One strength of infradian rhythms (evolutionary)
- reach on the menstrual cycle shows its evolutionary basis
for our distant ancestors it may have been advantageous for females to menstruate together and become pregnant at the same time
in a social group, it would allow babies who have lost their mothers to have access to breast milk, thereby improving their chances of survival
this suggests that synchronisation is an adaptive strategy
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Limitation of infradian rhythms (confounding variables)
- the Methodology used in synchronisation studies
there are many factors that may change a woman's menstrual cycle and act as confounding variables e.g stress, diet
any supposed pattern may occur by chance. This may be why other studies e.g Trevathan have not replicated stern and McCklintock's original findings
this suggests that menstrual synchrony studies are flawed
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strength of ultradian rhythms (age)
-age related chances in sleep
SWS reduces with age. growth hormone is produced during SWS so this becomes deficient in older people
van Cauter et al suggest the reduced sleep may explain impairments in old age. SWS sleep can be improved using relaxation and medication
this suggests that knowledge of ultradian rhythms has practical value
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limitation of ultradian rhythms (individual differences)
- individual differences in sleep stages
Tucker at al (2097) found large differences between participants in the duration of stages 3 and 4
they suggest that these differences are biologically determined
this makes it difficult to describe 'normal sleep' in any meaningful way
82
Endogenous pacemakers and the sleep/wake cycle - SCN is a primary endogenous pacemaker.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells in the hypothalamus which helps maintain circadian rhythms (e.g. sleep/wake cycle).
Nerve fibres from the eye cross at the optic chiasm on their way to the right and left visual areas. The SCN lies just above the optic chiasm and receives information about light from this structure.
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Influence of SCN on the sleep/ wake cycle demonstrated with chipmunks and hamsters.
DeCoursey et al. (2000) destroyed SC connections in the brains of 30 chipmunks which were returned to their natural habitat and observed for 80 days. Their sleep/wake cycle disappeared and many were killed by predators.
Ralph et al. (1990) bred 'mutant' hamsters with a 20-hour sleep/wake cycle. SC cells were transplanted from the foetal tissue of these hamsters into the brains of normal hamsters, which then developed cycles of 20 hours.
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Pineal gland and melatonin are endogenous mechanisms.
The SC passes information on day length to the pineal gland which increases production of melatonin during the night.
Melatonin is a hormone that induces sleep and is inhibited during periods of wakefulness. It has also been suggested as a causal factor in seasonal affective disorder.
85
Exogenous zeitgebers and the sleep/wake cycle - External environmental factors that reset biological clocks.
The German word zeitgeber means 'time giver
Resetting biological clocks is a process known as entrainment.
Without external cues, the free-running biological clock continues to 'tick' in a cyclical pattern.
Zeitgebers reset the sleep/wake cycle (interaction of internal and external factors).
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Light is a key exogeneous. zeitgeber that influences the sleep/wake cycle.
Light can reset the body's main endogenous pacemaker (SCN). and also has an indirect influence on key processes in the body controlling hormone secretion, blood circulation, etc.
Campbell and Murphy (1998) woke 15 participants at various times and shone a light on the backs of their knees
- producing a deviation in the sleep/wake cycle of up to three hours. Light does not necessarily rely on the eyes to influence the SCN.
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Social cues also have an important
influence on the sleep/wake cycle.
The sleep/wake cycle is fairly random in human newborns, but most babies are entrained by about 16 weeks.
Schedules imposed by parents are a key influence, including adult-determined mealtimes and bedtimes.
Research on jet lag shows adapting to local times for eating and sleeping (not responding to one's own feelings of hunger and fatigue) entrains circadian rhythms and tackles jet lag
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Limitation of SCN research (obscure other clocks)
- it may obscure other body clocks
Body clocks (peripheral oscillators) are found in many organs and cells e.g lungs and skin. They are highly influenced by the actions of SCN but can act independently
Damiola et al 2000 showed how changing feeding patterns in mice altered circadian rhythms of cells in the liver for up to 12 hours, leaving the SCN unaffected
this suggests there may be other complex influences on the sleep/wake cycle, aside from the master clock (SCN)
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Limitation of SCN research (isolation)
- endogenous pacemakers cannot be studied in isolation
only in exceptional circumstances are endogenous pacemakers 'free running' and unaffected by the influence of exogenous zeitgebers
Totak isolation studies are rare. In every day life, pace markers and zeitegers interact so it may make little sense to separate the two
this suggests the more researchers attempt to isolate the influence of internal pacemakers, the lower the validity of the research
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limitation of exogenous zeitgebers (diff environments)
- effects of exogenous zeheh differ in different environments
Exogenous do not have the same effects on people who live in places where there is verify little darkness in the summer and very little light in winter
for instance the innuit Indians or the arctic circle have similar sleep patterns all year round, despite spending around 6 months in almost total darkness
this suggests the sleep/wake cycle is primarily controlled by endogenous pacemakers that can override environmental changes in light
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Another limitation of exogenous zeitgebers (blind man)
-case study evidence undermines effects of exogenous cues
miles et al reported the case of a man, blind from birth, with an abnormal circadian rhythm of 24.9 hours
despite exposure to social cues, such as mealtimes, his sleep/wake cycle could not be adjusted
this suggests that social cues alone are not effective in resetting the biological rhythm and the natural body clock is stronger
