Lateralisation and split brain

• Hemispheric Lateralisation


  Some mental processes in the brain are mainly specialised to either the right or left side.

  Left - language and speech

  Right - Visual-motor tasks

  Information/communication is passed through the hemispheres
• Corpus Callosum

  A specialised bundle of nerve fibres which transmits communication between the hemispheres
• Split Brain

  When the CC is cut, there is no way of information passing from one hemisphere to another and cannot be processed in the hemisphere it originates.

  Prevents severe high levels of electrical activity that accompanies epileptic seizures
• Sperry and Gazzaniga (1967)


  Aim - study on the capabilities of separated hemispheres
• Sperry and Gazzaniga (1967)

  Method

  1. Send visual information to one hemisphere to study lateralisation

  2. Split brain patient would fixate on a dot in the centre of a screen, sending information to either the left or right visual field

  3. They couldn't see their hands but performed physical tasks
• Sperry and Gazzaniga (1967)

  Findings

  • Shown a dog in right visual field, could articulate it
  • Shown a dog in left visual field, could not articulate it
  • No language centre in the right hemisphere
  • Can respond verbally only if hemispheres are connected
• Strength

  Sperry and Gazzaniga‘s study has discovered a number of key differences between the hemispheres. They found that the connectivity between hemispheres and regions is vital, and limits the importance of localised function
• Strength - advantages of lateralisation

  • those with a superior right hemisphere being naturally gifted at maths, and more likely to be left handed, as well as having a weaker immune system
  • Tonnessen et al (1993) found a relationship between handedness and immune system problems
• Strength - Szarflarski et al (2006)

  • Found that our lateralisation changes over time. Specifically, language becoming more lateralised to the left hemisphere. Also finding that lateralisation decreases each decade - perhaps prioritising processing together functions / areas of the brain
• Weakness

  • Ppt numbers for research into hemispheric lateralisation have been significantly limited, therefore, reducing the generalisability of research into HL and conclusions cannot be drawn
• Weakness

  • Some patients had experience a greater degree of split than others, therefore, reducing internal validity of the study
  • Similarly, some patients had experience extensive drug therapy, once again compromising the internal validity