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Biopsychology (Localisation of Function (Centres (Somatosensory Area
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Biopsychology
Localisation of Function
Refers to the idea that the certain parts of the brain have different functions. If damaged, the functions performed by the specific area will be affected.
Hemispheres and Cerebral Cortex
- Lateralisation - Certain functions are dominated by a specific hemisphere.
- The left hemisphere controls the right side of the body and the right hemisphere controls the left side of the body.
- The outer layer of the hemispheres is called the cerebral cortex which appears grey due to the location of cell bodies.
Centres
Somatosensory Area
Where sensory information from the skin is represented. Found in both parietal lobes.
Language Area
- Language restricted to the left hemisphere.
- Broca's Area - Left frontal lobe is responsible for speech production. Patient 'Tan' damaged this area and was only able to say 'tan'.
- Wernicke's Area - Left temporal lobe is responsible for speech comprehension. Patients that damaged this area could talk fluently but could not understand speech.
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Visual Area
The right visual field sends information to the left visual cortex and the left visual field sends information to the right visual cortex. Found in the occipital lobe.
Evaluation
Weaknesses
- Lashley (1950) suggests learning is too complex to be localised - Removal of parts of the cortex in rats proved no area to be more important than another while learning a maze.
Strengths
- Petersen et al (1988) - Brain scans showed that Wernicke's area was active during listening tasks and Broca's area was active during reading tasks.
- Dougherty et al (2002) - A third of the 44 OCD patients that had undergone a cingulotomy (a neurosurgical procedure involving lesioning the cingulate gyrus) responded successfully to the surgery. This suggests mental disorders may be localised.
Methods of Investigation
fMRI
Functional Magnetic Resonance Imaging
- When the brain area is more active, it consumes more oxygen so the blood flow is directed to that part (haemodynamic response).
- fMRI detects the changes in oxygenation and flow in parts of the brain and creates 3D images showing which parts of the brain are involved in specific mental processes.
Weaknesses
- Expensive and only produces a good image if the patient is still.
- Poor temporal resolution as there is a 5 second time lag between the image and the initial neuronal activity.
- Difficult to tell what brain activity is occurring as it only measures the blood flow.
Strengths
- Supports localisation of function.
- Does not use radiation, virtually risk-free and non-invasive.
- Images have high spatial resolution so provide a clear picture of the brain.
Post-Mortoms
Analysis of a brain after death - generally done on a person that had a rare disorder or unusual deficits in mental processes. Used to establish the cause of the person's suffering and may involve a comparison with a neurotypical brain.
Strengths
- Improved medical knowledge before neuroimaging was possible.
- Broca and Wernicke relied on post-mortoms.
Weaknesses
- Observed damage to the brain may not be caused by the deficits under review.
- Patients may not be able to provide informed consent before death - patient HM was unable to form memories so could not consent but a post-mortom was still done.
EEG
Electroencephalogram
- Measures electrical activity through electrodes on the patient's scalp.
- Scan recording represents brainwave patterns.
- Unusual arrhythmic patterns may indicate neurological abnormalities.
Strengths
- Used for the diagnosis of conditions like epilepsy.
- Helps us understand the stages of sleep.
- Extremely high temporal resolution - down to a millisecond or less.
Weaknesses
- Cannot pinpoint exact source of neural activity.
ERP
Event-Related Potentials
- An ERP is a type of brainwave triggered by specific events.
- Uses statistical averaging techniques to filter out extraneous brain activity from EEG recordings.
- This presents responses to specific stimuli or the performance of a specific task.
Weaknesses
- Lack of standardisation in ERP methodology makes it difficult to confirm findings.
- To establish pure data, extraneous material must be eliminated which is difficult to do.
Strengths
- Specific measurements of mental processes.
- Excellent temporal resolution so used often when measuring cognitive functions and deficits.
- Researchers have identified different types of ERPs and their functions.
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