Abstracts

Rationale: Dual sided subdural electrodes are used in the localization and lateralization of seizure onset zones when the area of interest is within the inter-hemispheric fissure. They allow independent sampling of cortical signals from areas of both hemispheres with a single array of electrodes based on the assumption that each electrode only records from the hemisphere it faces, with no signal contamination from the opposite hemisphere. We designed the current study to test the validity of this assumption. Methods: We recorded with dual-sided strip and grid electrodes in two patients with non-occipital epilepsy during two visual stimulation tasks in which subjects were presented with visual stimuli in the ipsilateral or contralateral hemifelds. Electrophysiological signals were recorded from peri-calcarine visual areas on each side of the inter-hemispheric fissure.Results: Our findings show substantial contamination of recordings from the opposite hemisphere in both patients. Conclusions: We suggest that the current dual sided electrodes should not be used for lateralization of the origin of epileptic activity or evoked responses.