Abstracts

Magnetoencephalography/Magnetic Source Imaging (MSI) is a completely non-invasive technique, which has recently been used to lateralize and localize language specific regions in the brain (Papanicolaou et al., 2004). To date, the Wada Test or Intracarotid Amobarbital Procedure (IAP) has been the gold standard in determining speech/language lateralization for presurgical planning. The purpose of this research is to validate the use of MSI to lateralize language in patients who have also undergone the IAP at the Minnesota Epilepsy Group., The sample consisted of 32 subjects (age 15-61 years) with epilepsy and/or brain tumor who had undergone presurgical evaluation at the Minnesota Epilepsy Group. For the IAP, language lateralization was determined by the patient[apos]s ability to produce and/or understand meaningful speech at maximal drug effect (i.e., zero motor response). For MSI language mapping, an auditory word recognition task was used to activate language-specific cortex. For both methods, an asymmetry index was calculated with cut-off scores designating left, right, or bilateral language representation. The MEG unit consisted of a 148-channel Magnes 2500 WH system (4-D Neuroimaging, San Diego, CA) housed in a magnetically shielded room. MSI language analysis was done blind to the IAP results. A single equivalent current dipole (ECD) model across each whole hemisphere was used in the analysis of language data. Groups were analyzed using parametric and non-parametric statistics., MSI was consistent with the IAP in identifying the primary language hemisphere in 88% of the cases, based on independent laterality judgments for each procedure. There were two completely discordant cases; one showing left language dominance by IAP and right dominance by MSI and a second showing the opposite. The concordance between the IAP and MSI in determining whether language resides in the hemisphere to be treated was 84% with sensitivity and specificity values of 100% and 50%, respectively (p [lt] .001)., The IAP and MSI show a concordance rate of 88% in identifying the primary language hemisphere when relative degree of language lateralization is taken into account. The concordance between the IAP and MSI to detect language in the hemisphere being considered for surgery was 84%, with the MSI showing five false negatives. Two cases did show complete discordance of language lateralization by the two procedures. An unsually high (38%) rate of atypical (bilateral or right dominant) IAP language cases in this sample may partly explain some of the discrepant findings. Moreover, restricting MSI language source localization to only the temporal lobes may improve concordance of the two methods. These results represent an ongoing research project with the goal of establishing MSI as a viable replacement for the IAP in the presurgical determination of language lateralization., (Supported by United Hospital Foundation.)