Language lateralization in healthy right-handers

Our knowledge about the variability of cerebral language lateralization is derived from studies of patients: with brain lesions and thus possible seco ndary reorganization of cerebral functions. In healthy right-handed subject s 'atypical', i.e, right hemisphere language dominance, has generally been assumed to be exceedingly rare. To test this assumption we measured languag e lateralization in 188 healthy subjects with moderate and strong right-han dedness (59% females) by a new non-invasive, quantitative technique previou sly validated by direct comparison with the intracarotid amobarbital proced ure, During a word generation task the averaged hemispheric perfusion diffe rences within the territories of the middle cerebral arteries were determin ed. (i) The natural distribution of language lateralization was found to oc cur along a bimodal continuum. (ii) Lateralization was equivalent in men an d women,. (iii) Right hemisphere dominance was found in 7.5% of subjects, T hese findings indicate that atypical language dominance in healthy right-ha nded subjects of either sex is considerably more common than previously sus pected.