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  Aphasiology (Greek, ‘study of speech disorder’), in linguistics, is the study of language disorders which have been caused by brain damage. Injury can occur through serious accidents; via disease, such as tumours; or as the result of cerebro-vascular accident (stroke). As in many areas of science, the rationale behind aphasiology is that we can often gain valuable insights into the workings of a system when that system breaks down. It is hoped, then, that specific malfunctions in the speech of aphasic patients will shed light on the functioning of the unimpaired language system.

One of the earliest discoveries in aphasiology was reported by the French neurologist Paul Broca in 1861. Two of Broca\'s patients had severe language disorders (one of them was reduced to the two pronouncements tan and sacré nom de dieu). From a subsequent autopsy performed on these patients, it emerged that they had both suffered damage to a specific area in the front portion of the left hemisphere of the brain (later dubbed Broca\'s area). It has since been found that patients suffering from Broca\'s aphasia can generally understand what is said to them, but have considerable difficulty in producing speech. Sentences tend to be short and are produced intermittently, with long pauses in between. Broca\'s aphasia is also characterized by agrammatical sentences which arise from the omission of so-called function words, such as ‘the’, ‘of’ and ‘to’.

Since Broca\'s pioneering studies, research in aphasiology has implicated several other areas of the brain as potential speech centres. One of the most important, located in the posterior part of the left hemisphere, was named Wernicke\'s area after Carl Wernicke in 1872. Patients suffering from Wernicke\'s aphasia possess fluent speech with generally intact grammatical structure. There may, however, be problems in attaching affixes, such as ing, in the appropriate context (for example, ‘is louding’ instead of ‘is loud’). However, the most notable symptom of Wernicke\'s aphasia is a drastic reduction in the powers of speech comprehension.

A recurrent theme in aphasiology research has been the suggestion that damage to particular areas of the brain leads to specific language disorders. This finding would seem to suggest that certain language functions are highly localized. From the discussion of Broca\'s aphasia and Wernicke\'s aphasia above, for example, it might be tempting to conclude that Broca\'s area is crucial for the production of speech, whereas Wernicke\'s area controls the ability to process and understand speech. Although this localization hypothesis is still favoured by many researchers, others recommend caution since the effects of neurological damage, though seemingly highly localized, can in fact have unforeseen consequences in other areas. Most obviously, the immediate area leading to a brain lesion may be flooded with blood, while the area beyond the damaged section may be starved of blood. Thus, the normal functioning of otherwise unaffected regions can be seriously disrupted. Evidently, aphasiology can provide us with invaluable insights into the relationship between brain and language, but we should be aware that injured brains may not always be representative of normal ones. MS

See also neurolinguistics.Further reading R. Lesser, Linguistic Investigations of Aphasia.



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