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Impairment in the use of spoken or written language caused by injury to the brain which cannot be accounted for by paralysis or incoordination of the articulatory organs, impairment of hearing or vision, impaired level of consciousness, or impaired motivation to communicate. The language zone in the brain includes the portion of the frontal, temporal, and parietal lobes surrounding the sylvian fissure and structures deep to these areas. In right-handed persons, with few exceptions, only injury in the left cerebral hemisphere produces aphasia. Lateralization of language function is variable in left-handers, and they are at greater risk for becoming aphasic from a lesion in either hemisphere. See Hemispheric laterality
Distinctive recurring patterns of deficit are associated with particular lesion sites within the language zone. These patterns may entail selective impairment of articulation, ability to retrieve concept names, or syntactic organization. Other dissociations affect principally the auditory comprehension of speech, the repetition of speech, or the recognition of written words. The erroneous production of unintended words in speech (paraphasia), oral reading (paralexia), or writing (paragraphia) is a feature of some forms of aphasia.
Mixed forms of aphasia, caused by multiple lesions or lesions spanning anterior and posterior portions of the speech zone, are quite common, and massive destruction of the entire language area results in a global aphasia. Further, individual variations in behavioral manifestations of similar lesions have set limits on the strict assignment of function to structures within the language area.
Preadolescent children suffering aphasia after unilateral injury usually recover rapidly, presumably by virtue of the capacity of the right cerebral hemisphere early in life to acquire the language functions originally mediated by the left hemisphere. Capacity for recovery of function decreases during later adolescence and young adulthood.
Complete recovery in adults after a severe injury is much less common, and severe aphasia may persist unchanged for the duration of the person's life. Many patients are aided by remedial language training, while others continue severely impaired. See Memory
a speech disturbance consisting in the loss of the ability to use words and phrases as the means of expressing thought; it is caused by lesions in certain zones of the cerebral cortex. Expressive speech (that is, the utterance of words and phrases) may also be impaired as a result of an affection of the executive speech apparatus (tongue, lips, vocal cords). However, such impairments are not included in the concept of aphasia, since in aphasia the patient is able to utter all sounds, but is incapable of speaking. The impairment of impressive speech (that is, understanding speech that is heard) in aphasia differs from that in deafness, since all sounds are perceived, but words sound like unknown signals. Aphasia occurs when there is an affection of the cortex of the left cerebral hemisphere in right-handed persons; and of the right hemisphere in left-handed ones. Motor, sensory, amnesic, conduction, and total aphasias are differentiated.
Motor aphasia is principally caused by an affection of the posterior portions of the inferior frontal gyrus and is manifested by the impairment of expressive speech (speech is either completely impossible or difficult); the grammatical structure of speech is disrupted; the patient transposes or substitutes letters in words. Voluntary speech (narration, conversational speech) suffers more than repetition or automatic speech. This form of aphasia is combined with the impairment of writing—agraphia.
Sensory aphasia occurs when focuses of disease are present in the surface zones of the temporal lobe of the brain. It is manifested by the impairment of impressive speech to the point of complete incomprehension and also the impairment of expressive speech as a result of the absence of auditory control over the words uttered. When paraphasic errors occur, one word is replaced by another that is similar in sound but different in meaning. In severe cases speech becomes completely unintelligible. This form is often combined with the impairment of reading (alexia).
Amnesic aphasia consists in forgetting the names of objects and attempting to substitute descriptions of the objects for their names. It is often combined with sensory aphasia.
The other forms of aphasia, total and conduction, are more rarely observed. Total aphasia is manifested by the impairment of expressive, as well as impressive, speech. Conduction aphasia occurs when there are large focuses of disease in the white matter of the hemispheres of the cerebral cortex. Aphasias have been described that are caused by disease not only of the cortical but also of the deeper formations, which testifies to the complex architecture of the functional system that provides for speech.
Causes of aphasia are vascular diseases of the brain, en-cephalitides, traumas, and brain tumors. Treatment is directed at the illness causing the aphasia. Speech processes impaired in aphasia may be restored as a result of prolonged training based on the fact that the performance of acts of speech, writing, and reading can be reconstructed and that these acts include the processes of visual and kinesthetic analysis which are supported by the remaining sections of the cortex.
When aphasia occurs in childhood, it disrupts the course of the child’s general development. When sensory aphasia appears between the ages of five and seven years, it most often leads to the gradual disappearance of speech. Restorative work in this form of aphasia is extremely complicated. The child usually does not achieve normal speech development. Other forms of aphasia in children have a more favorable prognosis. Children suffering from aphasia are trained together with alalia patients. Systematic drill in speech and writing are very important.
REFERENCESLebedinskii, M. S. Afazii, agnozii, apraksii.Kharkov, 1941.
Filimonov, I. N. “Arkhitektonika i lokalizatsiia funktsii v kore bol’shogo mozga.” Mnogotomnoe rukovodstvopo nevrologii, vol. 1, book 2. Edited by N. I. Grashchenkov. Moscow, 1957. Page 147.
Tonkonogii, I. M. Insul’t i afaziia. Leningrad, 1968. (Bibliography pp. 262–66.)
Nielsen, J. M. “Agnosias, apraxias, speech and aphasia.” In Clinical Neurology, vol. 1. Edited by A. B. Baker. New York, 1962. Page 433.
A. M. VEIN