Hemispheric lateralisation; Split brain research

Hemispheric lateralisation

• The ability to reproduce and understand language, for most people, is controlled by the left hemisphere
• This suggests that language is subject to hemispheric lateralisation. The specialised areas associated with language are found in only one of the brains' hemisperes
• Whether other neural processes may be organised in this way was investigated in a series of ingenious experiments conducted by Sperry

Split-brain studies

• Sperry's studies involved a unique group of individuals, all who had undergone a commissurotomy (the corpus callosum which connect the two hemispheres were cut down the middle in order to control frequent severe epileptic seizures)
• Main communication link between the two hemispheres was removed
• Allowed Sperry to see the extent to which the two hemispheres were specialised to certain functions. And whther the hemispheres performed tasks independently of one another
• Procedure
  • An image or word could be projected to a patient's right visual field (processed by the left hemisphere) 
  • And the same, or different, image could be projected to the left visual field (processed by the right hemisphere)
  • In the 'normal' brain, the corpus callosum would immediately share the information between both hemispheres, giving a complete picture
  • However, presenting the image to one hemisphere of a split brain patient meant that the info couldn't be conveyed from that hemisphere to the other
• Key findings
  • Describing what you see:
    • When a picture of an object was shown to a patient's right visual field, the patient could easily describe what was seen
    • If the same picture was shown to a patient's left visual field, the patient could not easily describe what was seen
    • This is due to the fact there are no language centres in the right hemisphere of the brain
    • …