Language dominance in neurologically normal and epilepsy subjects - A functional MRI study

Language dominance and factors that influence language lateralization were investigated in right-handed, neurologically normal subjects (n = 100) and right-handed epilepsy patients (n = 50) using functional MRI. Increases in blood oxygenation-dependent signal during a semantic language activation ta sk relative to a non-linguistic, auditory discrimination task provided an i ndex of language system lateralization, As expected, the majority of both g roups showed left hemisphere dominance, although a continuum of activation asymmetry was evident, with nearly all subjects showing some degree of righ t hemisphere activation. Using a categorical dominance classification, 94% of the normal subjects were considered left hemisphere dominant and 6% had bilateral, roughly symmetric language representation. None of the normal su bjects had rightward dominance, There was greater variability of language d ominance in the epilepsy group, with 78% showing left hemisphere dominance, 16% showing a symmetric pattern and 6% showing right hemisphere dominance, Atypical language dominance in the epilepsy group was associated with an e arlier age of brain injury and with weaker right hand dominance. Language l ateralization in the normal group was weakly related to age, but was not si gnificantly related to sex, education, task performance or familial left-ha ndedness.