Are Epilepsy-Related fMRI Components Dependent on the Presence of Interictal Epileptic Discharges in Scalp EEG?
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Spatial independent component analysis (ICA) is increasingly being used to extract resting-state networks from fMRI data. Previous studies showed that ICA also reveals independent components (ICs) related to the seizure onset zone. However, it is currently unknown how these epileptic ICs depend on the presence of interictal epileptic discharges (IEDs) in the EEG. The goal of this study was to explore the relation between ICs obtained from fMRI epochs during the occurrence of IEDs in the EEG and those without IEDs. fMRI data sets with co-registered EEG were retrospectively selected of patients from whom the location of the epileptogenic zone was confirmed by outcome of surgery (n = 8). The fMRI data were split into two epochs: one with IEDs visible in scalp EEG and one without. Spatial ICA was applied to the fMRI data of each part separately. The maps of all resulting components were compared to the resection area and the EEG–fMRI correlation pattern by computing a spatial correlation coefficient to detect the epilepsy-related component. For all patients, except one, there was a remarkable resemblance between the epilepsy-related components selected during epochs with IEDs and those without IEDs. These findings suggest that epilepsy-related ICs are not dependent on the presence of IEDs in scalp EEG. Since these epileptic ICs showed partial overlap with resting-state networks of healthy volunteers (n = 10), our study supports the need for new ways to classify epileptic ICs.
KeywordsEpilepsy Resting-state fMRI EEG–fMRI Independent component analysis Interictal epileptiform discharges Epileptic independent component
Blood oxygenation level-dependent
EEG–correlated functional MRI
Independent component analysis
Interictal epileptiform discharges
This study is part of the Central Nervous System and Imaging (CSI) project that has received funding from the ENIAC Joint Undertaking (Grant no. 120209). The authors would like to thank Mike van der Mierden, Marlies Dolmans, Ine Keulen for the annotation of the EEG data. Furthermore, we would like to thank Jan Verwoerd from Philips Medical Systems (Best, the Netherlands) for his assistance regarding the MR imaging sequences and Frans Leijten from University Medical Center Utrecht for providing the postoperative MRIs.
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