title: Complex patterns of spatially extended generators of epileptic activity: Comparison of source localization methods cMEM and 4-ExSo-MUSIC on high resolution EEG and MEG data.
abstract: Electric Source Imaging (ESI) and Magnetic Source Imaging (MSI) of EEG and MEG signals are widely used to determine the origin of interictal epileptic discharges during the pre-surgical evaluation of patients with epilepsy. Epileptic discharges are detectable on EEG/MEG scalp recordings only when associated with a spatially extended cortical generator of several square centimeters, therefore it is essential to assess the ability of source localization methods to recover such spatial extent. In this study we evaluated two source localization methods that have been developed for localizing spatially extended sources using EEG/MEG data: coherent Maximum Entropy on the Mean (cMEM) and 4th order Extended Source Multiple Signal Classification (4-ExSo-MUSIC). In order to propose a fair comparison of the performances of the two methods in MEG versus EEG, this study considered realistic simulations of simultaneous EEG/MEG acquisitions taking into account an equivalent number of channels in EEG (257 electrodes) and MEG (275 sensors), involving a biophysical computational neural mass model of neuronal discharges and realistically shaped head models. cMEM and 4-ExSo-MUSIC were evaluated for their sensitivity to localize complex patterns of epileptic discharges which includes (a) different locations and spatial extents of multiple synchronous sources, and (b) propagation patterns exhibited by epileptic discharges. Performance of the source localization methods was assessed using a detection accuracy index (Area Under receiver operating characteristic Curve, AUC) and a Spatial Dispersion (SD) metric. Finally, we also presented two examples illustrating the performance of cMEM and 4-ExSo-MUSIC on clinical data recorded using high resolution EEG and MEG. When simulating single sources at different locations, both 4-ExSo-MUSIC and cMEM exhibited excellent performance (median AUC significantly larger than 0.8 for EEG and MEG), whereas, only for EEG, 4-ExSo-MUSIC showed significantly larger AUC values than cMEM. On the other hand, cMEM showed significantly lower SD values than 4-ExSo-MUSIC for both EEG and MEG. When assessing the impact of the source spatial extent, both methods provided consistent and reliable detection accuracy for a wide range of source spatial extents (source sizes ranging from 3 to 20cm2for MEG and 3 to 30cm2for EEG). For both EEG and MEG, 4-ExSo-MUSIC localized single source of large signal-to-noise ratio better than cMEM. In the presence of two synchronous sources, cMEM was able to distinguish well the two sources (their location and spatial extent), while 4-ExSo-MUSIC only retrieved one of them. cMEM was able to detect the spatio-temporal propagation patterns of two synchronous activities while 4-ExSo-MUSIC favored the strongest source activity. Overall, in the context of localizing sources of epileptic discharges from EEG and MEG data, 4-ExSo-MUSIC and cMEM were found accurately sensitive to the location and spatial extent of the sources, with some complementarities. Therefore, they are both eligible for application on clinical data.
authors: Multimodal Functional Imaging Lab, Biomedical Engineering Dpt., McGill University , Montreal, Canada. Electronic address: rasheda.chowdhury@mail.mcgill.ca.
authors: R A
authors: RA
authors: Chowdhury
authors: INSERM, U1099, 35000 Rennes, France; Université de Rennes 1, Laboratoire de Traitement du Signal et de l'Image, 35000 Rennes, France.
authors: I
authors: I
authors: Merlet
authors: Department of Fundamental and Clinical Neurosciences, University of Geneva, Switzerland.
authors: G
authors: G
authors: Birot
authors: Neurology and Neurosurgery Department, Montreal Neurological Institute (MNI), McGill University, Montreal, Canada.
authors: E
authors: E
authors: Kobayashi
authors: INSERM, U1099, 35000 Rennes, France; Université de Rennes 1, Laboratoire de Traitement du Signal et de l'Image, 35000 Rennes, France; Neurology Department, CHU de Rennes, France.
authors: A
authors: A
authors: Nica
authors: INSERM, U1099, 35000 Rennes, France; Université de Rennes 1, Laboratoire de Traitement du Signal et de l'Image, 35000 Rennes, France; Neurology Department, CHU de Rennes, France.
authors: A
authors: A
authors: Biraben
authors: INSERM, U1099, 35000 Rennes, France; Université de Rennes 1, Laboratoire de Traitement du Signal et de l'Image, 35000 Rennes, France.
authors: F
authors: F
authors: Wendling
authors: Département de Genie Electrique, Ecole de Technologie Supérieure, Canada.
authors: J M
authors: JM
authors: Lina
authors: INSERM, U1099, 35000 Rennes, France; Université de Rennes 1, Laboratoire de Traitement du Signal et de l'Image, 35000 Rennes, France; INRIA, Centre Inria Rennes - Bretagne Atlantique, 35042 Rennes Cedex, France.
authors: L
authors: L
authors: Albera
authors: Multimodal Functional Imaging Lab, Biomedical Engineering Dpt., McGill University , Montreal, Canada; Neurology and Neurosurgery Department, Montreal Neurological Institute (MNI), McGill University, Montreal, Canada; Physics Dpt., PERFORM Centre, Concordia University, Canada.
authors: C
authors: C
authors: Grova
mesh_terms: D002540:Cerebral Cortex / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D004569:Electroencephalography / Q000379:methods* / Q000592:standards; D004827:Epilepsy / Q000175:diagnosis*; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods* / Q000592:standards
keywords: 4-ExSo-MUSIC; EEG/MEG source localization; Higher order statistics; Interictal epileptic discharges; Maximum entropy on the mean; Neural mass model