SPLIT BRAIN RESEARCH AND HEMISPHERIC LATERALISATION

• Hemispheric lateralisation is different to localisation. It refers to the brain being divided into two hemispheres that are functionally different to each other as certain processes are controlled by one hemisphere and others by the other.
• For example, language is controlled by the left side and Wernicke and Broca's area are found in the left hemisphere so we can say that language is lateralised.
• Contralateral wiring:


  The right hemisphere controls the left side of the body, and the left hemisphere controls the right side of the body.
• Contralateral and ipsilateral:


  The visual area has contralateral and ipsilateral wiring (opposite and same sides) which is a similar arrangement for auditory functions.
• Strength


  Lateralisation is a feature in the connected brain not just split brain – FINK et al used pet scans to identify which areas of the brain were active during a visual task – looking at the picture as a whole (RH) and finer detail of the picture (LH).
• Limitation


  May be distinct functions but research suggests people do not have a dominant side – found evidence for lateralisation but no dominant side – notion of left or right brained is wrong. 
• Corpus callosum


  The corpus callosum is a c-shaped nerve fiber bundle found beneath the cerebral cortex. It stretches across the midline of the brain connecting the left and right hemispheres. It also makes up the largest collection of white matter tissue found in the brain (division between the left and right hemispheres). 
• Epilepsy


  It is a neurological condition characterised by recurrent seizures which occur due to brief disturbances in the electrical functions of the brain, and it affects people of all ages. 
• SPERRY'S research into split brains


  He conducted a series of experiments beginning in the 1960s on hemispheric lateralisation. 11 epileptic patients were used who had a surgical separation of the two hemispheres, called a commissurotomy (the corpus callosum is cut to separate the hemispheres). This was done to control epileptic seizures as it removes communication between the two sides of the brain. Researchers could now look to see if the two hemispheres performed certain functions and if they performed independently of each other. Sperry was awarded a Nobel prize for his research in 1981. 
• SPERRY procedure


  A general procedure where an image/word was projected into the patient's right visual field (left hemisphere) and the same/different image was projected into the left visual field (right hemisphere). 

  The experiment involved 11 patients who had their corpus callosum disconnected to alleviate epilepsy.
• In a normal brain the corpus callosum would share the information between the hemispheres giving a complete picture. 

  However, in a split-brain patient, the information could not be conveyed from one hemisphere to another. 
• Describing what you see:

  • When a picture was shown to the RIGHT visual field split brain patients could DESCRIBE what they see. 
  • If the same object were shown to the LEFT visual field, they could not describe what they saw (nothing) but they could DRAW it. 
  • Language is processed in the LH and there are no language centres in the RH 
• Recognition by touch:

  • If the object was placed in the right hand (LH), the patient could describe what they felt verbally. 
  • If the object was placed in the left hand (RH), the patient could not describe what they felt due to there being no language centres in the RH. However, the left hand could identify an object by selecting a similar appropriate object from a series of objects. 
• Composite words:

  • If two words were presented simultaneously, the one on the left visual field would be drawn and the word in the right visual field would be spoken aloud. 
• Conclusion of SPERRY 


  Left hemisphere - speech and language

  Right hemisphere - visual processing and motor tasks