localisation of function in the brain

• localisation of function -

  • theory that different areas of the brain are responsible for specific behaviours, processes or activities
  • broca and wernicke discovery
  • certain areas of brain becomes damages through illness or injury the function associated with that area will also be affected
  • before scientists supported holistic theory
• hemispheres of the brain -

  • main part of the brain (cerebrum) is divided into 2 symmetrical halves - right and left hemisphere
  • lateralisation = some physical and psychological functions are controlled or dominated by a particular hemisphere
  • general rule - left hand side of body is controlled by right hemisphere and activity on right hand side of body by left hemisphere
• brain lobes -

  • cerebral cortex is outer layer of both hemispheres
  • divided into 4 centres - the lobes:
  • frontal, parietal, occipital, temporal
  • lobe = a part of an organ that is separate in some way from the rest
  • each lobe in the brain is associated with different functions
• motor area -

  • back of frontal lobe in both hemispheres
  • controls voluntary movement in opposite side of body
  • damage to this area of brain may result in a loss of control over fine movements
• somatosensory area -

  • front of both parietal lobes - separated from motor area by a valley called central sulcus
  • where sensory information from the skin is represented
  • amount of somatosensory area devoted to a particular body part denotes its sensitivity - eg receptors for out face and hands occupy over half of somatosensory area
• visual area -

  • in the occipital lobe at back of brain
  • each eye sends information from the right visual field to the left visual context and from the left visual field to the right visual cortex
  • means damage to left hemisphere can produce blindness in part of the right visual field of both eyes
• auditory area -

  • temporal lobes
  • analyses speech-bases information
  • damage may produce partial hearing loss
  • more extensive the damage, the more expensive the loss
  • damage to a specific area of the temporal lobe (Wernike's area) may affect the ability to comprehend language
• language centres of the brain -

  • language restricted to left side of brain
  • Broca's area - responsible for speech production - damage causes Broca's aphasia which is characterised by speech that's slow, laborious and lacking in fluency - difficulty with prepositions and conjunctions
  • Wernicke's area - area in left temporal lobe responsible for language understanding - no problems producing language but difficulty understanding - damage causes Wernicke's aphasia - produce nonsense words as part of speech content
• evaluation of localisation theory: evidence from neurosurgery (strength) -

  • P: damage to areas of the brain has been linked to mental disorders
  • E: neurosurgery last resort used for treating mental disorders
  • E: Dougherty et al (2002) reported on 44 people with OCD who had undergone a cingulotomy (involves isolating region called the cingulate gyrus which is implicated in OCD) - after 32 weeks 30% met criteria for successful response to surgery + 14% for partial response
  • L: success of procedures suggests behaviours associated with serious mental disorders may be localised
• evaluation of localisation theory: evidence from brain scans (strength) -

  • P: supports idea that many everyday brain functions may be localised
  • E: Petersen et al (1988) used brain scans to demonstrate how Wernicke's area was active during reading task + Broca's area was active during reading tasks
  • E: Buckner and Petersen (1996) reviewed long term memory studies - revealed semantic and episodic memories reside in different parts of prefrontal cortex
  • objective methods for measuring brain activity have provided sound scientific evidence that many brain functions are localised
• evaluation for localisation theory: evidence from brain scans (counterpoint) -

  • P: challenge to localisation theory comes from Lashley (1950)
  • E: removed areas of cortex (between 10-50%) in rats learning the route through a maze - no area was proven to be more important than any other area in terms of rats ability to learn the route
  • E: process of learning required every part of cortex rather than confined to particular area
  • L: suggests that higher cognitive processes such as learning are not localised but distributed in a more holistic way in the brain
• evaluation of localisation theory: language localisation questioned (limitation) -

  • P: language may not be localised just to Broca's and Wernicke's areas
  • E: Dick and Tremblay (2016) review found 2% of modern researchers think language is only controlled by Broca and Wernicke's areas
  • E: advances in brain imaging techniques (eg fMRI) mean better brain studies - seems language function is distributed far more holistically - language streams identified across cortex, brain regions in right hemisphere, subcortical regions such as thalamus
  • L: suggests language organised more holistically