Localisation of function Flashcards
Localisation vs Holistic theory
19th century scientists Broca and Wernicke discovered area in brain associated with specific physical and psychological functions
before this, scientists generally supported the holistic theory - all parts of the brain are involved in processing thought and action
Broca + Wernicke argued for localisation of function (cortical specialisation)
- the idea that dif parts of the brain perform dif tasks and are involved w different tasks / parts of the body
- so if a certain area of the brain is damaged, the function associated would also be affected
hemispheres of the brain
The main part of the brain (cerebrum) divided into 2 symmetrical halves called left and right hemispheres
Some of our physical and psychological functions are controlled or dominated by a particular hemisphere - LATERALISATION
Activity on the left side of body is controlled by the right side of the brain and same with the other side
Language is linked on the left hemisphere
The different lobes
Cerebral cortex: the outer layer of both hemispheres. Cortex of both hemispheres is subdivided into four centres - called the ‘lobes’ of the brain the : frontal lobe, parietal lobe, occipital lobe and the temporal lobe
A lobe - is a part of an organ that is separate in some way from the rest. Each lobe is associated with different functions
Motor area
Back of the frontal lobe: MOTOR AREA - controls voluntary movement in the opposite side of the body. DAMAGE: to this area of the brain may result in a loss of control over fine movements
Somatosensory area
Front of both parietal lobes: SOMATOSENSORY AREA - separated from the motor area by a ‘valley’ called the central sulcus. The Somatosensory area is where the sensory information from the skin (related to touch/ heat , pressure) is represented.
Amount of somatosensory area devoted to a particular body part denotes its sensitivity, e.g. receptors for out face and hands occupy over half of the somatosensory area
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 from the left visual field to the right visual cortex.
Means That damage to the left hemisphere e.g. can produce blindness in part of the right visual field of both eyes.
temporal lobes
Temporal lobes house the AUDITORY AREA which analyses speech based information. Damage may produce partial hearing loss. Extensive damage to specific areas of the temporal lobe - Wernicke’s area - may affect the ability to comprehend language.
Language being lateralised
language is restricted to the left hemisphere
1880s- Broca identified a small area in the left frontal lobe responsible for speech production
damage to broca’s area = broca’s aphasia
(speech that is slow, laborious and lacking fluency - they have difficulty with prepositions and conjunctions)
Wernicke described people who had no problem producing language but severe difficulties understanding it - speech was fluent but meaningless
- due to Wernicke’s area - left temporal lobe being responsible for language
damage results in Wernicke’s aphasia - producing nonsense words (neologisms)
Strength - evidence from neurosurgery
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 (targets specific areas of the brain that could be involved)
e.g. - cingulotomy - isolating a region called the cingulate gyrus which has been implicated in OCD
Dougherty reported on 44 people with OCD who had undergone cingulotomy
At the post surgical follow up after 32 weeks around 30% had met the criteria for successful response to the surgery and 14% partial response
Success of these procedures suggests that behaviours associated with serious mental disorders may be localised
Evidence from brain scans - Strength
Strength from brain scans is it supports idea that many everyday brain functions are localised
Petersen used brain scans to demonstrate how Wernicke’s area was active during a listening task and Broca’s area active during a reading task
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 area for everyday behaviours
SO objective methods for measuring brain activity have provided sound scientific evidence that many brain functions are localised
Counterpoint to strength of brain scans
from work of Lashley - Lashley removed areas of the cortex (10% and 50%) in rats that were learning the route through a maze.
No area was proven to be more importnant than any other area in terms of the ability to learn the route
suggests that higher cognitive processes such as learning are not localised but distributed in a more holistic way in the brain.
language localisation questioned - Limitation
limit - language may not be localised just to Broca’s and Wernicke’s areas
Study by Dick and Tremblay found only “% of modern researchers think language in the brain is completely controlled by Broca’s and Wernicke’s area
Advances in brain imaging techniques - fMRI mean that neural processes in the brain can be studied with more clarity than ever before
seems that language function is distributed far more holistically in the brain than was first thought
Language streams have been identified across subcortical regions such as the thalamus
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
Case study evidence
unique cases of neurological damage support localisation theory - e.g. Phineas Gage
But there are problems with case studies - it’s difficult to make meaningful generalisations from findings of a single individual .
And conclusions drawn may depend on the subjective interpretation of the researcher
