Abstracts

Rationale: Epilepsy surgery is an effective treatment for seizure control but post-surgical language deficits may occur. Pre-operative functional MRI (fMRI) language testing may be useful for investigating post-operative naming and fluency outcomes. We sought to determine whether regional fMRI lateralization changes following epilepsy surgery.Methods: Sixteen healthy volunteers (mean age 22.1 +/- 3.1 years) and twenty-three patients (mean age 35.7 +/- 10.9 years) referred to the Clinical Epilepsy Section, NINDS, NIH for evaluation of intractable epilepsy completed repeated or pre-/post-operative 3T BOLD fMRI language mapping using an auditory description decision task (ADT) and an auditory category word decision task (AUDCAT) (n=16). The majority of participants were right-handed; two patients (both left resection) were left-handed. Regional laterality indices (LI) for each task were calculated for inferior frontal gyrus (IFG), midfrontal gyrus (MFG) and Wernicke’s Area (WA). Language dominance was determined by regional LI >[0.25] on ADT; patients with LI < -0.25 in one region, but > 0.25 in another, were classified as ‘mixed’. Wilcoxon Signed Rank tests were performed to compare pre- and postoperative LI.Results: Controls had no significant LI change (ADT or AUDCAT) in any region on repeated scans. For the patient group, pre-operatively 19 patients were left dominant for language, two were right dominant, and two mixed. One left-handed patient had mixed, and one right dominance on ADT. Ten patients had left, and 13 right temporal lobectomy. Mean resection volume was 19.3 +/- 8.8 CC. A Wilcoxon signed rank test showed that there was a significant pre- to post-operative change in AUDCAT MFG LI (median pre-operative LI = 0.07, median post-operative LI = -0.130, p <0.05), but no significant LI change for any other ROIs for AUDCAT or ADT (p >.05). Post-operatively, 20 subjects were left dominant, two right dominant, and one mixed. Three patients had changes in language dominance with one overt (right to left) change in dominance. One left dominant patient developed mixed dominance after left temporal lobectomy; a right dominant patient became left dominant after right temporal lobectomy (due to a change from AI -0.50, to 0.40 in IFG, and -0.29 to 0.57 in MFG); a left-handed mixed dominance patient became right dominant after left temporal lobectomy. FMRI dominance changes were not related to changes on the Boston Naming or Controlled Oral Word Association tests.Conclusions: Although surgery influenced language laterality only in a minority of patients, effects suggested increasing dominance contralateral to resection, perhaps indicating compensation and reorganization, Greater right hemisphere MFG activation post-surgically may represent compensatory language function