6.3.1 Localisation of Function in the Brain & Hemispheric Lateralisation

Localisation of Brain Function 

• Localisation of brain function is where certain functions (memory, speech, language) have specific locations in the brain 
• The brain is split into two hemispheres, this is the right and left hemisphere 
• The two hemispheres are connected by the corpus callosum, which acts as a bridge between the two hemispheres and allows them to send messages and work together  
• Each hemisphere has 4 brain lobes
  • Frontal Lobe: 
    • Motor control (premotor cortex) 
    • Problem solving (prefrontal area)
    • Speech production (Broca's area) 
  • Temporal Lobe: 
    • Auditory processing
    • Language comprehension (Wernicke's area) 
    • Memory/information retrieval 
  • Parietal Lobe:
    • Touch perception (somatosensory cortex)
    • Body orientation 
    • Sensory input 
  • Occipital Lobe:
    • Sight (visual cortex)
    • Visual reception and interpretation 
• There is also the cerebellum that controls balance and coordination and the brain stem, which controls involuntary responses

Phineas Gage 

• Phineas Gage was a railroad worker in the USA, his job involved blasting dynamite to clear the path for the rail construction. 
• one day Phineas' tamping iron, which was a rod used for blasting the dynamite, went through Phineas' head when an explosion went wrong
• The rod went through Phineas' chin and out through the top of his head 
• Phineas did not lose consciousness and he could speak throughout the incident and recovery 
• He recovered well eventually after suffering from a bad infection
• Apart from losing his sight in his left eye and some scary, Phineas recovered physically well from the injury 
• However, he was changed psychogically, before the accident, Phones was described as a calm and well-mannered individual
• But, after the accident he showed, unreliable, rude and hostile behaviour 
• This supports the idea of Localisation, and the personality change can be explained by the damage to a specific area of the brain 

Hemispheric Lateralisation 

• The brain is split into two equal symmetrical parts, the right and left hemispheres
•  The brain is contralateral 
• The left side of the body is controlled by the right side of the brain and vice versa
• If someone has a stroke in the left part of the brain, it will be physically evident on the right side of the body, such as that side of the mouth will drop or weakness in the limbs on the right side of the body 
• Hemispheric lateralisation is the division of functions between the two hemispheres 
• Left Hemisphere 
  • The left hemisphere for most people is where they process language 
  • Broca and Wernicke's areas are found in the left hemisphere 
  • If someone has a stroke in the left hemisphere, their speech will likely be effected
• Right Hemisphere 
  • Dominant in recognising emotions in others 
  • Spatial information 
    • A case study conducted on a woman who had damaged the right hemisphere found that she would often get lost even in familiar locations if she didn't have verbal instructions for directions also, which supports the idea, that the right hemisphere is dominant in spatial information 

Broca's Area 

• Broca correctly identified the area of the brain responsible for speech 
• They found not all words were equal in the Broca area and they were effected differently 
• Nouns and verbs seemed be less effected but predisposition and conjunctions were no longer able to be used

Broca

• Broca was a neurologist
• One patient, named Louis Lebornge, who was the son of a school teacher, suffered from epilepsy throughout childhood 
• Although educated and a craftsman, Lebornge eventually lost the ability to speak apart from the word tan 
• He was hospitalised at the age of 30 and stayed in hospital until he died in 1861 at the age of 51
• After his death, Broca performed a post-mortem on his brain 
• He found a lesion on the left temporal lobe, this was the only damage found 
• As this was the only visible area of damage, Broca concluded that it was the area responsible for speech production, as Leborgne had developed a deficit in that area 
• The term Broca's aphasia is used today for patients who display problems producing speech 

Wernickes Area 

• Wernickes area is a separate area of language processing which has a specific function 
• Wernicke worked in a hospital in Germany 
• He found patients who had damage near the auditory cortex had specific language impairments
  • The inability to comprehend language and anomia
• However, he found that the same people did have fluent speech when they were able to access the words quickly 
• Wernicke suggested this area was important for understanding language and accessing words 

Split Brain Research 

• The human brain is contralateral
  • The left side of the brain centres and moves the right side of the body and the right side of the brain centres and moves the left side of the body
  • The right side of the brain takes the visual information from the left visual field taken from both optic nerves and the left side of the brain takes the visual information from the right visual field, again from both optic nerves 
  • However, areas for speech are only located on the left side of the brain
• The left and right hemispheres are connected by the corpus callosum
  • This connection allows for quick communication between the two hemispheres 
• Cutting the connection between the two hemispheres (the corpus callosum) seems excessive, however, this was used as a treatment for extreme epilepsy 
  • The aim of the treatment was to stop the electric seizures bouncing between hemispheres, reducing the number of fits the patient's experience
  • Patients reported very few side effects from the treatment, however, they did say that they felt like they had the strange sensation that they were two people inside one body

Sperry's Split Brain Research

• Sperry (1968) studied 11 patients who had a corpus callosotomy as treatment for their epileptic seizures  
• Sperry projected information into each visual field, controlling which information each visual field accessed
• In a series of tests, participants would be asked to either say what they saw, draw it or pick out from hidden objects
• Sperry found that information presented to the left hemisphere could be spoken, but not if it had been delivered to the right hemisphere 
• However, the information presented to the right hemisphere could be drawn or picked out from objects with the left hand 
• Sperry's research supports lateralisation and shows the hemispheres working independently 
• This research also supports localisation of function as it shows the language centres are on the left side of the brain 

Gazzaniga (1983)

• Found when participants of split-brain research, had each of their hemispheres presented with faces, the right hemisphere was more capable of recognising them
• This suggests the right hemisphere is responsible for face recognition 

Evaluation points 

• The sample of split-brain research patients was very small 
  • Results could have been due to individual participant variables as they had their brain cut and drug therapy, meaning the results may not be able to be generalised to the wider population 
• The tasks the participants had to do, lacked mundane realism, which results in low external validity
• However, split-brain research had a huge impact on the psychological understanding of the brain and individuals' identities