LANGUAGE-RELATED HEMISPHERIC-ASYMMETRY IN HEALTHY-SUBJECTS AND PATIENTS WITH TEMPORAL-LOBE EPILEPSY AS STUDIED BY EVENT-RELATED BRAIN POTENTIALS AND INTRACAROTID AMOBARBITAL TEST

There are current attempts to replace the WADA test for pre-surgical e valuation of hemispheric language capabilities by one of the methods o f functional brain imaging. Recent PET and fMRI studies using verbal c ognitive tasks like verb generation, semantic monitoring or semantic ( 'deep') encoding of words showed asymmetries of activation in the fron to-lateral cortex. In a previous ERP study subjects were required to i ndicate whether pronounceable non-words and abstract geometric figures were presented for the first time ('new item') or whether they had be en shown before ('old item'). Group analyses of this study show ed sig nificant material-specific hemispheric asymmetries with ERPs being mor e negative-going in recordings of the posterior part of the left hemis phere with verbal material (CP5/6) but more negative-going in recordin gs of the right hemisphere with the spatial material (P7/8). The aim o f the present study was to test statistically ERP lateralization effec ts in individual healthy subjects as well as WADA-tested patients suff ering from seizures of the mesio-temporal lobe (MTL). In all subjects ERP lateralization with verbal material was tested in the electrode pa ir CP5/6, and ERP lateralization with figures in the electrode pair P7 /8. Statistical analyses of single trials showed that in 20 out of 24 subjects ERPs with verbal material started to be more negative-going i n CP5 as compared to CP6 in the period between 100 and 200 ms after st imulus onset or the subsequent time epoch (200-300 ms). In one subject not CP5/6 but the closely adjacent electrode pair P7/P8 showed this v erbal material-related hemispheric effect. In patients language domina nce as indicated by ERPs was not always consistent with the data of th e WADA test. In one patient with left MTL seizures ERPs with verbal ma terial and figures were found to be significantly lateralized to the r ight hemisphere although the WADA test assigned this patient to have a language-dominant left hemisphere. (C) 1998 Elsevier Science Ireland Ltd.