Language dominance in neurologically normal and epilepsy subjects

TLDR

The study examined language dominance and its influencing factors in 100 right‑handed healthy controls and 50 right‑handed epilepsy patients via fMRI. Language lateralization was indexed by comparing BOLD signal increases during a semantic task versus a non‑linguistic auditory task. Most participants showed left‑hemisphere dominance (94 % of controls, 78 % of epilepsy patients), with a minority exhibiting bilateral or right‑hemisphere patterns; atypical dominance in epilepsy correlated with earlier brain injury and weaker right‑hand dominance, while in controls dominance was only weakly linked to age and unrelated to sex, education, task performance, or family left‑handedness.

Abstract

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 task relative to a non-linguistic, auditory discrimination task provided an index of language system lateralization. As expected, the majority of both groups showed left hemisphere dominance, although a continuum of activation asymmetry was evident, with nearly all subjects showing some degree of right 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 subjects had rightward dominance. There was greater variability of language dominance 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 earlier age of brain injury and with weaker right hand dominance. Language lateralization in the normal group was weakly related to age, but was not significantly related to sex, education, task performance or familial left-handedness.