Language and the brain
Many people assume the physical basis of language lies in the lips, the tongue, or the ear. But deaf and mute people can also possess language fully. People who have no capacity to use their vocal cords may still be able to comprehend language and use its written forms. And human sign language, which is based on visible gesture rather than the creation of sound waves, is an infinitely creative system just like spoken forms of language. But the basis of sign language is not in the hand, just as spoken language is not based in the lips or tongue. There are many examples of aphasics who lose both the ability to write as well as to express themselves using sign-language, yet they never lose manual dexterity in other tasks, such as sipping with a straw or tying their shoes. Language is brain stuff--not tongue, lip, ear, or hand stuff. The language organ is the mind. More specifically, the language faculty seems to be located in certain areas of the left hemispheric cortex in most healthy adults. A special branch of linguistics, New medical imaging techniques such as PET and fMRI have allowed researchers to generate pictures showing which areas of a living brain are active at a given time. In the past, research was primarily based on observations of loss of ability resulting from damage to thecerebral cortex. Indeed, medical imaging has represented a radical step forward for research on speech processing. Since then, a whole series of relatively large areas of the brain have been found to be involved in speech processing. In more recent research, subcortical regions (those lying below the cerebral cortex such as the putamen and the caudate nucleus) as well as the pre-motor areas (BA 6) have received increased attention. It is now generally assumed that the following structures of the cerebral cortex near the primary and secondary auditory cortexes play a fundamental role in speech processing: * Superior temporal gyrus (STG): morphosyntactic processing (anterior section), integration of syntactic and semantic information (posterior section) * Inferior frontal gyrus (IFG, Brodmann area (BA) 45/47): syntactic processing, working memory * Inferior frontal gyrus (IFG, BA 44): syntactic processing, working memory * Middle temporal gyrus (MTG): lexical semantic processing The left hemisphere is usually dominant in right-handed people, although bilateral activations are not uncommon in the area of syntactic processing. It is now accepted that the right hemisphere plays an important role in the processing of suprasegmental acoustic features like prosody. Most areas of speech processing develop in the second year of life in the dominant half (hemisphere) of the brain, which often (though not necessarily) corresponds to the opposite of the dominant hand. 98 percent of right-handed people are left-hemisphere dominant, and the majority of left-handed people as well. What can language disorders tell us about the brain's language areas? Tourette's syndrome, which produces random and involuntary emotive reflex responses, including vocalizations This type of disorder, which often affects language use, is caused by a disfunction in the subcortex. There is no filter which prevents the slightest stimulus from producing a vocal response, sometimes of an inappropriate manner using abusive language or expletives. These words are involuntary and often the affected individual is not even aware of uttering them (like "um" in many individuals) and only realizes it when video is played back. This syndrome is not so much a language disorder per se as a disorder of the filters on the adult emotional reflex system--a kind of expletive hiccup. True language is housed in the cortex of the left hemisphere, not in the subcortical area that controls involuntary responses. Certain types of brain damage can affect language production without actually eliminating language from the brain. A stroke that...
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