Abstracts

Rationale: Functional magnetic resonance imaging (fMRI) is an effective and noninvasive tool that can be used to determine localization of language networks in the frontal and temporal regions. We aimed to determine the differences in lateralization induced by reading and listening paradigms, and whether early seizure onset would cause a higher incidence of atypical reading dominance due to the late development of this skill. Methods: 101 patients with left focal epilepsy (46 females, 55 males; mean age 23.2 yrs, range 8-50 years; mean age of seizure onset 11.6 yrs, range 0-46 yrs; mean duration of epilepsy 11.6 yrs, range 0-47.5 yrs; 80.2% right-handed, 15.8% left-handed, 4% ambidextrous) and 24 right handed normal controls (10 females, 14 males; mean age 29.2 yrs, range 21-56 yrs) performed reading and listening paradigms using 3T BOLD fMRI. Language activation was characterized by region of interest (ROI) laterality indices: Wernicke's area (WA; BA 21, 22, 39), inferior frontal gyrus (IFG; BA 44, 45, 47), and middle frontal gyrus (MFG; BA 9, 46). Language dominance was deemed left or atypical (LI≤0.20 atypical). Results: The reading task exhibited more left lateralization than the listening task for MFG (t= -2.99, p=.003). There was a trend of weaker left lateralization in patients than controls (p=0.061); More patients had atypical lateralization than controls. Patients and controls LIs differed from each other (main effect), but this is not due to different ROIs or tasks (F=6.59, p=0.011). Differences in LI between patients and controls were significant in WA (t=2.38, p=.021) in the reading task and WA (t= 4.41, p=0.00; χ2=5.19, p=0.023) and MFG (t=3.25, p=0.002; χ2=8.29, p=0.004) in the listening task. To determine that epilepsy rather than pathological tissue caused the atypical LI, LIs of patients with normal MRIs were compared to controls. Patients had weaker left LI during the listening task in WA (t=3.46, p=0.001). Both findings were confirmed when separating LIs into two categories (atypical and typical): listening in WA (χ2=5.50, p=0.019) and listening in MFG (χ2=3.98, p=0.046). Unlike the listening task, patients with early seizure onset (<6 yrs) had a higher LIs than patients with late seizure onset during the reading task, significant for WA (t= -2.03, p=.045; χ2=6.77, p=0.009) and lower LI (p<0.045). Conclusions: We found modest differences across language tasks. Patients had weaker left lateralization than controls, not dependent on MRI pathology, task, or region. Older age of seizure onset was associated lower lateralization in WA during the reading task and provides modest evidence for reorganization of reading networks associated with late development of reading skills.