localisation

• Another strength is evidence from brain scans that supports the idea that many everyday brain functions are localised. For example, Petersen et al. used brain scans to demonstrate how Wernicke’s area was active during a listening task and Broca’s area was active during a reading task. Also, a review of long-term memory studies by Buckner and Petersen revealed that semantic and episodic memories reside in different parts of the prefrontal cortex. These studies confirm localised areas for everyday behaviours. Therefore objective methods for measuring brain activity have provided sound scientific evidence that many brain functions are localised.
• However, Lashley challenged localisation theory by removing areas of the cortex in rats that were learning the route through a maze. No area was proven to be more important than any other area in terms of the rats’ ability to learn the route. The process of learning seemed to require every part of the cortex rather than being confined to a particular area. This suggests higher cognitive processes are not localised but distributed in a more holistic way in the brain.
• Localisation of function in the brain = different parts of the brain perform different tasks and are involved with different parts of the body
• The cerebral cortex is subdivided into four centres ‘lobes’- the frontal lobe, the parietal lobe, the occipital lobe and the temporal lobe.
• The back of the frontal lobe is where the motor area is located which controls voluntary movement in the opposite side of the body. Damage to this area can cause a loss of control over fine movements.
• At the front of both parietal lobes is the somatosensory area this is where sensory information from the skin is represented.
• In the occipital lobe, at the back of the brain, is the visual area . Each eye sends information from the right visual field to the left visual cortex and vice versa. This means that damage to the left hemisphere can produce blindness in part of the right visual field of both eyes.
• The temporal lobes house the auditory area which analyses speech-based information. Damage can produce partial hearing loss. Damage to a specific area- Wernicke’s area- may affect the ability to comprehend language.
• Unlike the other areas which are found in both hemispheres, language is restricted to the left side.
• Broca identified a small area in the left frontal lobe responsible for speech production. Damage to Broca’s area causes Broca’s aphasia- characterised by speech that is slow and lacking in fluency.
• Broca’s most famous patient was ‘Tan’ - so-called because that was the only word he could say.
• Wernicke identified a region in the left temporal lobe as being responsible for language understanding. Wernicke’s aphasia causes people to produce nonsense words as part of their speech (speech produced is fluent but meaningless).
• One strength of localisation theory is damage to areas of the brain has been linked to mental disorders. Neurosurgery is a last resort for treating some mental disorders. Cingulotomy involves isolating a region which has been implicated in OCD. Dougherty reported on 44 people with OCD who had undergone a cingulotomy (isolation of the cingulate gyrus-area which has been implicated in OCD). After 32 weeks, 30% had met the criteria for successful response to the surgery and 14% for partial response. This suggests that behaviours associated with serious mental disorders may be localised.
• However, language may not be localised to just Broca’s and Wernicke’s areas. Dick and Tremblay found that only 2% of modern researchers believe language is completely controlled by Broca’s and Wernicke’s areas. Advances in brain imaging techniques, mean that neural processes can be studied with more clarity. It seems that language function is distributed far more holistically than was first thought. So-called language streams have been identified across the cortex. 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.