brain

• Localisation of function is the theory that different areas of the brain are responsible for different behaviours, processes or activities.
• Motor Centres

  • Found at the back of the frontal lobe in both hemispheres is the motor area which controls voluntary movement in the opposite side of the body. Damage to this area can lead to impaired fine movements
• Somatosensory centres

  • Found at the front of both parietal lobes, separated from motor centres by a ‘valley’. This is where sensory information from the skin (e.g. heat, touch) is represented. The amount of somatosensory area devoted to a body part indicates its sensitivity (e.g. over half is given to receptors for face and hands)
• Visual centres (visual cortex)

  • Found 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 vice-versa. Damage to the left hemisphere can, for example, can produce blindness in part of the right visual field of both eyes.
• Auditory centres

  • Located in the temporal lobes. Analyses speech-based information. Damage may produce partial hearing loss or, if Wernicke’s area is damaged it may affect the ability to comprehend language)
• Language centres

  • Language is restricted to the left side of the brain in most people
• Broca’s area

  • Small area in the left frontal lobe responsible for speech production. Damage to this area can lead to Broca’s aphasia which is characterised by speech that is slow and lacking in fluency.
• Wernicke’s area

  • Area in the left temple lobe responsible for language comprehension. Damage can lead to Wernicke’s aphasia where patients produce nonsense words as part of the content of their speech.
• There is research evidence to support the localisation of function in the brain. For example, Petersen (1988) used brain imaging to show that Wernicke’s area was active during a listening task and Broca’s area

  was active during a reading task. Furthermore, Tulving et al (1994) revealed that semantic and episodic memories reside in different parts of the prefrontal cortex. This supports localisation of function in the brain, with brain imaging studies providing objective methods for

  studying which parts of the brain show increased activity when tasks are undertaken.
• Furthermore, neurosurgery which involves removing or destroying part of the brain, offers further evidence for localisation of function. In a study of 44 patients with OCD who had undergone a cingulotomy, it was found that a third met the criteria for successful response to the surgery after 32 weeks. The success of such treatments therefore supports the proposal that symptoms and behaviours associated with disorders such as OCD are localised to specific areas of the brain.
• However, localisation of function is challenged by the concept of plasticity. When the brain becomes damaged and a particular function is impaired or lost, the rest of the brain appears able to reorganise itself to recover the lost function. For example, there are a number of

  documented cases of stroke patients being able to recover those abilities that were thought to be lost as a result of the illness. The concept of plasticity therefore challenges localisation of function as it appears that such proposals are too simplistic and that a more holistic view of brain functioning is required.
• Hemispheric lateralisation refers to the understanding that one side of the brain controls the opposite side of the body and that each hemisphere is responsible for different functions (e.g. the left is mainly

  concerned with speech and language whereas the right is linked to visual-motor tasks).
• The brain is contralateral - left hemisphere is responsible for the right side of your body and the right hemisphere is responsible for the left side of your body
• Frontal - decision making and reasoning

  Temporal - memory and auditory processing

  Parietal - sensory processing and spatial navigation

  occipital - vision 

  Outside layer of the brain is called the cerebral cortex or the cerebrum
• Case study of Victor Leborgne/’Tan’

  Suffered with epilepsy 

  Lost ability to speak and was hospitalised at 30

  Treated by paul broca

  Conducted a post mortem on his brain - lesion on left frontal lobe 

  Broca decided it was responsible for his production of speech since this was the only place w damage
• Hemispheric lateralisation 

  Not only are certain specific parts of the brain responsible for key behaviours, but also each hemisphere has its own set of responsibilities

  Hemispheric lateralisation - when a function seems to be carried out by only one hemisphere
• Discuss research into plasticity and functional recovery of the brain after trauma. Refer to the views of the teacher and Xavier in your answer.

  brain plasticity is the ability of the brain to modify the structure and function based on experience

  functional recovery is where the brain recovers abilities previously lost due to brain injury

  neuronal unmasking – activation of ‘dormant’ synapses to compensate for damaged areas of the brain

