Speech mapping using depth electrodes: The "electric Wada".

OBJECTIVES: The Wada test is the gold standard for identification of the side of speech dominance but is associated with risk of angiography and requires patient cooperation. We report a method to verify speech laterality using implanted electrodes in patients undergoing stereo-encephalography (SEEG).

PATIENTS AND METHODS: Four pediatric patients with frontal lobe drug-resistant epilepsy underwent implantation of multiple SEEG electrodes using framed stereotaxy to identify the epileptogenic zone, including electrodes placed bilaterally into the pars opercularis of each inferior frontal gyrus from a superior parasagittal entry point. Biphasic stimulation at 50Hz, 0.3ms pulse width, up to 10mA was administered to distal contacts during a reading task.

RESULTS: Speech arrest upon stimulation was obtained when stimulating distal contacts in the inferior frontal gyrus on one side with no effect on the contralateral side, establishing language laterality in every patient. This information was used to plan subsequent surgical treatment. There were no adverse events of implantation or stimulation.

CONCLUSIONS: Brain mapping using SEEG electrodes is feasible and can be used to lateralize speech dominance. In cases of frontal lobe epilepsy in which electrodes will be implanted bilaterally for recording of ictal activity, this technique may make the Wada test unnecessary.