Localisation of function

• What is localisation of function?

  Localisation of function is the different parts of the brain responsible for different functions or activities.
• What is the cortex?

  The cortex is the outer layer, which is more developed than animals and distinguishes our brain from theirs, it is 3mm thick. It is also divided into different lobes with areas being more localised. 
• What is the motor cortex?

  • Responsible for the generation of voluntary motor movements , it is located in the frontal lobe of the brain.
  • Each motor cortex on both hemispheres controls the opposite side for voluntary movement (left motor cortex controls right and viceversa).
  • Damage would result in less control of fine motor movements. 
• What is the somatosensory cortex?

  • Located in the Parietal lobes
  • Uses sensory information from the skin and this region produces sensations and localises to specific body regions.
  • The amount of the somatosensory cortex devoted to that part indicates the sensitivity; receptors on the face and hand take up most (50% of the entire cortex).
• What is the visual cortex?

  • It is located in the occipital lobe
  • The visual processing begins in the retina and nerve impulses sent to the brain via the optic nerve to the visual cortex.
  • The visual cortex spans both hemispheres and contains several different areas with each processing different types of visual information such as colour, shape and movement. 
• What is the auditory cortex?

  • Situated in the temporal cortex on both hemispheres, this is concerned with hearing.
  • The auditory pathway begins in the inner ear, where sound waves are converted to nerve impulses, which travel via the auditory nerve to the auditory cortex of the brain.
  • The cortex then causes an appropriate response to the speech based information.
  • Damage to this area will result in partial hearing loss, the more damage, the more the extensive the loss of hearing. 
• What is Broca's area?

  • Discovered small region in the left hemisphere of the brain responsible for speech reproduction and grammar.
  • He found that damage can result in Broca’s aphasia which means that it is characterised by slow speech and lacking in fluency.
  • Broca discovered Tan who could understand speech but could not do it in speech or writing. He was called tan as it was the only syllable possible to produce.
• What is Wernicke's area?

  • Carl Wernicke discovered an area responsible for language comprehension.
  • This is in the left temporal lobe.
  • Any damage can result in Wernicke’s aphasia, where patients had problems understanding speech but they could produce language.
  • However, the speech would be characterised through nonsense and words without meaning due to lack of understanding.  
• Supporting evidence for language centres?

  • First of all, there is a wealth of evidence to support the idea that many functions are localised, especially the language centres of the brain.
  • Peterson et al (1988) used brain scans to demonstrate how Wernicke’s area was active during a listening task (requiring comprehension of speech) and Broca’s area for a reading task.
  • This suggested that areas of the brain does have different functions
  • Therefore, there is supporting evidence for the role of localisation of functions in the brain, which means that it has validity.
• Contradicting evidence of Lashley's rat study?

  • However there is contradicting evidence for high cognitive functions which relate to the process of learning, it is not localised but distributed in a more holistic way in the brain.
  • Lashley trained rats to find their way through a maze.
  • He then took out 10-50% of areas of the brain to see if he could erase the original memory of the maze, regardless of the size or location of the lesion.
  • It suggests that learning is far too complex to be simplified into a single area of the brain and instead it should be viewed as many different parts of the brain involved.
  • This suggests that localisation of function is far too reductionist. 
• Criticism involvng individual differences in the language centres?

  • Another criticism is that they found individual differences in the language centres.
  • There has been found to be a different pattern of activation to various language activities from individual to individual.
  • There has also been found to be major gender differences in the language centres as found in Harasty et al (1997).
  • They found that women have a larger use of Broca’s area and Wernickes’ area due to larger use of language than men.
  • This indicates individual differences in the localisation of function and may not be generalised to everyone in the same way. 
• Contradicting evidence from the idea of plasticity?

  • There is more contradicting evidence from the idea of plasticity. When the brain has become damaged through an accident or an illness, the brain seems able to attempt to restore lost function by reorganising itself.
  • Although this does not happen every time, there are several real life cases of stroke victims recovering their lost ability which was seen as lost as part of the illness prior.
  • Therefore, function can change suggesting that localisation of function in certain areas of the brain can change, which is a massive issue.