Hemispheric Specialisation & Language

• Hemispheric Specialization


  Lateralization of function in the cerebral cortex
• Methods for studying the lateralization of function

  1. Studying the effects of damage to one hemisphere

  2. Studying the effects of deactivating one hemisphere

  3. Studying normal people (or patients, particularly those in 1) using the divided visual field experimental paradigm

  4. Studying the hemispheric distribution of brain activation

  5. Studying the effects of disconnecting the two hemispheres
• Corpus callosum


  Axons bundled together that directly connect the two cerebral hemispheres
• Callosotomy


  Surgical disconnection of the two cerebral hemispheres
• Divided visual field technique


  1. Fixate on a point straight ahead

  2. Stimuli presented in left visual field are processed in right hemisphere

  3. Stimuli presented in right visual field are processed in left hemisphere

  4. Stimuli must be presented for very short time (<180ms) to prevent eye movement
• In split brain patients, stimuli processed by left hemisphere can be verbally reported, but stimuli processed by right hemisphere cannot
• Most people show left hemisphere language localization (about 90%)
• Right hemisphere function


  • Visuo-spatial problem solving
• Block design task


  • Patient attempts to recreate a design shown in a picture using blocks
  • Easy with left hand (right hemisphere) but almost impossible with right hand (left hemisphere)
• Wada test


  1. Sodium amytal injected in one carotid artery to deactivate one hemisphere

  2. Tests conducted to determine functions remaining with only the other hemisphere active

  
• Wada test and studies of split brain patients have demonstrated a functional lateralization of language