Abstracts

Rationale: Seizures in childhood absence epilepsy (CAE) are characterized electrographically by epochs of 3-4 Hz spike-and-wave discharges and semiologically by impaired consciousness. Although absence seizures have historically been categorized as generalized events, recent work has demonstrated a complex timecourse of focal changes in the brain, particularly within the attention network including the orbital/medial frontal cortex, medial/lateral parietal cortex and thalamus. In addition to subtle electrographic differences in absence epilepsy across seizures and between patients, considerable variability also exists in ictal blood oxygen level-dependent (BOLD) signal changes and behavioral performance. We propose that the selective disruption of attentional networks, as captured by BOLD signal changes, is related to the degree of behavioral impairment during absence seizures. Methods: Using simultaneous electroencephalography and functional magnetic resonance imaging (EEG-fMRI), we examined ictal changes for 175 seizures in 13 pediatric patients with CAE. During each scan, patients performed a continuous performance task (CPT) or a simpler repetitive tapping task to measure impaired attention. BOLD signals changes were analyzed using statistical parametric mapping (SPM) and in-house software. Results: As expected, patients performance during SWD was impaired, and this impairment was more pronounced during CPT than RTT. fMRI changes seen during seizures were consistent with those demonstrated in previous studies. Specifically, we observed a complex sequence of changes in orbital frontal, parietal, and other cortical areas as well as the thalamus. The timecourse of ictal BOLD changes and behavioral performance were highly variable across patients and seizures and were not obviously correlated with the EEG measures. An analysis of the EEG recordings revealed a possible link between seizure duration and the degree of ictal impairment. Interestingly, however, omission errors were committed even during brief spike-wave seizures. Conclusions: Focal fMRI changes in cortical and subcortical attention structures appear to be related to variability in task performance during seizures. This relationship can shed light on the mechanism by which absence seizures cause impaired consciousness and could guide development of targeted therapies.