localisation of function in the brain

• The holistic theory was replaced by localisation theory:

  • 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)
  • If an area of the brain is damaged through injury or illness, the function associated with that area is also affected
• Brian is divided into 2 hemispheres and lateralised:

  • Lateralisation = the specialisation of the 2 hemispheres (left and right) for different functions
  • Some physical and psychological functions are controlled by a particular hemisphere
  • generally:
  • the left side of the body is controlled by the right hemisphere
  • the right side of the body is controlled by the left hemisphere
• cerebral cortex:

  • Cerebral cortex = outer layer of the brain
  • It 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)
  • It appears grey due to the location of cell bodies (hence the phrase ‘grey matter’)
• cerebral cortex of both hemispheres is divided into 4 lobes:

  • 4 lobes = frontal, parietal, occipital, temporal
  • Motor area:
  • At back of both frontal lobe on both hemispheres
  • Controls voluntary movement
  • Damage may result in loss of control over fine motor movements
  • Somatosensory area:
  • At front of both parietal loves
  • Processes sensory information from the skin (eg touch, heat, pressure)
  • Amount of somatosensory area devoted to a particular body part denotes it’s sensitivity
  • Visual area:
  • In occipital lobe
  • Each eye sends information from = right visual field to left visual cortex and left visual field to right visual cortex
  • Auditory area:
  • In temporal lobe
  • analyses speech-based information
  • Damage may produce partial hearing loss (the more extensive the damage, the more serious the loss)
• the language centres:

  • Broca’s area
  • Wernicke‘s area
• Broca’s area (speech production)

  • Identified by Broca in 1880s
  • In the left frontal lobe
  • Damage to the area causes Broca’s aphasia, characterised by:
  • speech that is slow, laborious and lacking in fluency
  • Broca’s patients at have difficulty finding words or naming certain objects
  • People with Broca’s aphasia also have difficulty with prepositions and conjunctions (eg ‘a‘, ‘the’, ‘and’)
• Wernicke’s area (language understanding)

  • Identified by Wernicke in 1880s
  • In the left temporal lobe
  • Damage to the area causes Wernicke’s aphasia, characterised by:
  • People producing language but having difficulty understanding it (they produce fluent but meaningless speech)
  • people with Wernicke‘s aphasia will often produce nonsense words (neologisms) as part of the content of their speech
• strength = localisation theory is supported by neurosurgery

  • Neurosurgery = used to treat mental disorders
  • Eg = cingulotomy involves isolating the cingulate gyrus (dysfunction of this area may be a cause of OCD)
  • Dougherty et al = studied 44 people with OCD who had a cingulotomy
  • 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
• strength = localisation theory is supported by brain scan evidence

  • Peterson et al = used brain scan evidence to show activity in Wernicke’s area during a listening task and in Broca’s area during a reading task
  • Tulving et al = long-term memory study = 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
• counterpoint to support from brain scan evidence

  • Lashley removed areas of the cortex (up to 50%) in rats learning the route through a maze
  • Learning required all of the cortex rather than being confined to a particular area
  • Suggests that higher cognitive processes (eg learning) are not localised but distributed in a more holistic way in the brain
• limitation = the language localisation model 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 (eg fMRI) have identified regions in the right hemisphere and the thalamus
  • Suggests tat rather than being confined to a couple key areas, language may be organised more holistically in the brain (contradicts localisation theory)
• extra evaluation = case study evidence

  • Unique cases of neurological damage support localisation theory
  • Eg = Phinneas Gage = lost some of his brain in an explosion and his personality changed
  • BUT = it is difficult to make meaningful generalisation based on a single individual and conclusions may depend on the subjective interpretation of the researcher
  • Suggests that some evidence supporting localisation may lack validity, oversimplifying brain processes, and undermining the theory
• Localisation of the brain: