Hemispheric Lateralisation and Split Brain research

• hemispheric lateralisation is the idea that two halves of the human brain are not exactly alike
• split brain research is a common treatment for epilepsy
• split brain research is the study of patients that had received surgery to isolate the two hemispheres of the brain from one another - enables psychologists to study hemispheres independently
• within hemispheric lateralisation each hemisphere has functional specialities for example the left hemisphere is dominant for language and speaking and the right excels at visual motor tasks
• left hemisphere = language and speaking
• right hemisphere = visual motor tasks
• we can understand the functional specialisations within the left and right hemisphere when looking at lateralisation because of the research from Broca and Wernicke - informed us about the location of language centres within the brain
• in lateralisation, hemispheres need to be able to communicate and share info
• the left hemisphere controls the right side of the body and its movements
• the right hemisphere controls the left hand side movements of the body
• hemispheres are connected by the corpus callosum
• the corpus callosum is a bundle of nerve fibres between the 2 hemispheres
• the middle bit is the corpus callosum

  
• split brain patients are individuals who have had their corpus callosum cut which separates the two hemispheres
• split brain patients had their corpus callosum cut originally for a treatment of severe epilepsy
• sperry and gazzaniga were the first to study the capabilities of split brain patients - testing capabilities within the seperated hemispheres
• aim of sperry and gazzaniga's study on split brain research

  • examine extent to which the 2 hemispheres are specialised for certain functions
• method of sperry and gazzaniga's study for split brain patients

  • image/word projected to patients left visual field (processed by right hemisphere) or right visual field (processed by left hemisphere)
  • when info was presented to one hemisphere that info was not transferred to other hemisphere (corpus callosum cut)
  • conducted 3 different experiments (describe what you see, tactile tests, drawing tasks)
• the 3 experiments sperry and gazzaniga undertook includes tactile tests, drawing tasks and what can you see tasks
• describe what you see task (1/3 experiments of sperry and gazzaniga)

  • picture presented to either left or right visual field
  • participant had to describe what they saw
• findings of describe what you see test

  • picture presented to right visual field - patient could describe what they saw which demonstrated superiority of left hemisphere when comes to language production
  • picture presented to left visual field - patient could not describe what was shown - often reported there was nothing present
• tactile test (1/3 experiments of sperry and gazzaniga)

  • object placed in patients left or right hand
  • had to describe what they felt or select similar object from series of alternative objects
• findings of tactile test

  • objects placed in right hand - patient could describe verbally what they felt or could identify test object by selecting similar appropriate object from series of alternative objects
  • objects placed in left hand - patient could not describe what they felt and only made wild guesses. could identify test object when selecting from series of objects
• drawing task (1/3 experiments of sperry and gazzaniga)

  • participants presented with picture in either left or right visual field
  • had to the draw what they saw
• drawing task findings

  • picture presented to right visual field - right hand would attempt to draw picture but was never clear as left hand - demonstrating superiority of right hemisphere for visual motor tasks.
  • picture presented to left visual field - consistently drew clearer and better pictures than right hand
• conclusion of sperry and gazzanigas experiment

  • findings highlight key differences between 2 hemispheres - left hem is dominant for speech and language - right hem is dominant for visual motor tasks
  • research indicates importance of connectivity between 2 hemispheres to allow effective functioning.
• evaluation - advantages of hemispheric lateralisation

  • increases neural processing capacity (ability to perform multiple tasks simultaneously)
  • rogers et al - domestic chicken -brain lateralisation is associated with enhanced ability to perform 2 tasks simultaneously (finding food and being vigilant to predators) - using 1 hemisphere to engage in tasks leaves other free to engage in other functions)
  • evidence for advantage as demonstrates it can enhance brain efficiency (doing 2 things)
  • limitation - research uses animals and not humans - cannot be applied to humans correctly. - consider both
• evaluation - lateralisation linking with immune functioning

  • suggested relationship between hemispheric lateralisation and immune system functioning
  • example - left hand people tend to have superior right hemispheric skills but more likely to suffer allergies and problems with immune system
  • tonnessen found significant relationship between handiness and immune disorders
  • morfit and weekes found left handed have high incidence of immune disorders in immediate family
  • suggests genetic process leading to lateralisation which may affect development of immune system
• evaluation - lateralisation changes with age

  • lateralisation of function seems to change throughout lifetime
  • lateralised patterns found in younger individuals tend to switch to bilateral patterns in healthy older adults
  • szaflarski found language became more lateralised to left hemisphere with increasing age in children but after 25 lateralisation decreased within each decade
  • limitations is that it doesnt apply equally to all age groups
• evaluation - limitation of split brain research

  • limited number of individuals used for research towards split brain
  • andrew argues many studies are presented with few as 3 participants (shouldn't be generalised to all individuals?)
  • conclusions then drawn about function of brain from individuals who either have confounding physical disorder or have less complete sectioning of 2 hemispheres than originally believed
  • limitation of split brain research as it has limited generalisability to wider population.
• evaluation key points

  • understanding increases ability to perform multiple tasks simultaneously (having 2 hemispheres)
  • genetic process leading to lateralisation affecting development of immune system
  • limitation as it does not apply equally to all age groups (changes with age)
  • limited generalisability to wider population (limited research studies relating to split brain research)