Abstract
Nine patients with lesions in the territory of the anterior cerebral artery (ACA) and 18 patients with other cerebral lesions were examined. All of the patients were usually writing with their right hands. They were requested to write replies to verbal questions, to take dictation or to copy with their left hand and to perform bimanual coordination tasks. Four patients out of 9 with ACA lesions presented pathologic left-handed mirror writing and mirror movements during bimanual coordination. None was accompanied by left-handed apraxia or agraphia, and one patient presented a grasping reflex in his left hand. Copying characters was done without difficulty with either hand without evidence of mirroring. Their corresponding lesions on CT scan involved the right supplementary motor are a and partially the anterior cingulate gyrus. Left-handed mirror writing ceased within several months in 3 patients, but in one patient whose CT lesion contained the entire right 6 Brodmann's area it continued for more than two years. In contrast, only one patient out of 18 who had a single cerebral lesion other than ACA territory showed left-handed mirror writing, and the symptomatology of his mirror writing presented no difference from that of the ACA lesions. Five patients with ACA lesions didn't present any mirror writing. Four of these patients had left-sided lesions and one was a right-sided lesion containing corpus callosum.
When the right supplementary motor area is destroyed and if a motor program such as writing or praxis to verbal commands that is organized predominantly by the left hemisphere is executed by the right primary motor area without non-mirror transformation, then mirror movements of the left hand will occur. Similarly in bimanual coordination tasks, the left hand will behave in a mirror fashion to the right because the right primary motor area receives only untransformed motor programs originating from the intact left supplementary motor area.
