Localisation of Function in the Brain

• Holistic Theory replaced by Localisation Theory

  In the early 19th century, holistic theory suggested that all parts of the brain were involved in processing thoughts and functions. 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 illness or injury, the function associated with that area is also affected.
• Brain is divided into two hemispheres and lateralised

  • 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, the right side of the body by the left hemisphere.
• Cerebral Cortex

  Covers the inner parts of the brain. It’s 3mm thick and is what seperates us from animals as it is highly developed. The cortex appears grey due to the location of the cell bodies - grey matter.
• Cerebral cortex of both hemispheres is divided into four lobes 1/2

  • Motor area- at the back of the frontal lobe, controls voluntary movement- Damage may 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 area devoted to a particular body part denotes its sensitivity.
• Cerebral cortex of both hemispheres is divided into four lobes 2/2

  • Visual area - in the ocipital lobe at the back of the brain. Each eye sends information from the right visual field to the left visual cortex, and from the left visual field to the right visual cortex.
  • Auditory area- in the temporal lobe, analyses speech-based information. Damage may produce partial hearing loss - the more extensive the damage, the more serious the loss.
• Broca’s Area

  Located in the left frontal lobe and is responsible for speech production. Damage to this area causes Broccas aphasia which is characterised by speech that is slow, laborous and lacking in fluency. People may have difficulty finding words and naming certain objects. They usually have difficulty with prepositions and conjunctions.
• Wernicke’s Area

  In the left temporal lobe and is responsible for language understanding. Damage to this areas causes Wernicke's aphasia which is characterised by fluent language production but poor language comprehension. They produce fluent but meaningless speech, may also produce neologisms as part of their speech.
• +Support from neurosurgery

  It’s used to treat mental disorders a cingulotomy involved isolating the cingulate gyrus. Dougherty 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.
• +Support from brain scan evidence

  Tulving revealed semantic and episodic memories are located in different parts of the corte. Peterson used brain scans to show activity n Wernicke’s area during a listening task and Brocha’s area during a reading task. A number of sophisticated and objective methods for measuring activity in the brain now exist which provides sound scientific evidence of localisation of function.
• -Criticism of Brain Scan Evidence

  • Lashley removed areas of the cortex (up to 50%) in rats learning the route through a maze. Leaning required the whole cortex ratter than being confined to one area. This suggests that higher cognitive processes are not localised but distributed in a more holistic way in the brain.
• -The language localisation model has been questioned.

  Dick and Tremblay found that very few researchers still believe language is only in Brocha’s and Wernicke’s area. Advanced techniques (FMRIs) have identified regions in the right hemisphere and the hypothalamus. This suggests that, rater then being confined to a couple of key areas, language may be organised more holistically in the brain, which contradicts localisation theory.