  evidence from case studies; eg E.B. Danelli et al. (2013) • evidence from animal studies; eg Hubel & Wiesel (1963)
• hemispheric lateralisation refers to the notion that certain functions are principally governed by one side of the brain
• One such case study is that of Phineas Gage, who in 1848 while working on a rail line, experienced a drastic accident in which a piece of iron went through his skull. Although Gage survived this ordeal, he did experience a change in personality, such as loss of inhibition and anger. This change provided evidence to support the theory of localisation of brain function, as it was believed that the area the iron stake damaged was responsible for personality.
• The claim that functions are localised to certain areas of the brain has been criticised. Lashley proposed the equipotentiality theory, which suggests that the basic motor and sensory functions are localised, but that higher mental functions are not. He claimed that intact areas of the cortex could take over responsibility for specific cognitive functions following brain injury. This therefore casts doubt on theories about the localisation of functions, suggesting that functions are not localised to just one region, as other regions can take over specific functions following brain injury.
• Also, critics argue that theories of localisation are biologically reductionist in nature and try to reduce very complex human behaviours and cognitive processes to one specific brain region. Such critics suggest that a more thorough understanding of the brain is required to truly understand complex cognitive processes like language.
• Some psychologists argue that the idea of localisation fails to take into account individual differences. Herasty (1997) found that women have proportionally larger Broca’s and Wernicke’s areas than men, which can perhaps explain the greater ease of language use amongst women. This, however, suggests a level of beta bias in the theory: the differences between men and woman are ignored, and variations in the pattern of activation and the size of areas observed during various language activities are not considered.
• Tulving demonstrated, using PET scans, that semantic memories were recalled from the left prefrontal cortex + episodic memories were recalled from the right prefrontal cortex. This shows how different areas of the brain are responsible for different functions, as predicted by localisation theory. This idea was further supported by Petersen (1988), who found that Wernicke’s area activation is required for listening tasks, whereas Broca’s area is required for reading tasks. This confirms that Wernicke’s area is involved in speech comprehension + Broca's area is responsible for speech production.
• Phineas Gage was injured by a blasting rod which intersected the left side of his face, tearing through his prefrontal cortex. The damage involved both left + right in a pattern that causes a defect in rational decision making and the processing of emotion. Such case studies, particularly those showing marked differences after trauma, demonstrate the idea that some areas of the brain are responsible for specific functions. However, with the use of case studies, the subjectivity of the conclusions drawn and the unusual sample, alongside a lack of control over confounding + extraneous variables
• Plasticity – the brains ability to functionally and physically adapt in response to trauma, new experiences and learning. This is based on the idea of equipotentiality (Lashley, 1930), who argues that individual brain ideas do have simple functions, but it is rather the connection between multiple brain areas that allows for higher level functioning. 
• Functional recovery is the ability of the brain to transfer the functions of areas damaged through trauma, to other healthy parts of the brain, thus allowing for normal functioning to carry on.

  Enabled through equipotentiality, axonal sprouting (formation of new synapses), reformation of blood vessels and recruiting homologous areas of the brain on the opposite side.
• Maguire et al

  London taxi drivers, found that they had a greater amount of grey matter in their mid-posterior hippocampi than in their anterior hippocampi, which is linked to greater awareness of navigation and location knowledge. Also found that the more time the taxi drivers had worked, the greater the grey matter volume in the mid-posterior hippocampi, suggesting a positive correlation. This provides evidence for the brain’s plasticity in its ability to adapt to learning and new experiences
• Sperry (1968) investigated hemispheric lateralisation with the use of split-brain patients. A number of different procedures were employed to test the abilities of split-brain patients. For example, in the ‘describe what you see’ task a picture was presented to either the left or right visual field and the patient had to describe what they saw. It was found that when the picture was presented to the right visual field (processed by the left hemisphere) the patient could describe what they saw, but when the picture was presented to the left visual field (processed by right hemisphere) they could not describe what was shown and often reported that there was nothing present. The inability of the patients to describe objects in their left visual field (processed in the right hemisphere) therefore supports the proposal that language centres are located in the left hemisphere.
• A strength of the experiments using split-brain patients is that they used highly scientific and standardised procedures. For example, the image projected would only be flashed up for one-tenth of a

  second to ensure that the split-brain patient would not have time to move their eye across the image and spread the information across both sides of the visual field (and therefore both sides of the brain). Such controls ensured that only one hemisphere was receiving information at a time, increasing the validity of the approach as a measure of hemispheric lateralisation.
• However, a limitation of the research is that split-brain patients represent an unusual sample of people. Only 11 patients took part in all of the variations of the basic procedure, all of whom had a history of

  epileptic seizures. It has been argued that this may have caused unique changes in the brain that may have influenced the findings. Furthermore, some patients has experienced more disconnection of the two hemispheres than others. Such issues therefore limit the extent to which the findings can be generalised, as they may only represent hemispheric lateralisation in this particular group of patients.
• Furthermore, it could be argued that such research over-simplifies brain function. While distinctions between the functions of the two hemispheres are often made, modern neuroscientists would argue that the actual distinction is much less clear-cut than research such as Perry’s indicates. In a normal brain the two hemispheres are in constant communication when performing everyday tasks, and many behaviours associated with one hemisphere can be carried out effectively by the other when the situation requires it. This is therefore a limitation of split-brain research as it may not reflect the complexity of everyday, normal brain functioning.