Localisation of function in the brain

• holistic theory replaced by localisation theory in recent years

  scientists in the early 19th century supported the holistic theory that all parts of the brain were involved in processing thought and action. but 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.
• what two halves is the brain divided into?

  the left and right hemisphere
• the brain is lateralised:

  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
• the outer layer of the brain is called the cerebral cortex
• the cerebral cortex is like a 'tea cosy' covering the inner parts of the brain. it is about 3mm thick and is what separates us from lower animals as it is highly developed. the cortex appears grey due to the location of cell bodies- hence the phrase 'grey matter'
• the cortex of both hemispheres is divided into four lobes: frontal, parietal, occipital and temporal)
• where is the somatosensory area?

  at the front of the parietal lobes
• where is the visual area?

  in the occipital lobe at the back of the brain
• where is the auditory area?

  in the temporal lobe
• what four lobes is the brain divided into?

  frontal, parietal, occipital and temporal
• motor area

  at the back of the frontal lobe (both hemispheres). 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 (touch, heat, pressure, etc). the amount of somatosensory area devoted to a particular body part denotes its sensitivity.
• visual area

  in the occipital lobe at the back of the brain. each eye sends information from the right visual field to the left visual context, and from the left visual field to the right visual cortex. so damage to the left hemisphere, for example, can produce blindness in the right visual field of both eyes
• 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
• what is Broca's area associated with?

  speech production
• when did Broca identify Broca's area?

  the 1880s
• where is Broca's area located?

  the left frontal lobe
• what does damage to Broca's area cause?

  broca's aphasia, which is characterised by speech that is slow, laborious and lacking in fluency. Broca's patients may have difficult finding words and naming certain objects. they also have difficulty with prepositions and conjunctions (e.g. and, the)
• what is wernicke's area associated with?

  language comprehension
• when did wernicke identify wernicke's area?

  the 1880s
• where is wernickes area located?

  the back of the temporal lobe
• what does damage to wernicke's area cause?

  wernicke's aphasia. patients produce language but have problems understanding it, so they produce fluent but meaningless speech. patients will also often produce nonsense words (neologisms) as part of the content of their speech.
• neologisms

  nonsense words attributed with wernicke's aphasia
• Strength: case study support:

  Unique cases of neurological damage support localisation theory, such as the case of Phineas Gage who received serious brain damage in an accident. Gage survived but the damage to his brain affected his personality- he went from someone who was calm and reserved to someone quick-tempered, rude and 'no longer Gage'. The change in Gage's temperament following the accident suggests the frontal lobe may be responsible for regulating mood
• Limitation: contradictory research

  The work of Lashley suggests higher cognitive functions (e.g. learning processes) are not localised but distributed in a more holistic way in the brain. Lashley removed between 10% and 50% of the cortex in rats learning a maze. No one area was more important than any other in terms of the rats' ability to learn the maze. As learning required every part of the cortex rather than just particular areas, this suggests learning is too complex to be localised and involves the whole of the brain
• Limitation: neural plasticity is a challenge to localisation

  When the brain had become damaged (e.g. through illness or accident) and a function has been compromised or lost, the rest of the brain is able to reorganise itself to recover the function. Lashley called this the law of equippability- what happens is that other areas of the brain 'chip in' so the same neurological action can be achieved. Although this does not happen every time, there are several documented case studies of stroke victims recovering abilities seemingly lost as a result of the illness
• Strength: brain scan evidence

  Studies have used brain scans to show activity in Wernicke's area during a listening task and in Broca's area during a reading task, suggesting these areas of the brain have different functions. Also, a study of long-term memory by Tulving et al. revealed semantic and episodic memories are located in different parts of the frontal cortex. There now exists a number of sophisticated methods for measuring activity in the brain, providing sound scientific evidence of localisation of function