Central and peripheral components of writing critically depend on a defined area of the dominant superior parietal gyrus.

Classical neuropsychological models of writing separate central (linguistic) processes common to oral spelling, writing and typing from peripheral (motor) processes that are modality specific Damage to the left superior parietal gyms, an area of the cortex Involved in peripheral processes specific to handwriting, should generate distorted graphemes but not misspelled words, while damage to other areas of the cortex like the frontal lobe should produce alterations in written and oral spelling without distorted graphemes We describe the clinical and neuropsychological features of a patient with combined agraphia for handwriting and typewriting bearing a small glioblastoma in the left parietal lobe. His agraphia resolved after antiedema therapy and we tested by bipolar cortical stimulation his handwriting abilities during an awake neurosurgical procedure We found that we could reversibly re-induce the same defects of writing by stimulating during surgery a limited area of the superior parietal gyms in the same patient and in an independent patient that was never agraphic before the operation In those patients stimulation caused spelling errors, poorly formed letters and in some cases a complete cessation of writing with minimal or no effects on oral spelling Our results suggest that stimulating a specific area in the superior parietal gyms we can generate different patterns of agraphia Moreover, our findings also suggest that some of the central processes specific for typing and handwriting converge with motor processes at least in the limited portion of the superior parietal gyms we mapped in our patients