localisation of function in the brain

• localisation theory- the idea that specific areas of the brain are linked with specific physical and psychological functions. If an area of the brain is damaged through illness or injury, the function associated with that area is also affected
• lateralisation refers to some physical and psychological functions are controlled by either the left or right hemisphere. For example, the left side of the body is controlled by the right hemisphere and the right side of the body is controlled but the left hemisphere
• the cerebral cortex is 3mm thick and is what seperates us from lower animals as it is highly developed. It appears grey due to the location of cell bodies
• the 4 lobes of the cerebral cortex are:

  • motor area- back of the frontal lobes, controls voluntary movement, damage may result in loss of control over fine motor movements
  • somatosensory area- front of parietal lobes, processes sensory information from skin
  • visual are- in occipital lobe at back of brain, each eye send info from the right visual field to left visual cortex (and vice versa)
  • auditory area- in temporal lobe, analyses speech based info, damage may produce hearing loss
• the 2 language areas are:

  • broca's area
  • wernicke's area
• Broca's area is in the left frontal lobe and 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 findings words and naming certain objects
• Wernicke's area is located in the left temporal lobe and damage to this area causes Wernicke's aphasia which is characterised by being able to 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
• One strength of localisation theory is there is support from neurosurgery. Neurosurgery is used to test mental disorders. Dougherty et al. studies 44 people with OCD who has a cingultomy. At follow up, 30% met the criteria for successful response and 14% for partial response. The success of such procedures strongly suggests that behaviours associated with serious mental disorders may be localised
• One strength of localisation theory is there is evidence to support it by brain scan. Petersen et al. used brain scans to show activity in Wernicke's area during a listening task and in Broca's area during a reading task. Also, a study of long term memory by Tulving et al. revealed semantic and episode memories are located in different parts of the prefrontal cortex. There now exists a number of sophisticated and objected methods for measuring activity in the brain, providing sound scientific evidence of localisation of function
• One limitation of the language centre is that it has been questioned. Dick and Tremblay found that very few researchers still believe language is only in Broca's and Wernicke's area. Advanced techniques like fMRI have identified 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