Right hemisphere language mapping in patients with bilateral language

The configuration of language cortex in the dominant left hemisphere has been well described in the literature. However, language representation in the right hemisphere, particularly in patients with some degree of bilateral language, remains unclear. Herein, we report six patients who underwent electrocortical stimulation (ECS) for language mapping following implantation of a right subdural electrode array (SEA).

The medical records of six bilateral language patients with right SEA implantation at the Minnesota Epilepsy Group between January 1996 and July 2004 were retrospectively reviewed. Language lateralization was based on the results of the intracarotid amobarbital procedure performed preoperatively. Anatomical localization of the SEA for each patient was verified using colored photographs of the cortical surface before and after SEA placement and by review of MRI scans taken with the SEA in place. Frontal and temporal language areas were identified by errors in any language modality including automatic speech, reading, naming, repetition, and comprehension during ECS.

Language maps revealed the presence of frontal and/or temporal language areas analogous to the classic essential language areas of the dominant left hemisphere in four of six patients. One patient had a widespread distribution of single-language-error sites over the right temporal lobe. One patient had a silent language map.

Our results identified the presence of language cortex in the right hemisphere in five of six patients classified with bilateral language based on intracarotid amobarbital procedure. These areas are assumed to be accessory language zones in relation to the left hemisphere. Further exploratory studies are needed to evaluate their clinical significance.