Biopsycholgoy Flashcards
1
Q
What is localisation of function?
A
Theory that different areas of the brain are responsible for different behaviours, processes or activities.
2
Q
Where is the motor area and what is it responsible for?
A
Region of the frontal lobe
Involved in regulating movement
3
Q
Where is the somatosensory area and what is it responsible for?
A
An area of the parietal lobe
Processes sensory information such as touch.
4
Q
Where is the visual area and what is it responsible for?
A
Part of the occipital lobe that receives and processes visual information
5
Q
Where is the auditory area and what is it responsible for?
A
Located in the temporal lobe and concerned with the analysis of speed h- based info.
6
Q
Where is the Broca’s area and what is it responsible for?
A
Area of the frontal lobe of brain in left hemisphere
Responsible for speech prodcution
7
Q
Where is the wernicke’s area and what is it responsible for?
A
Area of the temporal lobe in left hemisphere
Responsible for language comprehension
8
Q
Hemispheres of the brain and the cerebral cortex
A
- Brian divided into 2 symmetrical halves, left and right hemispheres.
- left hemisphere controls right side of body
- right hemisphere controls left side of body
- outer layer of both hemispheres is the cerebral cortex.
- its 3mm thick.
9
Q
What are the 2 hemispheres sub divided into?
A
- 4 lobes
- frontal lobe, parietal lobe, occipital lobe and temperole lobe
10
Q
What happens if motor area is damaged?
A
May result in loss of control over fine movements.
11
Q
What is at the front of both parietal lobes?
A
Somatosensory area
12
Q
What separates the somatosensory area from the motor area?
A
A ‘valley’ called CENTRAL SULCUS
13
Q
The amount of somatosensory area devoted to a particular body part is determined by what?
A
It denotes its sensitivity
E.g face and hands occupy over half of the somatosensory area.
14
Q
If the visual area is damaged what happens?
A
Can produce blindness in part of the right visual field of both eyes.
15
Q
What can damage to the auditory area cause?
A
May produce partial hearing loss
16
Q
What happens if the Broca’s area is damaged?
A
Causes Broca’s aphasia which is characterised by speech slow, labourious and lacking in fluency
17
Q
What happens if the wernicke’s area is damaged?
A
Results in Wernicke’s anpahsia
- produce nonsense words (neologism) as part of the content of their speech.
18
Q
Localisation of function
EVALUATION
Brain scan evidence of localisation
A
- there is a wealth of evidence providing support for the idea that many neurological functions are localised, particularly in relation to language and memory.
- Peterson et al used brain scans to demonstrate how Wernicke’s area was active during the listening task and Broca’s area was active during a reading task, suggesting that these areas of the brain have different functions.
- similarly, a study of long-term by Tulving et al 1994- revealed semantic and episodic memories reside in different parts of the prefrontal cortex.
- brain scans and other scans can be used to test these theories.
19
Q
Localisation of function
EVALUATION
Neurosurgical evidence
A
- The practice of surgically removing or destroying areas of the brain to control aspects of behaviour developed in 1950s.
- early attempts like lobotomy’s were brutal and imprecise and typically involved severing connections in frontal lobe in attempt to control aggressive behaviour.
- controversially, neurosurgery is still used today, like in extreme cases in OCD and depression.
- example: reported 44 OCD patients who had undergo CINGULOTOMY (procedure that involves lesion in of the cingulate gyrus.
- at post surgical follow up after 32 weeks, a 1/3 met the criteria for successful response to surgery.
- 14% for partial response.
- the success of procedures like this strongly suggests that symptoms and behaviours associated with serious mental disorders are localised.
20
Q
Localisation of function
EVALUATION
Case study evidence.
A
Phineas Gage:
- sustained injury when working on railway line.
- explosion hurled meter length pole through Gage’s left cheek and passing behind left eye, and existing his skull from top of his head taking a portion of his brain with it- most of his left frontal lobe.
- he survived but damage to personality.
- was calm and reserved before but after accident he was rude and quick tempered.
- frontal lobe may be responsible for regulating mood.
21
Q
What is plasticity?
A
This describes the brains tendency to change and adapt (functionally and physically) as a result of experience and new learning.
22
Q
What is functional recovery?
A
A form of plasticity.
