localisation of brain functioning

• Localisation of function

  In the early 19th century holistic theory suggested 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 (localisation theory). In an area of the brain is damaged through illness or injury, the function associated with that area is also affected.
• The brain is divided into two 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 hemisphere and vise versa.
• Cerebral cortex

  The cerebral cortex is like a 'tea cosy' covering the inner parts of the brain. It is about 3 mm 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.
• Cerebral cortex of both hemispheres 


  .Visual area - in the occipital lobe at the back of the brain. Each eye sends information from the right visual field to the left visual cortex and vice versa.

  .Auditory area - in the temporal lobe. Analyses speech based information. Damage may produce partial hearing loss.
• Cerebral cortex of both hemispheres 



  .Motor area - at the back of the frontal lobe. Controls voluntary movement and if damaged it can result in loss of control over fine motor movements

  .Somatosensory area - at the front of the parietal lobes. Processes sensory information from the skin. The amount of somatosensory are devoted to a particular body part denotes its sensitivity.
• language centres

  Broca's area - speech production

  Wernicke's area - language understanding
• Broca's area

  Located 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

  People with Broca's aphasia have difficulty with prepositions and conjunctions
• Wernicke's area

  Located in the left temporal lobe

  People with Wernicke's aphasia produce language but have problems understanding it, so they produce fluent but meaningless speech.

  They will often produce nonsense words as part of the content of their speech.
• Evaluation

  One strength of localisation theory is brain scan evidence to support it. Peteren used brain scans to show activity in Wernicke's area during a listening task and in Broca's area during a reading test. Also, a study of long term memory by Tulving revealed semantic and episodic memories are located in different parts of the prefrontal cortex. There now exists a number of sophisticated and objective methods for measuring activity in the brain, providing sound scientific evidence of localisation of function.
• Evaluation

  One limitation is the language model has been questioned. Dick and Temblay found that very few researchers still believe language is only in Broca's and Wernicke's area. Advanced techniques (e.g. FMRI) have identified different regions in the right hemisphere and the thalamus. This suggests that rather than being confined to a couple of key areas, language may be organised more holistically in the brain, which contradicts localisation theory.
• Evaluation

  One strength is that there is case study evidence. Unique case studies of neurological damage support localisation theory. For example, Phineas Gage who lost some of his brain when a tamping iron shot through his head which caused his personality to change. However, it is difficult to make meaningful generalisations based on a single individual and conclusions may depend on the subjective interpretation of the researcher. This suggests that some evidence supporting localisation may lack validity, oversimplifying brain processes, and undermining the theory.