Localisation of function

• Holistic theory replaced by localisation theory in recent years


  Scientists in the early 19th century supported the holistic theory that all parts of the brain were involved in processing thought and action. 

  But specific areas of the brain were later linked with specific physical and psychological functions (localization theory).

  If an area of the brain is damaged through illness or injury, the function associated with that area is also affected.
• Brain is divided into two hemispheres and lateralised. 


  Brain is divided into two halves - the left and right hemispheres. Lateralisation - some physical and psychological functions are controlled by a particular hemisphere. 

  Generally, the left side of the body is controlled by the right hemispheres; the right side of the body by the left hemisphere.
• Outer layer of brain is called the cerebral cortex


  The cerebral cortex is like a ‘tea cosy’ covering the inner parts of the brain. It is about 3mm thick and is what separates us from lower animals as it is highly developed. 

  The cortex appears grey due to the location of cell bodies - hence the phrase ‘grey matter’.
• Cortex of both hemispheres is divided into four lobes

  • Frontal
  • Parietal
  • Occipital
  • Temporal
• Motor area - back of the frontal lobe


  Controls voluntary movement. Damage may result in loss of control over fine motor movements.
• Somatosensory area - front of parietal lobes.


  Processes sensory information from the skin (touch, heat, pressure, etc). The amount of somatosensory area devoted to a particular body part denotes its sensitivity.
• Visual area - occipital lobe.


  Each eye sends information from the right visual field to the left visual cortex, and vice versa. So damage to left hemisphere, can produce blindness in the right visual field of both eyes.
• Auditory area - temporal lobe. 


  Analyses speech-based information. Damage may produce partial hearing loss - the more extensive the damage, the more serious the loss.
• Broca's area - speech production. 


  Identified in the 1880s, in the left frontal lobe.

  Damage to this area causes Broca's aphasia which is characterised by speech that is slow, laborious and lacking in fluency. Broca's patients may have difficulty finding words and naming certain objects.

  Patients with Broca's aphasia have difficulty with prepositions and conjunctions.
• Wernicke's area - language comprehension. 


  Identified in the 1880s, in the back of the temporal lobe.

  Patients produce language but have problems understanding it, so they produce fluent but meaningless speech.

  Patients with Wernicke's aphasia will often produce nonsense words (neologisms) as part of the content of their speech.
• A limitation of localisation theory is the existence of contradictory speech. 


  The work of Lashely suggests higher cognitive functions are not localised but distributed in a more holistic way in the brain. Lashley removed between 10% and 50% of the cortex in rats and learning a maze. No one area was more important than any other in terms of the rats' ability to learn the maze. As learning required every part of the cortex rather than just particular areas, this suggests learning is too complex to be localised and involves the whole of the brain.
• Another limitation is that neural plasticity is a challenge to localisation theory. 


  When the brain has become damaged and a function has been compromised or lost, the rest of the brain is able to reorganise itself to recover the function. Lashley called this the 'law of equipotentiality' - what happens is that other areas of the brain 'chip in' so the same neurological action can be achieved. Although this does not happen every time, there are several documented case studies of stroke victims recovering abilities seemingly lost as a result of the illness.
• A strength of localisation theory is support from case studies. 


  Unique cases of neurological damage support localisation theory, such as Phineas Gage who received serious brain damage in an accident. Gage survived but the damage to the brain affected his personality - he went from someone who was calm and reserved to quick-tempered, rude and 'no-longer' Gage. The change in temperament following the accident suggests the frontal lobe may be responsible for regulating mood.
• Another strength of localisation theory is support from neurological evidence. 


  Surgically removing or destroying areas of the brain to control aspects of behaviour was developed in the 1950s by Freeman - though these early attempts were brutal and imprecise. Dougherty reported on 44 OCD patients who had a cingulotomy. At a 32-week follow-up, one-third met the criteria for successful response to surgery and 14% for partial response. The process of such procedures strongly suggests that symptoms and behaviours associated with serious mental disorders are localised.