Evaluation of Localisation of function in the brain: Flashcards
P:Evidence from case studies of individuals with brain damage seem to indicate that there is localisation of function in the brain.
E:For example, the case study of Leborgne (‘Tan’) suggests that there is a specific area of the brain responsible for speech production. Leborgne lost the ability to speak and could only utter the word ‘Tan’.
When Broca conducted a post-mortem on Leborgne’s brain, he found a lesion on the frontal lobe in the left hemisphere, which he named Broca’s area.
C:This supports localisation of function in the brain because if other parts of the brain were involved in speech production, then there would not have been a loss of speech function in Leborgne.
+However, this research can be criticised because it is a case study involving one unique individual, making it difficult to generalise the findings to others.
P:However, language production may not be confined to Broca’s area alone.
E:Dronkers et al. (2007) re-examined the preserved brain of Leborgne (Tan), using MRI brain imaging to reveal that other areas besides Broca’s area could have also contributed to his reduced speech ability – the lesion extended far deeper than Broca was able to report.
C:Therefore, although lesions to Broca’s area alone can cause temporary speech disruption, they do not usually result in severe and persisting disruption of spoken language.
+This suggests that language and cognition are far more complicated than once thought and involve networks of brain regions rather than being localised to specific areas.
P: The holistic theory of brain function argues that localisation of function is largely incorrect.
E:The ‘holistic theory’ of brain function is supported by Lashley’s (1950) research. He trained rats to run through a maze and then removed (lesioned) specific areas of their cortex to investigate the extent to which memory is localised. He did not find any specific area involved in memory, it appeared to be stored all over the brain.
C:This therefore casts doubt on the idea that specific areas perform specific functions. Lashley did argue, however, that basic motor and sensory functions were localised, but that higher mental (i.e. cognitive) functions were not
+ It is difficult to extrapolate his findings to humans as there are key physiological differences between a rat and human brain.
Furthermore, maze running involves many parts of the brain e.g. vision (remembering the sight of correct pathways) and spatial sense (remembering the direction to turn). If one type of cue is eliminated, there are many others remaining, allowing the rat to guide itself to the end of the maze.
P:On the other hand, the fact that rehabilitation can help individuals to overcome brain trauma suggests that there is no localisation of function.
E:If there were task-specific areas, then there would be no brain plasticity. Lashley claimed that intact areas of the cortex could take over responsibility for specific cognitive functions following damage to the area normally responsible for that function (his equipotentiality theory).
For example, the case of E.B., who had his left hemisphere removed at 2½, regained most of his language abilities – at age 17 his language appeared almost normal in everyday life in terms of vocabulary and grammar compared against healthy controls
C:This therefore suggests that the right hemisphere – through intensive rehabilitation - has the ability to take on the functions of the left hemisphere, compensating for any functions that may have been lost.
+However, E.B. did not fully recover all lost language functions (there were some subtle grammatical problems; difficulties picture-naming), which suggests that there is some localisation of language function in the left hemisphere.
P: However, research suggests that what might be more important is how brain areas communicate with each other, rather than the idea that specific brain regions control a particular cognitive function.
E:Wernicke claimed that although different regions of the brain had different specialist functions, they are interdependent - in order to work they must interact with each other.
For example, complex behaviours such as language, reading and movement are built up gradually as a stimulus enters the brain, then moves through different structures before a response is produced.
C:Therefore, damage to the connection between any two points (e.g. arcuate fasciculus) in this process results in impairments that resemble damage to the localised brain region associated with a specific function.
+Ultimately, the brain is so complex that no one part acts independently of the rest, so strict localisation is impossible and it is reductionist to view brain function in this way.
P:There are individual differences in language areas in that the pattern of activation observed in response to various language activities can vary from one person to the next.
E:For example, in a study of silent reading, Bavelier et al. (1997) found a large variability in individual patterns of activation across different individuals.
Other studies have found significant gender differences in the size of the brain areas associated with language – Harasty et al. (1997) found that women have proportionally larger Broca’s and Wernicke’s areas than men
C:This suggests that the size of these areas are related to the use of language i.e. there is generally a greater use of language amongst women – plasticity due to experience.
