Manipulo-spatial processing of ideographic characters in left-handers: observation in fMRI

It has been suggested that left-handers have a cerebral ambilaterality for language representation. Specifically, the use of the right hand for writing may have a specific effect on the cerebral organization in left-handers. In an investigation of the relationship between motor and visual language procedures, functional magnetic resonance imaging at three tesla was conducted during stroke counting of kanji (Japanese ideographic characters) in six left-handers who usually write with their right hand. Two types of stimulus presentation, phonography-displayed and kanji-displayed, were employed to examine the different neural pathways used for processing kanji. Each stimulus presentation involved two motor conditions: one allowed finger movements for tracing the characters, while the other disallowed finger movements. The tasks induced activation in the primary motor area, the premotor area, the supplementary motor area, and the anterior cingulate gyrus as well as the parietal and occipital lobes (Brodmann's area 7/39/19). The activated areas in both the movement-allowed and movement-disallowed conditions were almost identical except for the primary motor area. These results clearly contrasted with those of a previous study of right-handers which showed that right-handed volunteers demonstrated decreased activation in the premotor area and the dorsal pathway during the movement-allowed condition. This discrepancy may be attributable to a difference in cerebral organization for language processing. Specifically, in left-handers, the visuospatial procedure for kanji and the motor procedure for tracing the kanji may be ambilaterally distributed in both hemispheres, whereas in right-handers these procedures may be predominantly lateralized in the left hemisphere.