PATTERNS OF LANGUAGE DOMINANCE IN FOCAL LEFT AND RIGHT-HEMISPHERE EPILEPSIES - RELATION TO MRI FINDINGS, EEG, SEX, AND AGE AT ONSET OF EPILEPSY

The present study evaluates results of language testing during intraca rotid amobarbital procedures in 167 patients with either left (LHE, n = 81) or right hemisphere epilepsies (RHE, n = 86). In both groups the re was a high rate of deviance from complete left hemisphere dominance of 24 and 31%, respectively. Whilst complete right hemisphere or inco mplete left hemisphere language dominance were the prominent atypical patterns in LHE, RHE was associated with either bilateral dominance or incomplete left dominance. In LHE, atypical language dominance was fr equently associated with an extratemporal localization of lesions or e pileptic foci. The age at onset of epilepsy and the degree of right he misphere language dominance correlated significantly in LHE but not in RHE. Finally, atypical dominance in LHE but not in RHE was associated with poorer language and nonlanguage functions, the latter being nega tively correlated with the degree of right hemisphere language dominan ce. Conclusions are: (1) The data contradict the assumption of equipot entiality and favor the supposition of a predetermined left hemisphere superiority in language processing. (2) Atypical language dominance i n LHE can largely be explained in terms of a plasticity dependent lang uage shift as a consequence of early left hemisphere epilepsies and le sions. (3) Atypical dominance patterns in RHE appear to reflect the pr evalence of genetically determined variants and the possibility of a l anguage transfer from the right to the left hemisphere. (C) 1997 Acade mic Press.