Language lateralization in temporal lobe epilepsy: A functional magnetic resonance imaging study

TLE is the most frequent type of epilepsy in adult population. Preoperativelocalization and assesment of laterality of language areas are essential in epilepsysurgery to prevent postoperative neurological deficitis. FMRI is a promisingimaging tool for assesment of laterality of language areas. The aim of this study isto develop a clinical FMRI language design for presurgical evaluation of TLEpatients.Fifteen patients with TLE and 15 healthy, volunteers were included in thestudy. Following the acquisition of high-resolution T1-weighted anatomicalreference images, functional imaging was obtained by gradient-echo EPIsequence. Two different FMRI paradigms as Verb Generation Task-1 (VGT-1),Verb Generation Task-2 (VGT-2) were used in each subject for the lateralizationof the language areas. VGT-1 has passive baseline conditions with true rests.Baseline conditions of VGT-2 include active state with the use of nonsense words.Group analyses and individual-subject analysis were done by Brain Voyager QXsoftware.By using VGT-1, largely bilateral activations in frontal, temporal andparietal regions were obtained. With VGT-2, strongly left lateralized activationsin frontal and temporal regions were obtained. During VGT-2, parietal regionswere not activated and when compared with VGT-1, frontal and temporalactivation signals were small in size. False-negative activation can be seen whenonly VGT-II was used. However, VGT-2 provided more robust activations insuperior temporal gyrus then VGT-1. Superior temporal gyrus is known as atarget region for epilepsy surgery that has a key role in receptive languagefunction.Our results show that VGT-2 can be used as a complementy technique ofVGT-1 for accurate lateralization of all critical language cortical areas.