Abstracts

Rationale: Childhood absence epilepsy (CAE) is characterized by EEG recordings of generalized, bilaterally synchronous 2.5-3.5 Hz spike and wave discharges (SWD) concurrent with behavioral arrest and loss of awareness. Recent clinical studies [1, 2] support a model in which absence seizures rapidly progress from specific cortical foci, rather than occurring as a generalized phenomenon. We used time-resolved magnetoencephalography (MEG) imaging to address whether specific cortical regions initiate absence seizures and if such foci can be pinpointed with this technique. Methods: Through the use of simultaneous MEG and EEG recordings we collected absence seizure activity from a 14 y/o female untreated for CAE. 26 prolonged “interictal” and 15 evoked (elicited by verbal commands to hyperventilate) SWDs were recorded during a two-hour period. Time frequency and beamforming methods were used to analyze the data. Results: 1) The onset and frequency of MEG responses correlated with SWD as recorded in and indexed by the EEG data. MEG SWDs exhibited higher amplitude and longer duration SWDs in frontal sensors compared to occipital sensors. EEG SWDs demonstrated similar time courses and amplitudes across the array. 2) MEG SWDs were typified by a relatively broad-band spectral power representation across many sensors. Time frequency analyses characterized pre-ictal frequency bands (10-18 Hz) that showed increased power prior to the first spike of a SWD. The pattern and degree of activity varied between the ”interictal” and evoked conditions. 3) MEG beamforming analysis revealed that ictal activity within the 3-7 Hz band appeared to progress from specific cortical locations. Conclusions: We identified regions involved in the early discharges which are consistent with those indicated in animal studies of ictal discharges [3], but suggest a larger network of brain interactions. Our data analyses reveal unique frequency bands that may reflect network states preceding stereotypical SWDs. Beamforming analysis revealed complex patterns of activation that may indicate specific trigger zones for initiation of SWD. Our results suggest that limited subsets of brain networks can be revealed by MEG, which may allow a better classification of epilepsy or aid in the discovery of novel pharmacological interventions. Acknowledgements: NIH NRSA FAA017041A from NIAAA to TWH; Wake Forest University Intramural Award to DWG; T32 Training Grant to JRSK References: 1.Craiu, D., S. Magureanu, and W. van Emde Boas, Are absences truly generalized seizures or partial seizures originating from or predominantly involving the pre-motor areas? Some clinical and theoretical observations and their implications for seizure classification. Epilepsy Research, 2006. 70(Supplement 1): p. 141-155. 2.Tucker, D.M., et al., Discharges in ventromedial frontal cortex during absence spells. Epilepsy & Behavior, 2007. 11(4): p. 546-557. 3.Nersesyan, H., et al., Dynamic fMRI and EEG recordings during spike-wave seizures and generalized tonic-clonic seizures in WAG/Rij rats. J Cereb Blood Flow Metab, 2004. 24(6): p. 589-99.