localisation of function in the brain

Question 1

localisation versus holistic theory

Answer 1

• in the 19th century, scientists such as Broca and Wernicke discovered that specific areas of the brain are associated with particular physical and psychological functions
• before this, scientists supported the holistic theory of the brain, that all parts were involved in processing of thought and action
• Broca and Wernicke argued for localisation of function, the idea that different parts perform different tasks and are involved with different parts of the body
• follows then that if a certain area of the brain was damaged through illness or injury, the function associated with that area would also be affected

Question 2

hemispheres of the brain

Answer 2

• main part of brain (cerebrum) is divided into 2 symmetrical halves (left and right hemispheres)
• some physical and psychological functions are controlled or dominated by a particular hemisphere (lateralisation)
• generally, activity on the left hand side of the body is controlled by the right hemisphere and activity on the right hand side of the body is controlled by the left hemisphere

Question 3

the motor, somatosensory, visual and auditory centres

Answer 3

• cerebral cortex is outer layer of both hemispheres
• divided into frontal lobe, temporal lobe, parietal lobe and occipital lobe
• at the back of the frontal lobe is the motor area, controls voluntary movement on the opposite side of the body. damage to this area may cause loss of control over fine movements
• at the front of both parietal lobes is the somatosensory area, separated from motor area by central sulcus. this represents sensory information from the skin. the amount of area devoted to a particular body part denotes its sensitivity
• in the occipital lobe is the visual area, eyes send information from right visual field to left visual cortex and vice versa
• temporal lobes house the auditory area, analyses speech-based info. damage may produce partial hearing loss

Question 4

the language centres of the brain

Answer 4

Broca -
- identified small area in left frontal lobe responsible for speech production.
- damage to Broca’s area causes Broca’s aphasia (speech that is slow, laborious and lacking in fluency)
- people with Broca’s aphasia have trouble with conjunctions and prepositions

Wernicke -
- described people who had no trouble producing language but severe difficulties understanding it, and the speech they produced was fluent but meaningless
- identified a region (Wernicke’s area) in left temporal lobe, responsible for language understanding
- results in Wernicke’s aphasia when damaged, these people produce nonsense words (neologisms)

Question 5

evaluation strength - evidence from neurosurgery

Answer 5

• damage to areas of the brain has been linked to mental disorders
• neurosurgery is last resort for treating some mental disorders, targets specific areas of the brain that may be involved
• eg. cingulotomy isolates region called cingulate gyrus which has been implicated in OCD
• Darin Dougherty reported on 44 people with OCD who had had a cingulotomy
• 32 weeks post-op, 30% had met criteria for successful response to surgery and 14% for partial success
• success of procedures suggests that behaviours related to certain mental disorders can be localised

Question 6

evaluation strength - evidence from brain scans

Answer 6

• supports idea that many everyday brain functions are localised
• Steven Peterson used brain scans to show how Wernicke’s area was active during a reading task
• review of LTM studies by Buckner and Petersen revealed that semantic and episodic memories reside in different parts of prefrontal cortex
• objective methods for measuring brain activity have provided scientific evidence that brain functions are localised

Question 7

evaluation limitation - language localisation questioned

Answer 7

• language may not be localised to just Broca’s and Wernicke’s areas
• Dick and Tremblay found that only 2% of modern researchers think that language in the brain is completely controlled by these 2 areas
• advances in brain imaging such as fMRI mean that neural processes can be studied with more clarity than before
• seems that language distribution is distributed more holistically than originally thought
• language streams have been identified, as well as subcortical regions such as the thalamus
• suggests that language may be organised more holistically in the brain, contradicting the localisation theory