Localisation of function

• What is localisation of function in the brain?

  • 19th century scientists believed the brain worked holistically meaning all parts were involved in thought and action processing
  • Localisation or cortical specialisation suggests specific functions have specific locations in the brain
• What are the 4 main brain areas and where are they located?

  • Motor cortex - frontal lobe
  • Somatosensory cortex - parietal lobe
  • Visual cortex - occipital lobe
  • Auditory cortex - temporal lobe

  
• What is the role of the motor cortex?

  • Responsible for the generation of voluntary movements
  • Located in the frontal lobe
  • Both hemispheres have a motor cortex, with one on one side controlling the muscles on the opposite side of the body
• What is the role of the somatosensory cortex?

  • Detects sensory events arising from different regions of the body
  • Located in the parietal lobe
  • Uses sensory information from the skin to produce sensations of pain and temperature which it localises to specific body regions
  • Amount of somatosensory area devoted to a particular body part depends on how sensitive it is e.g. face and hands are most sensitive so take up over half of the cortex
• What is the role of the visual cortex?

  • Visual processing begins in the retina, at the back of the eye, which sends nerve impulses to the thalamus via the optic nerve
  • Thalamus acts as a relay station, and then passes the nerve impulses on to the visual cortex
  • Information from the right visual field will be sent to the left visual cortex and vice versa
  • Located in the occipital lobe
• What is the role of the auditory cortex?

  • Sound waves from the ear's cochlea are converted to nerve impulses which travel to the auditory cortex
  • Analyses speech and audio-based information
  • Located in the temporal lobe
• What is Broca's area?

  • Paul Broca identified an area in the left frontal lobe responsible for speech production
  • Damage to this causes Broca's aphasia, characterised by speech that is slow, laborious and lacking in fluency
• What is Wernicke's area?

  • An area in the left temporal lobe responsible for understanding language
  • Damage to this area led to Wernicke's aphasia, characterised by speech that is fluent but meaningless and can sound like nonsense words (neologisms)
• What is one strength of the localisation of function theory?

  • Research support from neurosurgery: cingulate gyrus is a brain area implicated with OCD and a cingulotomy is a surgery that isolates this region
  • Dougherty et al. (2002) reported that 30% of 44 patients had a successful response to the surgery, suggesting behaviours associated with mental disorders are localised
• What is another strength of the localisation of function theory?

  • Evidence from brain scans: Petersen et al. (1988) used brain scans to demonstrate how Wernicke's area was active during a listening task and Broca's area active during a reading task
  • Buckner and Petersen (1996) revealed that semantic and episodic memories reside in different parts of the prefrontal cortex
  • Studies confirm localised areas for everyday behaviour, acting as scientific support for the idea that brain functions are localised
• What is one limitation of the localisation of function theory?

  • Contrasting evidence: Lashley (1950) removed between 10-50% of the cortexes in rats that were learning a maze route
  • Found that no area was proven to be more important than another in the learning process
  • Suggests that higher cognitive processes like learning are not localised but distributed in the brain more holistically
  • However this evidence can be dismissed due the stark differences between human brains and rats' brains, meaning it may not be appropriate to generalise
• What is another limitation of the localisation of function theory?

  • Language localisation questioned: Dick and Tremblay (2016)'s review found that only 2% of modern researchers believe language is completely controlled by Broca's and Wernicke's areas
  • Advanced brain imaging techniques like fMRIs have shopwn that language function is distributed more holistically than thought e.g. language streams have been found in subcortical regions like the thalamus
  • Suggests that language may be more holistically organised, contradicting localisation theory