The crucial role of posterior frontal regions in modality specific components of the spelling process.

Although it is commonly assumed that posterior temporo-parietal regions are the regions of the brain essential for accessing orthographic representations for written output, patients with lesions in these areas also have reading and/or naming impairments at least early after stroke onset. This observation raises the possibility that these regions are important for components of spelling that are not specific to written output. The goal of the present study was to identify any regions of the brain that, when damaged, result in selective impairment in accessing orthographic representations for written output. We studied 54 consecutive right-handed patients with acute, left hemisphere ischemic stroke, who were barely able to perform the motor aspects of writing with the right hand and had at least 10th grade education, on a battery of lexical tasks designed to identify impaired and spared cognitive processes underlying spelling and with advanced magnetic resonance imaging. Only five patients had pure agraphia, and had evidence of impaired access to lexical-orthographic representations for output; and all five had infarct or ischemia in Brodmann's area 44 and 45. Analysis of performance across tasks of three of these patients, whose performance has not been previously reported, provides evidence for additional impairment in converting graphemes to letter shapes or letter-specific motor programs. These three patients, unlike previously reported patients with lexical-orthographic impairment and compromised function in Brodmann's area 44 and 45, also had infarcts in Brodmann's area 6. On the basis of these cases, and those in the literature, we propose a network of brain regions involved in writing words, each with a separate function. This proposal emphasizes the role of the left posterior frontal regions in modality-specific output processes.