Localisation and Lateralisation

• define localisation of function

  Localisation of function is the idea that certain functions (e.g. language, memory, etc.) have certain locations within the brain.
• define hemispheric lateralisation

  Lateralisation is the fact that the two halves of the brain are functionally different and that each hemisphere has functional specialisations, e.g. the left is dominant for language, and the right excels at visual motor tasks.
• define motor area

  The motor area is responsible for voluntary movements by sending signals to the muscles in the body.
• define somatosensory area

  The somatosensory area receives incoming sensory information from the skin to produce sensations related to pressure, pain, temperature, etc.
• define visual area

  The visual area receives and processes visual information. The visual area contains different parts that process different types of information including colour, shape or movement.
• define auditory area


  The auditory area is responsible for analysing and processing acoustic information.
• define broca's area 


  The Broca’s area is found in the left frontal lobe and is thought to be involved in language production.
• define wernicke's area

  The Wernicke’s area is found in the left temporal lobe and is thought to be involved in language processing/comprehension.
• define split-brain research


  Split-brain patients are individuals who have undergone a surgical procedure where the corpus callosum, which connects the two hemispheres, is cut.
• define plasticity

  Brain plasticity refers to the brain’s ability to change and adapt because of experience.
• define functional recovery

  Functional recovery is the transfer of functions from a damaged area of the brain after trauma to other undamaged areas.
• where is the motor area located?

  frontal lobe
• where is the somatosensory area located?

  parietal lobe
• where is the visual area?

  occipital lobe
• where is the auditory area?

  temporal lobe
• describe research into broca's area

  • Tan could understand spoken language but was unable to produce any coherent words, and could only say 'tan'
  • after Tan's death, Broca conducted a post-mortem examination on Tan's brain and discovered that he had a lesion in the left frontal lobe
  • broca concluded that this area was responsible for speech production
  • people with damage to this area experience broca's aphasia
• describe research into wernicke's area

  • found patients with lesions to wernicke's area were still able to speak, but were unable to comprehend language
  • wernicke's area is found in the left temporal lobe and is thought to be involved in language processing/comprehension
  • people with damage to this area struggle to comprehend language, often producing sentences that are fluent, but meaningless
• strength of localisation of function

  • There is a wealth of case studies on patients with damage to Broca’s and Wernicke’s areas that have demonstrated their functions. For example, Broca’s aphasia is an impaired ability to produce language; in most cases, this is caused by brain damage in Broca’s area. Wernicke’s aphasia is an impairment of language perception, demonstrating the important role played by this brain region in the comprehension of language.
• limitations of localisation of function (1)

  • 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 casts doubt on localisation of functions, suggesting that functions are not localised , as other regions can take over specific functions following brain injury.
• limitations of localisation of function (2)

  • 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.
• limitations of localisation of function (3)

  • Finally, 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.
• method of Sperry and Gazzangia (1967)

  • An image/word is projected to the patient’s left visual field (which is processed by the right hemisphere) or the right visual field (which is processed by the left hemisphere).
  • When information is presented to one hemisphere in a split-brain patient, the information is not transferred to the other hemisphere (as the corpus callosum is cut).
• findings of Sperry and Gazzangia (1967)

  Describe what you see:

  
• findings of sperry and gazzangia (1967)

  • tactile test:

  
• findings of sperry and gazzangia (1967)


  drawing tasks:

  
• strength of split-brain research

  • Rogers et al. (2004) found that in a domestic chicken, brain lateralisation is associated with an enhanced ability to perform two tasks simultaneously (finding food and being vigilant for predators). Using only one hemisphere to engage in a task leaves the other hemisphere 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.
• limitations of split-brain research (1)

  • research was carried out on animals, it isdifficult to generalise. Unfortunately, much of the research into lateralisation is flawed because the split-brain procedure is rarely carried out now, meaning patients are difficult to come by. Such studies often include very few participants, and often the research takes an idiographic approach. Therefore, any conclusions drawn are representative only of those individuals. This is problematic as such results cannot be generalised to the wider population.
• what has research demonstrated about plasticity?

  • brain continues to create new neural pathways and alter existing ones in response to changing experiences
• what is neuronal unmasking in functional recovery?

  • where dormant synapses (which have not received enough input to be active) open connections to compensate for a nearby damage area of the brain.
  • this allows new connections in the brain to be activated, thus recovering any damage occurring in specific regions
• strength of plasticity and functional recovery (1)

  • There is further research to support the notion of brain plasticity. Maguire et al. found that the posterior hippocampal volume of London taxi drivers’ brains was positively correlated with their time as a taxi driver and that there were significant differences between the taxi drivers’ brains and those of controls. This shows that the brain can permanently change in response to frequent exposure to a particular task.
• strengths of plasticity and functional recovery (2)

  • There is research to support the claim for functional recovery. Taijiri et al. (2013) found that stem cells provided to rats after brain trauma showed a clear development of neuron-like cells in the area of injury. This demonstrates the ability of the brain to create new connections using neurons manufactured by stem cells.
• limitations of plasticity and functional recovery (1)

  • some psychologists suggest that research investigating the plasticity of the brain is limited. For example, Maguire’s research is biologically reductionist and only examines a single biological factor in relation to spatial memory. This approach is limited and fails to take into account all of the different biological/cognitive processes involved in spatial navigation which may limit our understanding. Other psychologists suggest that a holistic approach to understanding complex human behaviour may be more appropriate.
• strengths of plasticity and functional recovery (3)

  • application of the findings to the field of neurorehabilitation. Understanding the processes of plasticity and functional recovery led to the development of neurorehabilitation which uses motor therapy and electrical stimulation of the brain to counter the negative effects and deficits in motor and cognitive functions following accidents, injuries and/or strokes. This demonstrates the positive application of research in this area to help improve the cognitive functions of people suffering from injuries.