Atypical language lateralization: an fMRI study in patients with cerebral lesions

Differences in the lateralization of language processes between healthy subjects and patients with neurological complaints other than epilepsy have been less documented than those between healthy subjects and epilepsy patients. Moreover, the contribution of factors such as the location and type of lesion in determining interhemispheric shift of language function is poorly understood. Sixty-seven patients who underwent presurgical evaluations at the Medical Imaging Center of the Imam Khomeini University Hospital, Tehran, and the same number of healthy controls, were recruited. The laterality index (LI) of language activation, calculated from two separate functional magnetic resonance imaging tasks, was compared between the patients and the age-/gender-/handedness-matched controls. Chi square testing showed that the percentages of subjects with "typical" and "atypical" language dominance in the patient group were significantly different from the percentages recorded in the matched healthy controls for both tasks (p<0.005). Lesion type, lesion location, lesion hemisphere, presenting symptom and patient gender had no statistically significant effect on the hemispheric LI (p>0.05). In a logistic regression model including all potential determinants of atypical LI, age emerged as the only independent predictor (p<0.05, odds ratio=0.9). Abnormal language lateralization is found in patients with a variety of cerebral lesions and with a diversity of clinical manifestations. In our selected population, symptom duration, lesion hemisphere and anatomical site of the lesion were not found to impact significantly on the development of an abnormal LI while patient age can independently predict the presence of an atypical LI.