Cortical DC-potentials in identification of the language-dominant hemisphere: linguistical and clinical aspects

In order to find a non-invasive method for determining the hemispheric dominance for language, we studied cortical activation patterns during language processing by means of electrophysiological techniques: DC-potentials were recorded from frontal, central, temporal and parietal electrode positions in 28 right-handed normal subjects and in 16 patients with a history of transient loss of speech and known hemispheric dominance. Subjects were asked to find as many synonyms as possible within 6 seconds to either a concrete or an abstract noun. This task caused a highly significant left-hemispheric lateralization over frontal and central, but not over temporal and parietal cortical areas. Search for synonyms to abstract nouns yielded frontal left-hemispheric dominance in 93% of all normal subjects, search for synonyms to concrete nouns in 85%. Inter-electrode correlation coefficients were higher during processing of abstract word categories than during processing of concrete categories. In all patients, frontal and central lateralization corresponded to their hemispheric dominance as determined from clinical data. Advantages as well as inconveniences of this technique are discussed and compared to other invasive and noninvasive tools of assessing speech lateralization.