Aphasic Agraphia

This is part of aphasia, whose type and severity it reflects. Therefore, screening for agraphia may be used in testing for aphasia. Lesions are located in the classical language zones (i.e., in the distribution of the middle cerebral artery; Figure 2).

Neurolinguistically, three types may be defined. Lexical agraphia consists of a disability to convert phonemes to graphemes, especially with irregular spelling, resulting in phonetic writing without lexical control. Lesion sites are the posterior superior parietal lobule and the angular gyrus. Phonologic agraphia consists of holistic writing of words with occasional failure to produce entire words that cannot be written in a letter-by-letter fashion. The patient fails in dictated pronounceable nonsense words while succeeding in well-known imageable words. Lesions are in the

B)

phonology

lexicon (semantics)

C)

syntax

double route

>

phoneme-to-grapheme conversion graphematic system

orthographic system

motor letter engram ["alphabet"]

motor word engram ["word pictures"]

motor letter engram ["alphabet"]

motor word engram ["word pictures"]

orthographic buffer allographic buffer

graphic motor program [(hand)writing]

Figure 2. Proposed neurolinguistic model of writing. The letters and numbers indicate the presumed sites of disruption.

anterior inferior supramarginal gyrus or the adjoining insula. Patients with semantic agraphia may successfully write real and nonsense words to dictation but have difficulties in written confrontation naming or description.

In analogy to deep and surface alexia, deep and surface agraphia have been distinguished. Deep agraphia is characterized by semantic paragraphias (e.g., airplane for propeller; Roeltgen, 1997), whereas in surface agraphia mostly literal paragraphias are produced (e.g., propettle for propeller). In languages with irregular orthography such as English, surface agraphia seems to be more frequent than in languages with regular orthography.

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