Abstracts

Rationale: Atypical language dominance is frequently identified in patients with focal epilepsy; the effect of seizure focus site within the left hemisphere is not well characterized. We aimed to examine the effect of seizure focus on the expression of regional language laterality by comparing patients with frontal and temporal seizure foci. We further compared the effect of neocortical versus mesial seizure focus in those patients with a temporal focus. Methods: We studied 90 patients (50 males; mean age 23.3 12.9 years) with left hemisphere focal epilepsy (mean age of onset 11.7 8.3 years). 18 patients had a frontal lobe focus, 72 temporal lobe focus (43 mesial; 29 neocortical). Subjects performed an auditory word definition language paradigm using 3T BOLD EPI fMRI. Data was analyzed in SPM2 using a region of interest (ROI) approach. Regional laterality indices (LI) for inferior frontal gyrus (IFG), and Wernicke s area (WA) were calculated using LI toolbox bootstrap method. Categorical language dominance and mean LI were analyzed. Results: Mean WA LI was lower for subjects with a mesial temporal focus compared to a frontal focus (p=0.04) and categorically, there was a greater proportion of atypical language in WA for subjects with a mesial temporal focus compared to a frontal focus (?2=4.37, p=0.04). WA LI did not differ for subjects with a neocortical focus compared to a mesial focus or a frontal focus (p>0.10). Mean IFG LI and proportion of atypical language in IFG were similar across seizure focus groups (p>0.10). Age and age of onset were not correlated with mean laterality in WA or IFG (p>0.10). Epilepsy duration tended to be negatively correlated with WA LI (r=-0.18, p=0.10), but not IFG LI (p=0.38). Conclusions: Temporal lobe seizure focus appears to have wide-ranging effects on the distributed language system; the effects of a frontal lobe focus are less pronounced on posterior networks.