Following damage through trauma, the brains ability to redistribute or transfer functions usually performed by a damaged area to other, undamaged areas
23
Q
During infancy, the brain experiences a rapid growth in the number of synaptic connects it has- when does this peak (name the psychologists too)?
A
Approximately 15,000 at age 2-3 years old.
(Gopnick et al 1999)
- equates to around 2x as many in adult brain
24
Q
What is synaptic pruning?
A
As we age, rarely used connections are deleted
And frequently used connections are strengthened.
25
Explain Eleanor Maguire et al (2000) research into plasticity:
- studied brains of London taxi drivers and found significantly more volume of grey matter in posterior hippocampus than in matched control group.
- this part of brain associated with development of spatial and navigational skills in humans and other animals.
- as part of Trianon, London cap drivers must complete test called ‘The Knowledge’- this assesses their recall of city streets and possible routes
- appears that this learning experience alters the structure of the taxi drivers brains
- the longer they were in the job, the more pronounced the structural difference was (positive correlation).
26
Explain Draganski et al 2006 research into plasticity
- imaged the brains of medical students 3 months before and after their final exams.
- Leanring- induced changes were seen to have occurred in the posterior hippocampus and parietal cortex, presumably as a result of the exam.
27
Explain functional recovery of the brain after trauma.
- following physical injury, or other forms of trauma, unaffected areas of brain are often able to adapt and compensate for those areas that are damaged.
- this process can occur quickly after trauma (spontaneous recovery) and then slow down after several weeks or months.
- at this point, individual may require rehabilitative therapy to further their recovery
28
What happens in Brian during recovery?
- brain able to rewrite and recognise 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/ ‘unmasked’ to enable functioning to continue.
29
What is axonal sprouting?
The growth of new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways.
30
Plasticity and functional recovery after trauma
EVALUATION
Practical application
- understanding process involved in plasticity has contributed to field of neurorehabiliration
- following illness or injury to brain, spontaneous recovery tends to slow down after number of weeks so forms of psychical therapy may be required to maintain improvements in functioning.
- techniques include movement therapy, electric stimulation of brain to counter the deficits in motor and or cognitive functioning that may be experienced following stoke.
This shows that although brain may have capacity to fix itself to point, this process requires further intervention if it is to be completely successful.
31
Plasticity and functional recovery after trauma
EVALUATION
Negative plasticity
- brains ability to wire self can sometimes have maladaptive behavioural consequences.
- prolonged drug use has been shown to result in poorer cognitive functioning as well as an increased risk of dementia later in life (Madina et al 2007).
- 60-80% of amputees also known to develop PHANTOM LIMB SYNDROME
-thought to be due to cortical reorganisation in the somatosensory cortex that occurs as a result of limb loss.
32
Plasticity and functional recovery after trauma
EVALUATION
Age and plasticity
- function plasticity tends to reduce with age
- brain has a greater propensity for recognition in childhood as it is constantly adapting to new experiences and learning.
- although Bezzola et al 2012- demonstrated how 40hrs of golf training produced changes in the neural representation of movement in participants aged 40-60.
- using fMRI the researches observed reduced motor cortex activity in the novice golfers compared to control group, suggesting more efficient neural representations after training.
- shows that neural plasticity does continue throughout lifespan
33
What is hemispheric lateralisation?
Idea that 2 halves of brain are functionally different and that certain mental processes and behaviours are mainly controlled by 1 hemisphere rather than the other, as in the example of langue (which is localised as well as lateralised).
34
What is split brain research?
Series of studies which began in the 1960s (are still ongoing) involving epileptic patients who had experienced a surgical separation of the hemispheres of the brain.
This allowed researchers to investigate the extent to which brain function is lateralised.
35
What suggests that language is subject to hemispheric lateralisation?
The ability to produce and understand language is controlled by the left hemisphere.
The specialised areas associated with language are found in one of the brains hemispheres rather than both.
36
What was Sperry’s 1968 research on?
- involves unique group of individuals, all of whom had undergone the same surgical procedure: COMMISSUROTOMY- where the corpus callosum and other tissues which connect 2 hemispheres were cut down the middle in order to separate the 2 hemispheres and control frequent and severe epileptic seizures.
This allowed sperry to see the extent to which the 2hemispheres were specialised for certain functions, and whether the hemispheres performed tasks independently of one another.
