A delay or abnormality associated with any function of language and communication.
In adults, much of what is known about the organization of language functions in the brain has come from the study of patients with focal brain lesions. For example, it is well known that a left-hemisphere injury to the brain is more likely to cause language disturbance—aphasia—than a right hemisphere injury, especially, but not exclusively, in right-handed persons. Certain areas in the adult left hemisphere—Broca's area in the posterior frontal lobe, and Wernicke's area in the temporal lobe, have been identified as centrally involved in language functions. However, researchers in the field of adult aphasia are divided over the exact function of these two areas of the brain in language processing and production. Damage to Broca's area results in marked problems with language fluency, including shortened sentences, impaired flow of speech, poor control of rhythm and intonation (prosody); and use of a telegraphic style, with missing inflections and function words. In contrast, the speech of Wernicke's aphasia is fluent and often rapid, but with relatively empty content and many invented words (neologisms) and word substitutions. Although it was initially believed that the two areas were responsible for output (Broca's) versus input (Wernicke's), research does not confirm such a simple split.
The study of infants and young children diagnosed with focal brain lesions before they acquire language provided valuable information to neuro-scientists who want to know how “plastic” the developing brain is with respect to language functions. For instance, is the left hemisphere uniquely equipped for language, or could the right hemisphere do as well? What if Broca's or Wernicke's areas were damaged before language was acquired? Left-brain damage has been shown to cause greater disruption to language than right-sided damage even in the youngest subjects. Children known to be using only their right hemisphere for language (i.e., after removal of the left hemisphere due to congenital abnormalities) demonstrated subtle syntactic deficits on careful linguistic testing, but the deficits failed to appear in ordinary conversational analysis.
Advanced imaging technologies such as CT scans and magnetic resonance imaging (MRI) have allowed researchers to look prospectively at the language development of children with focal, defined lesions specifically in the traditional language areas. Brain imaging, for example, has helped to provide evidence of neuro-cognitive dysfunction underlying non-lesion-specific brain disorders such as Ashberger's syndrome. Surprising concordance has been noted in the results of studies, including identifying initial, though variable, delays in the onset of lexical, syntactic, and morphological development followed by remarkably similar progress after about age two to three years. Lasting deficits have not been noticed in these children and no dramatic effects of laterality, with lesions on either side of the brain producing virtually the same effects. Results of the studies are limited by not following the children longitudinally until school age. However, the findings suggest remarkable plasticity and robustness of language in spite of brain lesions that would devastate an adult's system.
Children's speech and language development follows a typical pattern, and parents, teachers, and physicians who are aware of the general pattern may notice certain signs and symptoms in a child consistent with language delays or other speech and language problems. Signs and symptoms may include not speaking at all in the early stages of infancy, not speaking at an age-appropriate level, not expressing ideas clearly, difficulties with both spoken and written words, difficulty learning new words, and misunderstanding spoken questions or directions. Speech language pathologists evaluate spoken language, both speaking and listening abilities, and written language for children whose parents or teachers observed them to be having difficulties of some kind. Parents, educators, and speech pathologists form a diagnostic team and evaluation may include observing the child at home and at pre/school or school, gathing information about literacy in the home, assessing the child's ability to understand verbal and written directions, assessing attention levels, determining if the child holds a book and turns pages correctly, and observing the child's writing or pretend-writing and his recognition of letters and numbers. Articulation may be evaluated to see if it supports written language skills.
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