Hemodynamic responses to interictal epileptiform discharges in children with symptomatic epilepsy

PURPOSE: Simultaneous electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) (EEG-fMRI) recording is a noninvasive tool for investigating epileptogenic networks. Most EEG-fMRI studies in epilepsy have been performed in adults. Childhood epilepsies, however, differ from those in adults due to interactions between epileptogenic and developmental processes. The purpose of this study was to investigate EEG-fMRI in children with lesional epilepsies. METHODS: Thirteen children with symptomatic epilepsy underwent a 20-min EEG-fMRI acquisition at 3 T under sedation-induced sleep. Statistical analysis was performed using the timing of spikes as events, modelled with hemodynamic response functions (HRFs) that peaked at 3, 5, 7, and 9 s after the spike. RESULTS: Each spike type was analyzed separately, resulting in 25 studies. In 84% of the studies, blood oxygenation level-dependent (BOLD) responses were localized in the lesion or brain area presumably generating spikes. Activation (positive BOLD) corresponding with the lesion was seen in 20% and deactivation (negative BOLD) in 52% of the studies. In the area of spike generation, activation was found in 48% of studies and deactivation in 36%. CONCLUSIONS: Despite the necessarily short recording times (20 min), good results could be obtained from the EEG-fMRI recordings, performed in sedated children using a high field scanner and individual HRFs. In contrast to studies in adults, deactivations in the lesion and the irritative zone were more common than activations. The impact of age, sleep, and sedation on the BOLD response might explain these findings, but future studies in children should not disregard the importance of deactivations in relation to the epileptogenic network.