37
What was the procedure of sperrys research?
- an image or word projected to the patients right visual field (processed by left hemisphere)
- and same or different image could be projected to left visual field (processed by right hemisphere).
- in normal brain, corpus callosum would immediately share the info between both hemispheres giving a complete picture of the visual world.
- however presenting the image to 1 hemisphere of a split brain patient meant that the info could not be conveyed from hemisphere to the other.
38
Describe the key findings of Sperry’s research into split brains.
- describing what you see
- when a picture of an object shown to a patients right visual field, patient could easily decide what was seen.
- if however same object was shown left visal field, patient could not describe what was seen, typically reported that there was nothing there.
- due to left visual field being processed by right hemisphere where there is no language centres.
39
Describe the key findings of Sperry’s research into split brains.
- recognition by touch
- although patients could not attach verbal labels to objects projected in eft visual field, they were able to select a matching object from a grab-bag of different objects using their left land (linked to right hemisphere)
- the objects were placed behind a screen so as not to be seen.
- left hand was also able to select an object that was most closely associated with an object presented to left visual field.
- in each case, the patient was not able to verbally identify what they has seen but could nevertheless ‘understand’ what the object was , using the right hemisphere and select the corresponding object accordingly.
40
Describe the key findings of Sperry’s research into split brains.
- composite words
- if 2 words were presented simultaneously, one on either side of visual field e.g key on left and ring on right.
- patient would write with their left hand the word ‘key’ (left hand goes to right hemisphere linked to left visual field) and say the word ‘ring’
41
Describe the key findings of Sperry’s research into split brains.
- matching faces
- right hemisphere appeared dominant in terms of recognising faces.
- when asked to match a face from a series of other faces, the picture processes by the right hemisphere (left visual field) was consistently selected
- whilst the picture presented to the left hemisphere was consistently ignored.
- when composite picture made up of 2 different halves of a face was presented- 1/2 to each hemisphere, left hemisphere dominated in terms of verbal description whereas the right hemisphere dominated in terms of selecting a matching picture.
42
Split brain research
EVALUATION
Demonstrated lateralised brain functions
- Sperry’s pioneering work into the split-brain phenomenon has produced an impressive and sizeable body of research findings.
-main conclusion appears to be that the left hemisphere is more geared towards analytic and verbal tasks whilst the right is more adept at performing spatial tasks and music.
- right hemisphere can only produce rudimentary words and phrases but contributes emotional and holistic content to language.
-research suggests that the left hemisphere is the ANALYSER whist the right hemisphere is the SYNTHESISER- a key contribution to our understanding of brain processes.
43
Split brain research
EVALUATION
Strengths of the methodology
- experiments involving split brain patients made use of highly specialised and STANDARDISED PROCEDURES.
- sperrys method of presenting visual info to one hemispheric field at a time was ingenious.
- typically particpants would be asked to stare at given point, whist one eye was blindfolded.
- image projected would be flashed up for 1 tenth of a second, meaning the split- Brian patient would not have time to move their eye across the image and so spread the info across both sides of the visual field, and subsequently, both sides of brain.
- allowed Sperry to vary. Aspects of the basic procedure and ensured that only 1 hemisphere was receiving info at a time.
- so he developed a very useful and well- controlled procedure.
44
Split brain research
EVALUATION
Theoretical basis
- Sperry’s work prompted a theoretical and physiological debate about the degree of communication between the 2 hemispheres in everyday functioning and the nature of consciousness.
- Pucetti 1977- have suggested that the 2 hemispheres are so functionally different that they represent a form of DULALITY in the brain- that in effect we have 2 minds (only emphases rather than created in split brain patient.
- in contrast, other researchers have argued that far from working in isolation, the 2 hemispheres form a highly integrated system and are both it involved in most everyday tasks
45
What is an FMRI (Functional magnetic resonance imaging)?
Method used to measure brain activity while a person if performing a task that uses MRI tech (detecting radio waves from changing magnetic fields).
This enables researchers to detect which regions of the brain are rich in oxygen and so are active.
46
What is an EEG? (Electroencephalogram)?
A record of the tiny electrical impulses produced by the brains activity.
- by measuring characteristics wave patterns, the EEG can help diagnose certain conditions of the brain.
