Altered brain rhythms and functional network disruptions involved in patients with generalized fixation-off epilepsy
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Generalized Fixation-off Sensitivity (CGE-FoS) patients present abnormal EEG patterns when losing fixation. In the present work, we studied two CGE-FoS epileptic patients with simultaneous EEG-fMRI. We aim to identify brain areas that are specifically related to the pathology by identifying the brain networks that are related to the EEG brain altered rhythms. Three main analyses were performed: EEG standalone, where the voltage fluctuations in delta, alpha, and beta EEG bands were obtained; fMRI standalone, where resting-state fMRI ICA analyses for opened and closed eyes conditions were computed per subject; and, EEG-informed fMRI, where EEG delta, alpha and beta oscillations were used to analyze fMRI. Patient 1 showed EEG abnormalities for lower beta band EEG brain rhythm. Fluctuations of this rhythm were correlated with a brain network mainly composed by temporo-frontal areas only found in the closed eyes condition. Patient 2 presented alterations in all the EEG brain rhythms (delta, alpha, beta) under study when closing eyes. Several biologically relevant brain networks highly correlated (r > 0.7) to each other in the closed eyes condition were found. EEG-informed fMRI results in patient 2 showed hypersynchronized patterns in the fMRI correlation spatial maps. The obtained findings allow a differential diagnosis for each patient and different profiles with respect to healthy volunteers. The results suggest a different disruption in the functional brain networks of these patients that depends on their altered brain rhythms. This knowledge could be used to treat these patients by novel brain stimulation approaches targeting specific altered brain networks in each patient.
KeywordsFixation-off Simultaneous EEG-fMRI Resting-state networks EEG-informed fMRI ICA
The authors would like to thank Ricardo Bruña and Elena Molina for productive discussions on the applied analysis in this work. Fudnación CIEN-Fundacion Reina Sofia, Centro de Investigación en red Ciber-BBN, projects MADR.IB S-SAL-312-2006 by Comunidad de Madrid and TEC2009-14587-C03-02 by Spanish Government, Consejo Social of Universidad Politecnica de Madrid and fellowship RR02/2009 (UPM) have provided funds towards this project.
Ana Beatriz Solana Sánchez declares that she is employee of General Electric Global Research Center. However, this research work was carried out while doing her PhD in the Center for Biomedical Technology in Madrid under public funding sources detailed in the acknowledgements.
Kenia Martínez, Juan Antonio Hernández-Tamames, Victoria San Antonio-Arce, Rafael Toledano, Irene García-Morales, Juan Alvárez-Linera, Antonio Gil-Nágel and Francisco del Pozo declare that they have no conflict of interest.
All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, and the applicable revisions at the time of the investigation. Informed consent was obtained from all patients for being included in the study.
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