Lexical agraphia. Further support for the two-system hypothesis of linguistic agraphia.

Eight patients with acquired agraphia were studied using the same writing tests and were compared with normal and brain-damaged controls. Four patients fulfilled the criteria for lexical agraphia and on CT scan had lesions of the posterior angular gyrus that spared the supramarginal gyrus. The other 4 fulfilled the criteria for phonological agraphia. They had lesions on CT scan that were similar to those found in previously described patients with phonological agraphia. Their lesions involved the supramarginal gyrus or insula deep to it and spared the angular gyrus. These studies support the hypothesis that there are two dissociable spelling systems and that these spelling systems are disrupted by focal lesions in separate but distinct brain regions. Further studies investigated the relationships between phonological agraphia and phonological dyslexia (alexia), and lexical agraphia and surface dyslexia (lexical alexia). The data support the hypothesis that individual systems subserve the four processes of phonological spelling, phonological reading, lexical spelling and lexical reading.