E.g epilepsy’s, tumours and dormers of sleep
47
What is ERPs? Event - related potentials
The brains electrophysiological response to specific sensory, cognitive or motor event can be isolated through statistical analysis of EEG data
48
What is post- mortem examinations?
The brain is analysed after death to determine whether certain observed behaviours during the patients lifetime can be linked to abnormalities in the brain.
49
Functional magnetic resonance imaging
EVALUATION
Strengths
- unlike other scanning techniques such as PET, it does not rely on use of radiation
- if administered correctly it is virtually risk free, non invasive and straight forward to use.
- it produces images that have very high spatial resolution, depicting detail by the millimetre, and providing a clear picture of how brain activity is localised.
50
Functional magnetic resonance imaging
EVALUATION
Weaknesses
- fMRI = expensive compared to other neuroimaging techniques
- can only capture a clear image if the person stays perfectly still
- poor temperol resolution because there is around a5 second time-lag behind the image on screen and initial firing of neuronal activity.
- fMRI can only measure blood flow in brain, cannot home in on activity of individual neurons and so it can be difficult to tell exactly what kind of brain activity is being represented on screen
51
Electroencephalogram (EEG)
EVALUATION
Strengths
- EEG proved invaluable in diagnosis of conditions such as epilepsy (random bursts of activity in brain that can be easily detected on screen.
- contributed to our understanding of stages involved in sleep.
- EEG has extremely high temporal resolution
- can accurately detect brain activity at a resolution of a single millisecond.
52
Electroencephalogram (EEG)
EVALUATION
Weakness
- main drawback of EEG lies in the generalised nature of the info received
- EEG signals is no useful for pinpointing the exact source of neural activity, and it does not allow researchers to distinguish between activities originating in different but adjacent locations.
53
Event- related potentials
EVALUATION
Strengths
- bring much more specificity to the measurement of neural processes than could ever be achieved using raw EEG data.
- ERPs are derived from EEG measurements
- have excellent temporal resolution.
54
Event- related potentials
EVALUATION
Weaknesses
- lack of standardisation in ERP methodology between different research studies which makes it difficult to confirm findings.
- in order to establish pure data in ERP studies, background noise and extraneous material must be completely eliminated (this may not always be easy to achieve).
55
Post- mortems
EVALUATION
Strengths
- post mortem evidence= vital in providing a foundation for early understanding of key processes in the brain.
- Broca + Wernicke both relied on post mortems studies in establishing links between language, brain and behaviour decades before neuroimaging ever became a possibility.
- they improve medical knowledge and help generate hypotheses for further study.
56
Post- mortems
EVALUATION
Weaknesses
- Causation is an issue within these investigations
- observed damage to the brain ma not be linked to the deficits under review but to some other unrelated trauma or decay.
- ethical issues of consent from patients before death.
- patients may not be able to provide INFORMED CONSENT e.g in case of HM who lost his ability to form memories and was not able to provide consent- but post-mortem research was conducted on his brain.
57
What is a biological rhythm?
Distinct patterns of changes in body activity that conform to cyclical time periods.
Biological rhythms are influenced by internal body clocks (endogenous pacemakers) as well as external changes to the enviroment (exogenous zeitgebers).
58
What is a circadian rhythm?
Type of biological rhythm, subject to a 24 hr cycle, which regulates a number of body processes such as the sleep/wake cycle and changes in core body temperature.
59
Give an example of an exogenous zeitgebers
Light
60
What time of rhythms occur many times a day?
Ultradian rhythms
61
What type of rhythms take longer than a day to complete?
Infradian rhythms
62
How long do circadian rhythms last?
And give examples
Around 24 hours
EXAMPLES:
- sleep/wake cycle
- core body temp
63
Describe Siffre’s cave study:
Sleep wake cycle
- self- styled caveman
- September 1962- re surfaced after 2 months in the caves of Southern Alps.
- he was deprived from natural light and sound but adequate food and drink.
- when re surfaced, he thought it was mid August.
- Decade later: performed similar feat but this time for 6 months in a Texan cave
- in each case, his ‘free-running’ biological rhythm settled down to on that was beyond the usual 24 hours (around 25 hours) though he did continue to fall asleep and wake up on a regular schedule.
64
Describe Aschoff and Weber 1976
- circadian rhythms
- convinced group of particpants to spend 4 weeks in a WW2 bunker deprived from natural light.
