Localisation of Function in the brain

• Localisation of function in the brain

  Localisation versus holistic theory

  Before investigations by Broca and Wernicke (and case of Phineas Gage), scientists generally supported holistic theory of the brain - all parts of brain involved in processing of thought and action. In contrast, Broca and Wernicke argued for localisation of function. Idea that diff parts of brain perform diff tasks and involved w/ diff parts of body. So if certain area of brain becomes damaged, the function associated w/ area will also be also be effected.
• Localisation of function in the brain 2

  Hemispheres of the brain and the cerebral cortex

  Divided into two symmetrical halves called left and right hemispheres. Some physical and psychological functions are controlled or dominated by particular hemisphere (lateralisation). General rule = activity on left-hand side of body is controlled by right hemisphere and vice versa. Cerebral cortex = outer layer of hemispheres. About 3 mm thick and separates us from other animals as human cortex is more developed. Appears grey due to location of cell bodies.
• Localisation of function in the brain 3

  The frontal lobe and the motor area

  At the back of frontal lobe is the motor area which controls voluntary movement in opposite side of body. Damage to this area may result in loss of control over fine movements
• Localisation of function in the brain 4

  The parietal lobe and the somatosensory area

  At front of both parietal lobes is somatosensory area (separated from motor area by central sulcus) which is where sensory info from skin is represented. The amount of somatosensory area devoted to particular body part denotes its sensitivity (e.g., receptors in our face and hands occupy over half of area).
• Localisation of function in the brain 5

  The occipital lobe and the visual area

  In back of brain is occipital lobe and visual area/cortex. Each eye sends info from right visual field to left visual cortex and vice versa. Means damage to left hemisphere can produce blindness in part of right visual field of both eyes.
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  The temporal lobe and and the auditory area

  Temporal lobes house auditory area which analyses speech-based info. Damage may produce partial hearing loss; more extensive the damage, more extensive the loss. Damage to specific area of temporal lobe (Wernicke's area) may affect ability to comprehend language.
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  The language area of the brain

  Language is restricted to left side of brain in most people. In 1880s, Broca identified a small area in the left frontal lobe responsible for speech production. Damage to Broca's area causes Broca's aphasia which is characterised to speech that is slow, laborious and lacking in fluency.
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  The language area of the brain 2

  Around same time, Wernicke identified a region (Wernicke's area) in the left temporal lobe as being responsible for language comprehension. Damage to Wernicke's area causes Wernicke's aphasia - patients often produce nonsense words (neologisms) as part of content of their speech.
• Localisation of function in the brain- evaluation

  Wealth of evidence that providing support for idea that many neurological functions are localised. Peterson et al. (1988) 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, suggesting these areas of the brain have different functions.
• Localisation of function in the brain- evaluation 2

  Contradictory evidence. Lashley (1950) suggests that higher cognitive functions, e.g., processes involving learning, are not localised but distributed in a more holistic way in the brain. Lashley removed areas of the cortex (between 10 and 50%) in rats that were learning a maze. He found that no area was proven to be more important in terms for rats' ability to learn the maze. The process of learning required every part of the cortex rather than being confined to a particular area.
• Localisation of function in the brain- evaluation 3

  Case study evidence. Unique cases of neurological damage support localisation theory such as the case of Phineas Gage - metal pole hurled through his skull, taking most of left frontal lobe w/ it. Survived but experienced changes to personality and behaviour (quick tempered and rude). Supports localisation but lacks generalisability.