A03: Localisation of Function in the Brain

• Case Study Evidence for the Localisation of Function in the brain:

  Tan was a patient of Broca's who could only say the word 'tan.' After his death, Tan's brain was examined and it was discovered that Broca's area was damaged- suggesting that this area was localised for speech production.

  Phineas Gage was injured with a railroad spike which damaged most of his frontal lobe. After the accident, Phineas' personality changed and became more rude, quick tempered and irrational. Suggested that the frontal lobe is localised for rational thought and controlled behaviour.
• Brain Scan Evidence for localisation of function:

  Peterson et al used brain scans to demonstrate how Wernicke's area was active during a listening task and Broca's area was active during a reading task- suggesting that these areas of the brain have different functions.
• Tulving et al revealed that semantic and episodic memories reside in different parts of the prefrontal cortex.
• Neurosurgical Evidence for the Localisation of Brain Function:

  The practice of surgically removing or destroying areas of the brain to control aspects of behaviour has been around since the 1950s and, in some extreme cases, it is still used today.

  Dougherty et al (2002) found that a third of 44 OCD sufferers who had part of the cingulate gyrus removed from their brain showed improvement in symptoms following the procedure. This, and similar studies of neurosurgery, shows that particular areas of the brain may be responsible for specific behaviours.
• Arguments Against the Localisation of Brain Function

  The work of Lashley suggests that cognitive functions (such as the processes involved in learning) are not localised, but distributed in a more holistic way in the brain. Lashley removed areas of the cortex (between 10 and 50%) in rats that were learning a maze. No area was proven to be more important than any other area in terms of the rats' ability to learn the maze. The process of learning appeared to require every part of the cortex, rather than being confined to one area. This suggests that learning is too complex to be localised.
• Arguments Against the Localisation of Brain Function

  Plasticity occurs when the brain has become damaged and a particular function has been compromised or lost. The rest of the brain appears to be able to reorganise itself in an attempt to recover the lost function. Lashley described this as the law of equipotentiality, whereby surviving brain circuits work together so the same neurological action can be achieved. Although this does not happen every time.