- all but one of the participants (whose sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24-25 hours).
- suggests that the ‘natural’ sleep/wake cycle may be slightly longer than 24 hours but that it is entrained by exogenous zeitgebers associated with our 24 hour day (such as number of daylight hours an typical meal times.).
- however shouldn’t overestimate infleucne of environmental cues on our internal biological clock.
65
Describe Folkard et al 1985study
Cicdain rhythms
- studied group of 12 people who agreed to live in a dark cave for 3 weeks
- went to bed when clock said 11.45pm
- wake up 7.45 am
- over course of study, the researchers gradually speeded up the clock (unknown to participants) so an apparent 24 hour day eventually lasted only 22 hours.
- was revealed that not one of the particants was able to comfortably adjust to new regime.
- this would suggest the existence of a strong free-running circadian rhythm that cannot easily be overridden by changes in the external environment
66
Circadian Rhythm
EVALUATION
Practical application to shift work
- knowledge of circadian rhythms has given researchers better understanding of the adverse consequences that can occur as a result of their disruption.
- e.g night workers engaged in shift work experience a period of reduced concentration around 6 in morning (CIRCADIAN TROUGH) meaning mistakes and accidents are more likely (Bolivian et al 1996).
- Research has also suggested a relationship between shift work and poor health: shift workers are 3 times more likely to develop heart disease (Knutson 2003) which may in part be due to stress of adjusting to different sleep/wake patterns and the lack of poor quality sleep during the day.
- so research into the sleep/wake cycle may have economic implications in terms of how best to manage worker productivity.
67
Circadian Rhythm
EVALUATION
Practical application to drug treatments
- circadian rhythms co-ordinate a number of the body’s basic processes such as heart rate, digestion and hormone levels.
- this in turn has affect on pharmacokinetics (the actions of drugs on body and how well they are absorbed and distributed
- research into circadian rhythms has revealed that there are certain peak times during day or night when drugs are likely to be at their most effective.
- this has lead to the development of guidelines to do with the timing of drug dosing.
68
Circadian Rhythm
EVALUATION
Use of case studies and small samples
- studies of sleep/wake cycle tend to involve small groups of particpants (as in experiment by Ashoff and Wever and also Siffre).
- people involved may not be representative of the wider population and this limits the extent to which meaningful generalisations can be made.
- E.G in Siffres most recent cave experience 1999- observed at the age of 60, that his internal clock ticked much more slowly than when he was a young man.
-illustrates the fact that, even when the same person is involved, there are factors that vary which may prevent neural conclusions being drawn.
69
Circadian Rhythm
EVALUATION
Poor control in studies
- although particpants in the studies were deprived of natural light, they still had access to artificial light.
- for instance, Siffre turned on lamp eveytime he woke up which remained on until he went to bed.
-it was assumed by him and others that artificial light, unlike daylight, would have no effect on the free- running biological rhythm.
- however in tests, Czeisleretal 1999, were able to adjust particpants circadian rhythms form 22 to 28 hours using dim lighting,
- the use of light may be analogous to particpants taking a drug that resents their bio clock.
70
Define infradian rhythm
Type of biological rhythm with a frequency of less than 1 cycle in 24 hours, such as menstruation and seasonal affective disorder
71
Define Ultradian rhythm
Type of biological rhythm with a frequency of more than one cycle in 24 hours, such as stage of sleep.
72
Describe the menstrual cycle in terms of infradian rhythms
- female menstrual cycle governed by monthly changes in hormone levels which regulate ovulation.
- cycle refers to the time between the first day of woman period (when the womb longing is shed) to the day before her next period.
-typical cycle takes approx 28 days
- during each cycle, rising levels of the hormone oestrogen cause the ovary to develop egg and release (ovulation).
- after ovulation, hormone progesterone helps the womb lining to grow thicker, readying the body for pregnancy.
- if pregnancy does not occur, egg absorbed by body, womb lining comes away and leaves body (menstrual flow)
73
Describe the study into menstrual cycles
- Stern + McClintock 1998
- involved 29 women with a history of irregular periods.
- samples of pheromones were gathered from 9 of the women at different stages of their menstrual cycles, via cotton pad placed in their armpit.
- pads were treated with alcohol and frozen
- the rubbed n upper lip of other participants.
