Abstracts

Rationale: Presurgical mapping using MEG in children with medically intractable seizures is fraught with difficulty. Children with epilepsy often have atypical motor and language activation patterns (1)(2). Given the gravity of the situation, identifying reliable and reproducible methods for determing neurophysiologic effects associated with epileptic foci are particularly vital. In this study, we evaluated using the temporal pattern of somatosensory response to predict epileptic hemispheric involvement. Methods: Eighteen pediatric patients (18) with medically intractable epilepsy were examined at the Neuroscience Institute at Le Bonheur Children s Hospital (Memphis, TN). A whole head Magnes 3600 WH (248-channel) (4D Neuroimaging, Inc., San Diego, CA) was used to identify the somatosensory function areas. MEG data was analyzed using the equivalent current dipole method implemented in SPM8 (www.fil.ion.ucl.ac.uk/spm). Data was coregistered to the MNI305 3D T1 template for conformation of MSI localizations. Using Posterior Probability Maps (PPM) of source localized SSEP s, we identified the activated voxels in Brodman areas 2 and 3. We then plotted the time course of those voxels and selected the time of maximal activation. Results: Three patients demonstrated unilateral activation and were excluded from the study. Fourteen of the remaining 15 patients demonstrated significant delay in the time of maximal activation compared to the contralateral side. In eleven of the fourteen, the delayed side was also the same hemisphere known to contain the epileptic foci. No significant difference was found in a Left vs. Right comparison. No correlation was found with age or handiness. Conclusions: This preliminary study demonstrates the promising potential of using the temporal characteristics of the equivalent current dipole to determine hemispheric localization of epileptic foci. This method is important in that it might be used in cases when a resting state recording could not be acquired or is technically unsuccessful.