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Localisation of function in the Brain. What is localisation ?.
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Whatislocalisation? • The brain exhibits "localization of function." This means that different parts of the brain carry out different functions (e.g., vision, control of voluntary movement, understanding speech, etc.) and, conversely, that not all parts of the brain do the same thing. This may seem obvious, but other organs, such as the liver, do not exhibit localization of function; one part of the liver does the same thing as another part six inches away.
It all started…….. • The process of identifying the parts of the brain that are involved in language began in 1861, when Paul Broca, a French neurosurgeon, examined the brain of a recently deceased patient who had had an unusual disorder. Though he had been able to understand spoken language and did not have any motor impairments of the mouth or tongue that might have affected his ability to speak, he could neither speak a complete sentence nor express his thoughts in writing. The only articulate sound he could make was the syllable “tan”, which had come to be used as his name.
Autopsy…. • When Broca autopsied Tan’s brain, he found a sizable lesion in the left inferior frontal cortex. Subsequently, Broca studied eight other patients, all of whom had similar language deficits along with lesions in their left frontal hemisphere. This led him to make his famous statement that “we speak with the left hemisphere” and to identify, for the first time, the existence of a “language centre” in the posterior portion of the frontal lobe of this hemisphere. Now known as Broca’s area, this was in fact the first area of the brain to be associated with a specific function—in this case, language.
Wernickes area • Ten years later, Carl Wernicke, a German neurologist, discovered another part of the brain, this one involved in understanding language, in the posterior portion of the left temporal lobe. People who had a lesion at this location could speak, but their speech was often incoherent and made no sense.
Language loop • This language loop is found in the left hemisphere in about 90% of right-handed persons and 70% of left-handed persons, language being one of the functions that is performed asymmetrically in the brain. Surprisingly, this loop is also found at the same location in deaf persons who use sign language. This loop would therefore not appear to be specific to heard or spoken language, but rather to be more broadly associated with whatever the individual’s primary language modality happens to be.
Deafness… • The loop can help therefore to explain, why and how deaf people understand what is being communicated to them and how they come to produce a response.
Phineas gage…. • Phineas Gage- a case that also shows localization of function in the brain
Listen to Phineas story. • Phineas was an American railroad construction foreman now remembered for his incredible survival of an accident in which a large iron rod was driven completely through his head, destroying much of his brain's left frontal lobe, and for that injury's reported effects on his personality and behavior—effects so profound that friends saw him as "no longer Gage.
The Doctor…. • I first noticed the wound upon the head before I alighted from my carriage, the pulsations of the brain being very distinct. Mr. Gage, during the time I was examining this wound, was relating the manner in which he was injured to the bystanders. I did not believe Mr. Gage's statement at that time, but thought he was deceived. Mr. Gage persisted in saying that the bar went through his head....Mr. G. got up and vomited; the effort of vomiting pressed out about half a teacupful of the brain, which fell upon the floor
Waiting…. • Despite Harlow's skillful care,[n 8] Gage's recuperation was long and difficult. Pressure on the brain[n 9] left him semi-comatose from September 23 to October 3, "seldom speaking unless spoken to, and then answering only in monosyllables. The friends and attendants are in hourly expectancy of his death, and have his coffin and clothes in readiness."
Recovery… • But on October 7 Gage "succeeded in raising himself up, and took one step to his chair." One month later he was walking "up and down stairs, and about the house, into the piazza," and while Harlow was absent for a week, Gage was "in the street every day except Sunday,"
Task- • Produce a leaflet (to be used as a revision aid) on Localization of function. What is it? When did we first realize it? Broca and Wernickes aphasia, Tan, Phineas……… • Include pictures and diagrams.
