The anatomy of writing processes: Evidence from acquired dysgraphia in a shallow orthography language

The neural bases of spelling impairments are still uncertain, as only a paucity of single-case studies have been published so far on this topic. In this study we report the results of an investigation involving 35 left focal brain-damaged patients suffering from acquired surface, and phonological, dysgraphia. Patients were tested with four writing tasks, namely spelling of regular words, irregular words, loan words and nonwords. We used the subtraction technique and voxel-based lesion-symptom mapping (VLSM) procedure to highlight the anatomical correlates of functional damage along the lexical and sublexical routes of spelling. We found that surface dysgraphia is predominantly associated with left temporo-occipital lesions, along with lesions occurring in the left angular gyrus and the left supramarginal gyrus. Phonological dysgraphia follows from lesions in the left insular cortex, and a number of white matter tracts, such as the left external capsule, and the left superior longitudinal fasciculus. Results from VLSM analyses investigating spelling along the lexical/sublexical routes were consistent with those obtained using the subtraction condition. In brief, the results of this investigation indicate that different types of acquired dysgraphia result from damage to different cortical areas and subcortical pathways. Furthermore, data are consistent with dual-route models of spelling, and with a crucial role of subcortical white-matter pathways in spelling along the sublexical route.