- on day 1, pads from the start of menstrual cycle were applied to all 20 women, on day 2 they were all given pad from second day of cycle and so on.
FOUND:
- 68% of women experienced changes to their cycle which bought them closer to the cycle to their ‘odour donor’.
74
Describe SAD- seasonal affective disorder
- depressive disorder which has seasonal pattern of onset
- low mood, lack of interest in life
- triggered in winter months when number of daylight hours becomes shorter.
- classed as circadian rhythm as the experience of SAD may be due to the disruption of the sleep/wake cycle and this can be attributed to prolonged periods of daily darkness during winter.
- Psychologists have hypothesised that the hormone MELATONIN is implicated in the cause of SAD.
- during night pineal gland secretes melatonin until dawn when there is an increase in light.
- during winter lack of light in morning means this secretion process continues longer.
- this is thought t have a knock-on effect not he production of serotonin on brain- chemical that has been linked to onset of depressive symptoms.
75
How can sleep cycle be monitored
Using an EEG
76
Describe Stage 1 and 2 of the sleep cycle (Ultradian rhythm)
- light sleep where the person can be woken easily.
- at beginning of sleeep, brainwave patterns start to become slower and more rhythmic (alpha waves), becoming even slower as sleep becomes deeper (theta waves).
77
Describe Stage3 and 4 of the sleep cycle (Ultradian rhythm)
Involves delta waves which are slower still and have a greater amplitude than earlier wave patterns.
This is deep sleep or slow wave sleep and it is difficult to rouse someone at this point.
78
Describe Stage 5 and REM sleep of the sleep cycle (Ultradian rhythm)
- body is paralysed yet brain activity speeds up significantly in a manner that resembles the awake brain.
- REM stands for rapid eye movement to denote the fast, jerky activity of the eyes under the eyelids at this point.
- research has suggested that REM activity during sleep is highly correlated with he experience of dreaming.
79
Infaradian and Ultradian rhythms
EVALUATION
Evolutionary basis of the menstrual cycle
- menstrual synchrony (kind observed in McClintock study) is thought by many to have an evolutionary value.
- ancestors: may have been advantageous for females to menstruate together and therefore fall pregnant around the same time.
- would mean that new-born could be cared for collectively within a social group increasing the chances of the offspring’s survival.
- validity of the evolutionary perspective has been questioned by some.
- Schank 2004- has argued that if there were too many females cycling together within a social group, this would produce competition for the highest quality males (thereby lowering the fitness of any potential offspring).
80
Infaradian and Ultradian rhythms
EVALUATION
Methodological limitations in synchronisation studies
- criticisms have been made of salty synchronisation studies and the methods employed.
- there could be many factors that may effect change in a women’s menstrual cycle, including stress, changes in diet, exercise ect, that night act as confounding variables.
- means that any supposed pattern of synchronisation, as seen in the studies by McClintock and other, is no Moore than would have been expected to occur by chance.
- in addition, research typically involves small samples of women and relies on particpants self-reporting the onset of their own cycle.
81
Infaradian and Ultradian rhythms
EVALUATION
Evidence supports the idea of distinct stages in sleep
- landmark study by Dement + Kleitman 1957- monitored the sleep patterns of 9 adult participants in sleep lab.
- brainwave activity was recorded on the EEG and the researchers controlled for the effects of caffeine and alcohol.
- REM activity during sleep was highly correlated with he experience of dreaming, Brian activity varied according to how vivid dreams were, and participants woken during dreaming, reported very accurate recall of. Their dreams.
- replications of this investigation have noted similar findings, though the small size of the original sample has been criticised by some.
82
What are endogenous pacemakers?
Internal body clocks that regulate many of our biological rhythms, such as the infleucne of the suprachiasmatic nucleus (SCN) on the sleep/wake cycle.
83
What are exogenous zeitgebers?
External cues that may affect or entrain out biological rhythms, such as the influence of light on sleep/wake cycle.
84
What is the sleep/wake cycle?
A daily cycle of biological activity based on a 24 hour period (circadian rhythm) that is influenced by regular variations in the enviroment, such as the alternation of night and day.
85
Explain the suprachiasmaic nucleus (SCN)
- its a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
- one of the primary endogenous pacemakers in mammalian species.
- its influential in maintaining circadian rhythms such as sleep/wake cycle.
