Left superior parietal cortex involvement in writing: integrating fMRI with lesion evidence

Writing is a uniquely human skill that we utilize nearly everyday. Lesion s tudies in patients with Gerstmann's syndrome have pointed to the parietal c ortex as being critical for writing. Very little information is, however, a vailable about the precise anatomical location of brain regions subserving writing in normal healthy individuals. In this study, we used functional ma gnetic resonance imaging (fMRI) to investigate parietal lobe function durin g writing to dictation. Significant clusters of activation were observed in left superior parietal. lobe (SPL) and the dorsal aspects of the inferior parietal cortex (IPC) bordering the SPL. Localized clusters of activation w ere also observed in the left premotor cortex, sensorimotor cortex and supp lementary motor area. No activation cluster was observed in the right hemis phere. These results clearly indicate that writing appears to be primarily organized in the language-dominant hemisphere. Further analysis revealed th at within the parietal cortex, activation was significantly greater in the left SPL, compared to left IPC. Together with lesion studies, findings from the present study provide further evidence for the essential role of the l eft SPL in writing. Deficits to the precise left hemisphere parietal cortex regions identified in the present study may specifically underlie disorder s of writing observed in Gerstmann's syndrome and apractic agraphia. (C) 20 01 Elsevier Science BY All rights reserved.