Language

A disturbance of language function is an intrinsic part of early AD and shows a steady progression in the time course of the dementia. At the early stages, the main feature in everyday language is anomia, accompanied by impoverished and circumlocutious language. As the dementia progresses, problems with comprehension appear to be more pronounced and the content of language becomes more vague, with syntactical and paraphasic errors. At the end stages, language is reduced to a few phases or even muteness. The following are the stages in the breakdown of language functioning:

Early AD

Word-finding difficulties Naming impairment Circumlocutory discourse Some problems with semantics Moderate AD

Impaired comprehension, particularly with complex material Simplified syntax

Content vague and sometime meaningless Paraphasias Verbal perseveration Severe dementia

Meaningless repetition of words Repetition of nonsense words Mutism

Systematic studies of language function in AD have focused on the different components and suggest a general pattern of disorder. In relation to phonetic or phonemic processing, the processing and production of the sound characteristics, there is relative preservation. Until the advanced stages, phonetic articulation of word and sentence systems is largely intact. To a certain extent this is true for syntactic processing, in the sense that simpler syntactic constructions appear normal. Nevertheless, syntactic simplification in written language has been noted as an early indication of AD. Phonology and syntax contrast markedly with word retrieval impairment, which is manifest in everyday language as an impoverishment of vocabulary associated with difficulties in finding the right words. Nouns tend to be more affected than adjectives, with verbs the least affected. Formal analysis of this impairment has focused on confrontation naming for objects and word fluency. The naming impairment may reflect in part a perceptual difficulty since it is exacerbated if the stimulus is a photograph or line drawing rather than an actual object. Analysis of the errors in naming suggests that they are also semantic in nature, with a breakdown in semantic memory in part underlying the language impairment. Word fluency impairment likewise may reflect a combination of word retrieval, semantic memory, and executive function impairment. The nature of the semantic impairment was discussed previously. Allied to this is a deficit in comprehension of both written and aurally presented material.

The language impairment in AD fits none of the main categories of aphasia, but comparison studies indicate that the closest similarity is with forms of aphasia with more posterior lesions within the neuronal language system (e.g., transcortical sensory dys-phasia). This is consistent with the neuropathology of AD, in which the main region of early cortical damage resides in the parietal and temporal lobes.

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