Cortical language lateralization in right handed normal subjects using functional magnetic resonance imaging

lIn 95% of right handed individuals the left hemisphere is; dominant for sp eech and language function. The evidence for this is accumulated primarily from clinical populations. We investigated cortical topography of language function and lateralization in a sample of the right handed population usin g functional magnetic resonance imaging and two lexical-semantic paradigms. Activated cortical language networks were assessed topographically and qua ntitatively by using a lateralization index. As a group, we observed left h emispheric language dominance. Individually, the lateralization index varie d continuously from left hemisphere dominant to bilateral representation. I n males, language primarily lateralized to left, and in females, approximat ely half had left lateralization and the other half had bilateral represent ation. Our data indicate that a previous view of female bilateral hemispher ic dominance for language (McGlone, 1980. Sex differences in human brain as ymmetry: a critical survey. Behav Brain Sci 3:215-263; Shaywitz et al., 199 5. Sex differences in the functional organization of the brain for language . Nature 373:607-609) simplifies the complexity of cortical language distri bution in this population. Analysis of the distribution of the lateralizati on index in our study allowed us to make this difference in females apparen t. (C) 2000 Elsevier Science B.V. All rights reserved.