- nerve fibres connected to the eye cross in an area called the OPTIC CHIASM on their way to the visual area of the cerebral cortex.
- the SCN lies just above the optic chiasm.
- it receives info about light directly from this structure.
- continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
86
Animal studies and the SCN
- influence of the SCN has been demonstrated in studies involving animals.
- DeCoursey et al 2000, destroyed the SCN connections in the brain of 30 chipmunks who were then returned to their natural habitat and observed for 80 days
- the sleep/wake cycle of the chipmunks disappeared and by end of study a significant proportion of them had been killed by predators (presumably because they were awake and vulnerable to attack when they should have been asleep).
- in another study’s Ralph et al 1990 bred ‘mutant’ hamsters with a 20 hour sleep/wake cycle.
- when SCN cells from the foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters, the cycles of the second group defaulted to 20 hours.
- both of these studies emphasise the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
87
Describe the pineal gland and melatonin interns of endogenous pacemakers.
- SCN passes the info on day length and light that it receives to the pineal gland (pea-like structure in the brain just behind the hypothalamus).
- during night, pineal gland increases production of melatonin.
- melatonin has also been suggested as a casual factor in seasonal affective disorder
88
Explain light in terms of the exogenous zeitgebers
- light = key zeitgeber in humans.
- it can reset the body’s main endogenous pacemaker, the SCN, and so plays a role in the maintenance of the sleep/wake cycle.
- light also has an indirect infleucne on key processes in the body that control such functions as HORMONE secretion and blood circulation.
89
Explain a study researching light as an exogenous zeitgebers
Campbell + Murphy 1998
- demonstrated that light may be detected by skin receptor sites on the body even when the same info is not received by the eyes.
- 15 particpants were woken at various times and a light pad was shone on the back of their knees.
- the researchers managed to produce a deviation in the participants usual sleep/wake cycle of up to 3 hours in some cases.
- suggests that light is a powerful exogenous zeitgeber that need not necessarily rely on the eyes onto exert its influence on the brain.
90
Explain a study researching social cues as an exogenous zeitgebers
- infants are seldom on the same sleep/wake cycle as the rest of the family.
- human infants, initial sleep/wake cycle is pretty much random.
- at about 6 weeks of age, the circadian rhythms begin and by about 16 weeks, most babies are entrained.
- the schedules imposed by patients are likely to be key influence here, including adult determined mealtimes and bedtimes.
91
Endogenous pacemakers and exogenous zeitgebers
EVALUATION
Beyond the master clock
- research has revealed there are numerous circadian rhythms in many organs and cells of the body.
- these are called peripheral oscillators, and are found in the adrenal gland, oesophagus, lungs, liver, pancreas, spleen, thymus and skin.
- although these peripheral clocks are highly infleucne by the actins of the SCN, they can act independently.
- Damiola et al 2000- demonstrated how changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours, whilst leaving the rhythm of the SCN unaffected.
- this suggested that there may be many other complex influences on the sleep/wake cycle, aside from the master clock.
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Ethics in animal studies
- problems involved in generalising findings of the sleep/wake cycle from animal studies to humans.
- more disturbing issue, particularly in relation to DeCoursey et al study, is the ethics involved in such research.
- the animals were exposed ti considerable harm, and subsequent risk, when they were returned to their natural habitat.
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Infleucne of exogenous zeitgebers may be overstated
- miles et al 1977 recount the story of a young man, blind from birth, with a circadian rhythm of 24.9 hours.
- despite expose it social cues, his sleep/wake cycle could not be adjusted, and consequently he has to take sedatives at night and stimulants in the morning to keep pace with the 24 hours world.
- similarly, studies of individuals who live in artic regions (sun does not set during summer months)show normal sleep patterns despite the prolonged exposure to light.
- both these examples suggest that there are occasions when exogenous zeitgebers may have little bearing on out internal rhythm.
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Methodological issues in studies
- findings from the Campbell and Murphy study have yet to be replicated.
- other psychologists have been critical of the manner in whihc the study was conducted and have suggested that there may have been some limited light exposure to the participants eyes - a major confounding variable.
- also, isolation one exogenous zeitgeber (light) in this way does not give us insight into the many other zeitgebers that infleucne the sleep/wake cycle, and the extent to which these may interact.
