Brain localisation

• Localisation of function is the idea that different parts of the brain perform different functions
• When a part of the brain is involved with a certain function, that means that function is localised to that area
• The brain is divided into two halves called hemispheres
• The left and right hemispheres are divided by a small gap
• The left and right hemisphere are connected with the corpus callosum
• The corpus callosum is a bundle of axons enabling communication between the left and right hemispheres
• Hemispheric lateralisation - the left and right hemispheres perform different functions
• Left hemisphere - language skills
• Right hemisphere - spatial skills
• Contralaterally organised functions - the right hemisphere controls the left side of the body, and vice versa
• Contralaterally organised functions - vision, movement, touch
• Functions that are not contralaterally organised - hearing, smell, taste
• Evidence for hemispheric lateralisation comes from split brain research, on patients that have had their corpus callosum severed
• Split brain patient's two hemispheres can no longer communicate with each other
• Split brain research process:

  Observer presents stimulus to patient's left or right hemisphere, and are asked to respond to the stimulus

  They have to describe or point with their hand to the stimulus they were just shown

  If the function isn't hemispherically lateralised, they should be able to perform the function, regardless of whether the stimulus is presented to the right or left

  If the function is lateralised, the patient will only be able to perform the function if the stimulus is presented to the corresponding hemisphere
• Sperry ( 1968 ) Presented images to the patients left or right hemispheres. He found that if they were asked to point to one of four pictures to identify which matched the image, they could regardless of the hemisphere it was presented to. If they were asked to verbally describe the image, they only could if it was presented to their left hemisphere
• Sperry ( 1968 ) - split brain patients could only verbally describe an image if it was presented to their left hemisphere
• Sperry ( 1968 ) found that language is hemispherically lateralised to the left hemisphere
• Limitations of split brain research:

  May lack generalisability - only small amount of patients with severed corpus callosum

  Brain abnormalities may be a confounding variable in research

  Not all findings on hemispheric lateralisation have been replicated - more recent studies show that not all aspects of language are controlled by the left hemisphere

  There are case studies that are exceptions to the theory
• Case study exception to split brain research - patient EB :

  Had his left hemisphere removed when he was 2 years old, lost his language skills

  He regained these skills through rehabilitation, which wouldn't be possible if language skills were lateralised to the left hemisphere

  Danelli conduced a case study on EB, with verbal questions and MRI, comparing images of EB's brain to controls.

  It was found that lateralised features can be taken over by the right hemisphere
• Motor cortex - controls our body movements, organised contralaterally
• Somatosensory cortex - processes our feeling of touch, organised contralaterally
• Auditory cortex - responsible for processing sound, not organised contralaterally
• Visual cortex - processes vision, organised contralaterally
• Broca's area - enables us to produce language, lateralised to left hemisphere
• Wernicke's area - understand spoken and written language, lateralised to left hemisphere
• Six structures on the cortex ( the brain's outer surface ) : Motor cortex

  Somatosensory cortex

  Auditory cortex

  Visual cortex

  Broca's area

  Wernicke's area
• Aphasia - when people lose the ability to produce or understand language
• Two types of aphasia:

  Broca 's aphasia

  Wernicke 's aphasia
• Broca 's aphasia - the inability to produce language
• Wernicke 's aphasia - the inability to understand language
• Support for the theory of brain localisation - post mortem examinations:

  Can see which part of the brain are damaged, researchers found that damage in similar areas lead to similar symptoms
• Limitations of the theory of brain localisation:

  The idea may be over simplified, a function sometimes uses multiple brain regions

  Ignores the importance of communication between brain regions, when the connections between regions are damaged, functions can also be impaired

  Ignores individual differences in brain organisation