Neuropsychological Disorders Of Writing

Having identified the major functional components of the normal writing process, we now turn our attention to clinical disorders of writing in patients with neurological damage. If we are correct in assuming that the various processing components of our cognitive model are subserved by dedicated neural systems, then damage to specific brain regions should be associated with distinct types of agraphia. Selective damage to a single processing component should result in a "pure" agraphia syndrome with a characteristic and predictable combination of impaired and preserved writing abilities. Specifically, the particular functions assigned to the damaged module should be disrupted, whereas those mediated by other modules should be relatively spared. Although pure cases fulfilling these criteria are encountered occasionally, in clinical practice writing disorders often display features consistent with simultaneous damage to several processing modules, resulting in mixed or multicomponent agraphia syndromes.

From a neuropsychological perspective, agraphia syndromes can be subdivided into central and peripheral types. In essence, this classification system is similar to the distinction between linguistic versus motor forms of agraphia introduced by previous investigators. Central agraphias reflect damage to the proposed linguistic spelling routes or the graphemic buffer. These syndromes are characterized by qualitatively similar spelling deficits across all possible modalities of output (i.e., writing, oral spelling, typing, and spelling with anagram letters). In contrast, in the peripheral agraphias the damage involves processing components located distal to the graphemic buffer (Fig. 2), and the impairment primarily affects the selection and production of letters in handwriting.

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