Objective: To investigate the relationship between language lateralization and handedness in patients with epilepsy and a left-sided seizure focus and in healthy control subjects.
Methods: We recruited a consecutive series of 74 patients and 70 control subjects. Functional MRI, using a noun-verb generation task, was performed to establish the language laterality index (LI). Handedness was quantified using the Edinburgh Handedness Inventory.
Results: Patients showed a shift toward atypical language lateralization (0.43 +/- 0.47; controls 0.57 +/- 034; p < or = 0.05) and left-handedness (55 +/- 57; controls 74 +/- 39; p < or = 0.05). The LI and handedness were correlated in patients (r = 0.54; F = 25.9; p < 0.001) but not in control subjects (r = 0.1; F = 0.64; NS). A combination of left-handedness and atypical LI was more frequent in patients (12%) than control subjects (0%; p < or = 0.05). Crossed hemispheric specialization (e.g., right-handedness associated with atypical LI) was equally frequent in patients (20%) and control subjects (16%; NS).
Conclusion: In epilepsy patients with a left-sided seizure focus, language lateralization is correlated to handedness. The increased frequency of left-handedness and associated atypical language lateralization is most likely related to the left-hemispheric seizure focus, influencing hemispheric specialization for both domains.