Quantitative and qualitative evaluation of patterns of cerebral language dominance. An amobarbital study

As a part of presurgical evaluation, 173 patients received bilateral intracarotid amobarbital tests for determination of cerebral language dominance. Language testing during intracarotid amobarbital procedures (IAP) consisted of the following tasks: automatic speech, sentence comprehension, body commands, naming, repetition, reading, and spontaneous speech. Patterns of cerebral language dominance were evaluated and discussed on five levels of analysis: (1) quantification of language dominance on the basis of a lateralization index derived from the total language scores in each IAP; (2) determination of five dominance subpatterns (left or right dominant, strongly bilateral, and incomplete left or right dominant) according to quantification performed on level (1) and clinical judgement; (3) qualitative differentiation of three kinds of bilaterality (positive, negative, and general) according to total language performance in left and right IAP; (4) analysis of grouped linguistic subfunctions extracted from performance in specific IAP subtests; (5) extraordinary individual case histories. The distribution of lateralization indices revealed only partially continuous degrees of lateralization, especially between the left-dominant and bilateral subgroups. As for the clinically oriented classification, incomplete left dominance is frequent (16.2%), while incomplete right dominance does not occur at all. Atypical dominance patterns are mostly correlated to bilateral and/or extratemporal foci. Concerning grouped subfunctions, a rotated factor matrix statistic yields an analysis of clusters of IAP subtests, where functions involving expressive language capacities are separated from those that are purely receptive. Further analyses of bilaterality subpatterns suggest that there are mainly four bilaterality phenomena, namely interhemispheric dissociation, double representation, unilateral representation of subfunctions, and partial representation of subfunctions in either hemisphere. Application of these differentiations to individual cases yields additional evidence that can be used in patient selection for operation in order to avoid postoperative neuropsychological deficits, especially in candidates for extratemporal surgery. In conclusion, a multilevel analysis of IAP language data is recommended since it permits a detailed account of varieties of language dominance patterns and contributes to more adequate presurgical decision-making in planned operations in cognitively relevant brain areas.