Right unilateral jargonagraphia as a symptom of callosal disconnection

We report the case of a right-handed patient who exhibited right unilateral jargonagraphia after a traumatic callosal hemorrhage. The lesions involved the entire corpus callosum, except for the lower part of the genu and the splenium. The patient's right unilateral jargonagraphia was characterized by neologisms and perseveration in kanji and kana, and was more prominent in kana than kanji. The jargonagraphia was similar to that observed in crossed aphasia, except that agraphia occurred only with the right hand. The patient also showed right unilateral tactile anomia and right tactile alexia, along with right-ear extinction on a dichotic listening test for verbal stimuli, which suggested that language function was lateralized to the right hemisphere. Since this patient had learned to write with his right hand, kinesthetic images of characters were thought to be formed and stored dominantly in the left hemisphere. We suggest that the callosal lesions disturbed the interhemispheric transfer of information for the dual-route procedures for writing in the right hemisphere, allowing the kinesthetic images of characters stored in the left hemisphere to be processed freely, resulting in the right unilateral jargonagraphia. At least two factors seem to explain that kana was more defective than kanji. First, writing in kana, which is assumed to be processed mainly via a sub-word phoneme to grapheme conversion route, might depend more strongly on lateralized linguistic processing than writing in kanji. Second, kanji, which represent meaning as well as phonology, with much more complicated graphic patterns than kana, are assumed to be processed in both hemispheres.