Cerebral and callosal organisation in a right hemisphere dominant "split brain" patient.

Patients described in previous reports who have undergone corpus callostomy for control of seizures have been left hemisphere dominant for language. To determine the hemispheric localisation (and possible coexistence) of language and traditional right hemisphere skills in reversed dominance, the first right hemisphere dominant corpus callostomy patient was studied. Localisation of callosal functions was also investigated, as MRI showed 1.5 cm of spared callosal body. The patient, KO, a 15 year old girl with familial left handedness, underwent two stage callosotomy in 1988. Lateralised visually presented stimuli requiring same or different comparisons between visual fields showed chance performance. Oral naming and reading showed better performance by the right hemisphere than the left, whereas both hemispheres were proficient in auditory comprehension. Active voice syntax was above chance only in the right hemisphere. Face recognition was significantly better in the right hemisphere than in the left. Tasks requiring tactile comparisons between hands showed above chance performance except in the instance in which the non-dominant right hand was stimulated first in a point localisation task between hands. This case showed hemispheric coexistence of language and traditional right hemispheric skills in a corpus callosotomy patient with reversed language dominance. Tactile transfer was localised to the mid-posterior callosal body.