Hemispheric Lateralisation and Split Brain Research

Hemispheric Lateralisation and Split Brain Research

1. LATERALISATION

   • The brain is split into two equal symmetrical parts
     • Idea that the two halves of the brain are functionally different and certain mental processes are controlled by one hemisphere rather than the other.
   • The brain is contralateral
     • The left side of the body is controlled by the right side of the brain and vice versa
   • LEFT HEMISPHERE
     • Language
       • Two main centres for language are only in the LH
         • Broca's area in the left frontal lobe
         • Wernicke's area in the left temporal lobe
         • If someone has a stroke on the left side of their brain, the right side of the body and speech is affected.
   • RIGHT HEMISPHERE
     • Dominant in recognising emotions in others and spatial information
   • VISION
     • Both contralateral and ipsilateral
       • Each eye receives light from the left visual field and the right visual field
         • LVF is connected to RH
         • RVF is connected to LH
   • AO3
     • Research shows that even in connected brains the two hemispheres process information differently
       • Gereon Fink et al (1996)
         • Used PET scans to identify which brain areas were active during a visual processing task. When asked to attend to global elements of an image the RH was more active.
           • When asked to point out finer details, LH dominated.
     • Idea of LH as the analyser and RH as synthesiser may be incorrect.
       • Nielsen et al (2013)
         • Analysed over 1000 brain scans and found that people used certain hemispheres for certain tasks, but no evidence of a dominant side.

2. Localisation refers to the fact that some functions are governed by specific areas in the brain.

3. SPLIT BRAIN RESEARCH

   • Series of studies beginning in 1960 involving people with epilepsy who had surgical separation of the hemispheres of their brain.
   • Sperry (1968)
     • Devised a system to study how two separated hemispheres deal with speech and vision
       • Eleven people with split brain operation studied with a special set up in which an image was projected.
         • Image projected to p. RVF.
           • In a normal brain, the corpus callosum would share the information across both hemispheres giving a complete picture
           • FINDINGS
             • When a picture was shown to RVF, the participant could describe what was seen, but could not describe it if it was shown to the LVF.
               • This is because in the connected brain messages from the RH are relayed to the language centres in LH. This is not possible in split brain.
                 • Although they could not give verbal labels to objects in LVF, they could select a matching object using their left hand
     • CONCLUSION
       • Observation showed how certain functions are lateralised in the brain and support the view that the LH is verbal and RH is silent but emotional.
   • AO3
     • Support from recent research
       • Gazzaniga (1989) showed that split brain participants actually perform better on certain tasks.
         • E.G Faster at identifying the odd one out of an array of similar objects.
           • LH cognitive strategies are not "watered down" by the RH
     • Casual relationships between the two are hard to establish
       • Compared with a neurotypical control in original experiment, however none of these people had epilepsy which caused a confounding variable.