Biopsychology AO3

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  • Created on: 28-05-22 10:47

Localisation of function and hemispheric lateralis

Peterson (1998) used brain scans to show that Wernicke's area was active in a listening taks, and that Broca's area was active in a reading task, demonstrating that these functions are localised

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Localisation of function and hemispheric lateralis

Rougherty (2002) shows lateralisation of brain function in that neurosurgery can treat OCD by cutting the cingulate gyrus

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Localisation of function and hemispheric lateralis

The equipotentially theory argues that although basic functions such as the motor cortex and sensory functions are controlled by localised brain areas, higher cognitive functions (such as decision-making) are not localised. Research has found that damage to the brain can result in other areas of the brain taking over control of functions that were previously controlled by the damaged area. Therefore, the severity of brain damage is determined by the amount of damage to the brain rather than the particular area that has damaged.

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Localisation of function and hemispheric lateralis

The way in which brain areas are connected with each other may be as important for normal cognitive function as particular brain sites themselves. Brain sites are independent and damage to connections between sites may lead to the brain site not being able to function normally. For example, Dejerine (1982) found that damage to the connection between the visual cortex and Wernicke's area led to an inability to read (vision and comprehension)

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Localisation of function and hemispheric lateralis

Gender differences have been found with females possessing larger Broca's and Wernicke's areas than males

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Split brain research

As a result of split brain patients being so rare, the findings were often based on small samples, and these patients often had other neurological problems which may have acted as a confounding variable. To add to this, patients did not always have a complete splitting of the two hemispheres. These factors mean findings should be generalised with care

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Split brain research

It is assumed that the main advantage of brain lateralisation is that it increases neural processing capacity which is the ability to perform two tasks simultaneously. Rogers et al (2004) found that in a domestic chicken, brain lateralisation is associated with the enhanced ability to perform tasks simultaneously, such as finding food and being vigilant for predators. Using only one hemisphere to engage in a task leaves the other hemispshere free to engage in other functions. This provides evidence for the advantages of brain lateralisation and demonstrates how it can enhance brain efficiency in cognitive tasks

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Split brain research

However, because Roger's research was carried out on animals, it is difficult to conclude the same of humans. Unfortunately, the split brain procedure is rarely carried out now so findings are difficult to generalise to modern society. Such studies often include few participants, and research takes an idiographic approach. Therefore,  any conclusions drawn are representative only of those individuals who had a confounding disorder that made the procedure necessary. This is problematic as such results cannot be extrapolated to the wider population

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Split brain research

Furthermore, research has suggested that lateralisation changes with age. Szaflarski et al (2006) found that language became more lateralised to the left hemisphere with increasing age in children and adolescents, but after the age of 25 lateralisation decreased with each decade of life. This raises the question about lateralisation, such as whether eveyone has one hemisphere that is dominant over the other and whether this dominance changes with age

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Split brain research

It may be argued that language may not be restricted to the left hemisphere. Turk et al (2002) studied JW who suffered damage to the left hemisphere but developed the capacity to speak in the right hemisphere, eventually leading to the ability to speak about the information presented to either side of the brain. This suggests that perhaps lateralisation is not fixed and that the brain can adapt following damage to certain areas. This limits the application of research findings as individual differences may play a role

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Split brain research

Research is done using highly controlled and standardised procedures. For example, Sperry investigated one hemispheric field by restricting visual information to one field at a time. An image would be flashed for 1/10th of a second, so participants would not have time to move the eye across the image and spread the information to both sides of the visual field. Therefore, this developed a well-controlled procedure that could be replicated easily

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Maguire (2002) showed that London taxi drivers had more grey matter in the posterior hippocampus compared to control subjects. This area of the brain is linked to spatial awareness and navigation skills. The amount of change was postively correlated with how long they had been a London taxi driver for

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Learning and new experiences cause new neural pathways to strengthen whereas neural pathways which are used infrequenctly become weak and eventually die. Thus brains adapt to changed environments and experiences. Boyke (2008) found that even at 60+ years old, the learning of a new skill resulted in an increased neural growth in the brain area associated with the skill

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Kempermann (1998) found that rats housed in more complex environments showed an increase in neurons compared to a control group living in simple cages. Changes were particularly clear in the hippocampus which is associated with memory and spatial navigation

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Functional recovery

Teuber (1975) found that 60% of soldiers aged under 20 showed signs of improvement after trauma, compared to only 20% of those aged over 26

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Functional recovery

Danielli (2003) studied a 2.5 year old boy who had his left hemispehere removed. After rehabilitation, at the age of 17 he had only minor language problems due to the the fact that the right hemisphere had compensated for the damage

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Functional recovery

Elbert et al concluded that the capacity for neural reorganisation is much greater in children than in adults, meaning that neural regeneration is less effective in older brains. This may explain why adults find change more demanding than young people. Therefore, indivdiual differences must be considered when assessing the likelihood of functional recovery in the brain after trauma

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Functional recovery

A strenght of research examining plasticity and functional recovery is the application of the findings to the field of neurorehabilitation. Understanding the processes of plasticity and functional recovery led to the development of this field, which uses motor therapy and electrical stimulations of the brain to counter the negative effects and deficits in motor and cognitive functions following injuries. This demonstrates the postive application of research in this area to help improve the cognitive functions of people suffering from injuries

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fMRI's strengths

Creates moving picture of brain acitivity allowing you to see how processes take place

It is a non-invasive technique and does not expose the brain to potentially harmful radiation

Creates a high resolution image of the brain (1mm)

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fMRI's limitations

Only measures blood flow - it does not directly measure neural acitivity so is not a completely objective measure of neural activity in the brain

May overlook the interconnectivity of brain sites. By only focussing on brain sites receiving increased blood flow, it fails to account for the importance of brain sites communicating with each other

Very expensive and machines are difficult to build/transport

It can take up to 5 seconds to create an image after the brain acitivity has occurred

Consciousness and personality have not been found to be localised to any one part of the brain. This is backed up by Lashley (1950) who found that processes involved in higher functions are not localised. Lashley removed 10-50% of the cortex of a rat's brain and found no one area was more important for learning to navigate a maze

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EEG's strengths

Records brain activity over time and can therefore monitor changes as a person switches from task to task or one state to another (e.g. sleeping)

They have medical applications in diagnosing disorders such as epilepsy and Alzheimer's

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EEG's limitations

Only monitor electrical activity in the outer layers of the brain and therefore cannot reveal electrical activity in deeper brain sites

Not highly accurate, therefore cannot distinguish in activity between two closely adjacent brain areas

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ERP's strengths

Provide a continuous measure of neural activity in response to a stimulus. Therefore, changes to the stimulus can be directly recorded. For example, if a blue coloured slide turned green

It only takes milliseconds to take a reading, compared to several seconds for the fMRI

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ERP's limitations

Only monitor electrical activity in the outer layers of the brain and therefore cannot reveal electrical activity in deeper brain sites

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Postmortems strengths

They allow for detailed examinations and measurement of deep brain structures, not measurable by brain scans. For example, the hypothalamus

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Postmortems limitations

Various factors can act as confounding variables and may influence findings and conclusions. For example, the length of time between death and the postmortem being carried out, other damage caused to the brain either during death or as a result of disease, age at death, drugs given in months prior to death etc

Modern techniques such as fMRI and EEG have largely replaced postmortems

Brain activity cannot be measured as the person is deceased, so only the damage can be viewed and not how it affected the functioning

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