Localisation Of Function

• Holistic theory of the brain


  Before scientists such as Broca and Wernicke, and the study of Phineas Gage, scientists generally held a holistic theory of the brain, that all parts of the brain were involved in thought and action.
• Localisation of function


  The theory that different parts of the brain are responsible for specific behaviours and processes or activities. Supported by Broca and Wernicke.
• Hemispheres of the brain


  The main part of the brain (cerebrum) is divided into two symmetrical halves, the left and right hemispheres. Some physical and psychological functions are controlled or dominated by a particular hemisphere, this is called lateralisation. Generally, activity on the left half of the body is controlled by the right hemisphere, and the left hemisphere controls the right. Language is connected to the left hemisphere.
• The four lobes of the cerebral cortex


  The cortex of both hemispheres is divided into four lobes. The frontal lobe, the parietal lobe, the occipital lobe and the temporal lobe. Each lobe is associated with different functions.
• The Frontal Lobe


  At the back of the frontal lobe is the motor area, responsible for voluntary movement on the opposite side of the body. Damage to this area causes loss of control of fine movements.

  
• The parietal lobe


  at the front of both parietal lobes is the somatosensory area separated from the motor area by the central sulcus. It is where sensory information from the skin is represented. The amount of somatosensory area devoted to a particular body part denotes its sensitivity, e.g. receptors for our hands and face occupy over half of the somatosensory area.

  
• Occipital Lobe



  In the occipital lobe at the back of the brain is the visual area, each eye sents information from the right visual field to the left visual cortex and from the left visual field to the right visual cortex. Meaning daage to the left hemisphere can produce blindness in the right visual field for both eyes.

  
• Temporal lobe



  The temporal lobes contain the auditory areas, responsible for analysing speech-based information. Damage may produce partial hearing loss. The more extensive the damage, the more extensive the loss. In addition, damage to a specific area of the temporal lobe, the Wernickes area, may affect the ability to comprehend language.

  
• Brain Areas

  
• Broca's Area


  In the 1880s, Paul Broca, a surgeon, identified a small area in the left frontal responsible for speech production. Damage to this area causes Brocas aphasia which is characterised by slow, laborious speech that lacks fluency. Broca's most famous patient 'Tan' could only say the word 'Tan'. People with Broca's aphasia have difficulty with prepositions and conjuctions.
• Wernickes area


  Karl Wernicke identified Wernicke's area around the same time as Broca. Wernicke's area in the left temporal lobe is responsible for language understanding. When damaged it results in Werneckie's aphasia, characterised by nonsense words as part of their speech.
• Supporting Evidence for localisation of function


  Damage to areas of the brain has been linked to mental disorders. Neurosurgery is a last resort method for treating some medical disorders, targeting areas of the brain which may be involved. Cingulotomy involves isolating the cingulate gyrus which has been implicated in OCD. Dougherty et al (2002) found 44 people who went through cingulotomy 30% met the criteria for a successful response to surgery and 14% had a partial response. The success suggests these behaviours associated with serious mental disorders may be localised.
• Evidence from brain scans to support LOF


  Evidence from brain scans supports the idea that many everyday functions are localised. Petersen et al (1988) used brain scans to show how Wernicke's area was active during a listening task and Broca's area was active during a reading task. Tulving et al. (1994) found semantic and episodic memories reside in different parts of the prefrontal cortex. Therefore objective methods for measuring brain activity have provided scientific evidence that many brain functions are localised.
• Counterpoint to support for LOF


  Karl Lashley (1950) removed 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 rat's ability to learn the route. The process of learning seemed to require every part of the cortex, rather than just one area. This suggests that higher cognitive processes, such as learning, are distributed in a more holistic way.
• Counterpoint to language LOF


  sLanguage may not be localised just to Broca's and Wernicke's area. Dick and Trembly (2016) found only 2% of modern researchers think language is completely controlled by Broca's and Wernicke's. Advancements such as fMRIs mean that we can study neural processes with more clarity. It seems language function is distributed more holistically. Language streams have been identified across the cortex, including in the right hemisphere, and subcortical regions like the thalamus. Suggesting language may be organised more holistically.
• Case study evidence for LOF


  Unique cases of neurological damage support LOF. For example, Phineas Gage had a meter-length metal rod fired through his left cheek, skull and out the top of his head, taking with it a portion of his brain and most of his left frontal lobe. The damage to his brain changed his personality and behaviour from calm and reserved to quick-tempered and rude. Suggesting the frontal lobe may be responsible for mood.