LOCALISATION OF FUNCTION

• Paul Broca and Karl Wernicke founded localisation theory in the 19th century.

  Definition - the idea that various parts of the brain are responsible for distinct functions so if areas are damaged, function will be repaired.
• This theory challenged holistic theory which contrasts localisation as it states that all parts of the brain were involved in the processing of thought and action.
• The cortex of both hemispheres is divided into four lobes (named after the bones beneath which they lie) and each lobe has a different function.
• Evidence for localisation - Phineas Cage


  In the olden days people believed the brain was holistic until the case of Phineas Cage. He was a railway worker that had an accident when a metal rod went through the left side of the brain.

  Outwardly, he appeared to function normally (walking, talking, eating) but to those who knew him said that his personality and behaviour had changed becoming rude and impatient.

  This disproved the holistic theory as if it were true, his whole brain should be damaged. This study of Phineas Cage founded the localisation theory. 
• 1. Two symmetrical halves – left and right hemispheres. 
  2. Lateralisation of function – some physical or psychological functions are controlled or dominated by a particular hemisphere. Activity on the left of the body is controlled by the right hemisphere and vice versa 
  3. Cerebral cortex – outer layer of each hemisphere which is 3mm thick 
  4. The cortex is grey (‘grey matter’) – the human cortex is far more developed than animals. 
• Four lobes:

  • Frontal lobe - Falling
  • Parietal lobe - Potatoes
  • Occipital lobe - On
  • Temporal lobe - Tom
• MOTOR AREA:


  The motor area is located at the back of the frontal lobe and controls voluntary movement in opposite sides of the body. The damage of this area may result in the loss of control over fine movements. 
• SOMATOSENSORY AREA:


  This area is located at the front of the parietal lobes and is separated from the motor area by the ‘central sulci.’ The sensory information from the skin is represented and the more sensitive the area the more space is devoted. 
• VISUAL AREA:


  The visual area is located in the occipital lobe. Each eye sends information form the right visual field to the left visual cortex and from the left visual field to the right visual cortex. Damage to the left hemisphere can produce blindness in part of the right visual field of both eyes. 
• AUDITORY AREA:


  The auditory area is in the temporal lobe. It analyses speech-based information, and any damage could cause partial hearing loss but damage to specific areas (e.g., Wernicke's area) may affect the ability to understand language. 
• BROCA'S AREA - understanding language


  The Broca’s area is in the left hemisphere of the brain. In the 1880s Broca identified a small area in the left frontal lobe responsible for speech production. Damage to this area causes Broca’s aphasia which is categorised by slow, laborious speech that lacks fluency. Anyone who suffers from Broca's aphasia can understand what they are saying but is unable to say it. 
• WERNICKE'S AREA - expressing language


  The Wernicke's area is in the left hemisphere too. In the 1880s Wernicke identified a region in the left temporal lobe responsible for language comprehension. Damage to this area causes Wernicke's aphasia which is the production of nonsense words (neologisms). Anyone who suffers from Wernicke's aphasia can talk but does not understand what they are saying. 
• Strength (1):


  ✅ Brain scan evidence of localisation – PETERSON et al (1988) used brain scan to show that Wernicke's area was active during a listening task and Broca's area was active during a reading task. TULVING et al (1994): semantic and episodic memories are stored in various parts of the prefrontal cortex. This demonstrates that the localisation theory is reliable. 
• Strength (2):


  ✅Neurological evidence in support – in 1940s (Walter Freeman) early attempts of lobotomy were brutal, imprecise, and typically involved severing connections in the frontal lobe to try and control aggression. Neurosurgery is still used today in extreme cases of OCD and depression. DOUGHERTY et al (2002) - 44 OCD patients had a cingulumotomy (lesioning of the cingulate gyrus). After 32 weeks in a follow up, 1/3 of patients had a successful response and 14% were partially successful. This suggests MH symptoms are localised to areas of the brain. 
• Strength (3):


  ✅ Case study evidence – the case of Phineas Cage supports the theory of localisation HOWEVER this case lacks population validity. 
• Weakness (1):


  ❌ LASHLEY’S research challenges localisation theory – they removed 10-50% of the cortex in rats who were learning to navigate a maze. They found that no area was more important than any other in the rat's ability to learn the maze. In conclusion, higher cognitive functions are NOT localised but spread in a more holistic way in the brain. ‘Learning’ appeared to require every part of the cortex and not confined to a particular area, challenging localisation theory HOWEVER animal studies cam not always be applied to humans as humans are more highly developed (extrapolation). 
• Weakness (2):


  ❌ Plasticity – when the brain has been damaged and a function is lost, the rest of the brain is able to reorganise itself to recover the lost function. The ‘law of equipotentiality’ means that each brain has an equal potential of doing all tasks. Plasticity challenges localisation theory as it suggests ALL parts of the brain can perform all functions.