title: Minimum norm estimates in MEG can delineate the onset of interictal epileptic discharges: A comparison with ECoG findings.
abstract: The analysis of epileptic discharges in magnetoencephalography with minimum norm estimates (MNE) is expected to provide more precise localization of epileptic discharges compared with electroencephalographic estimations. However, the clinical feasibility of MNE remains unclear. In this study, we aimed to elucidate the onset and propagation patterns of interictal spikes using MNE. Seven patients with intractable epilepsy whose epileptogenicity was assumed to exist in the convexity of the cerebral cortex were studied. For MNE and electrocorticography (ECoG), we characterized the propagation patterns of interictal epileptic discharges according to the area in which they originated and where they extended; we then examined whether the propagation patterns observed in MNE were identified by ECoG. We also examined the relationship between the positions of spikes estimated by the equivalent current dipole (ECD) method and MNE. Among the seven patients, nine propagation patterns of epileptic discharges were observed by MNE, all of which were also identified by ECoG. In seven patterns, the epileptic activity propagated around the initial portion. However, in two patterns, the center of activities moved according to propagation with maintained activity of the initial portion. The locations of spikes identified by the ECD method were within the areas estimated by MNE when the epileptic activity propagated. However, the ECD method failed to detect onset activities identified by MNE in three of nine patterns. Thus, MNE is more useful as a means of presurgical evaluation for epilepsy than the ECD method because it can delineate the onset of epileptic activities as shown in ECoG.
authors.affiliation: Department of Neurology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, Japan ; Department of Clinical Neurophysiology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kanamori
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Shigeto
authors.forename: Naruhito
authors.initials: N
authors.lastname: Hironaga
authors.forename: Koichi
authors.initials: K
authors.lastname: Hagiwara
authors.forename: Taira
authors.initials: T
authors.lastname: Uehara
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Chatani
authors.forename: Ayumi
authors.initials: A
authors.lastname: Sakata
authors.forename: Kimiaki
authors.initials: K
authors.lastname: Hashiguchi
authors.forename: Takato
authors.initials: T
authors.lastname: Morioka
authors.forename: Shozo
authors.initials: S
authors.lastname: Tobimatsu
authors.forename: Jun-Ichi
authors.initials: J
authors.lastname: Kira
keywords: Dynamic statistical parametric mapping (dSPM); Electrocorticography (ECoG); Epilepsy; Interictal discharge; Magnetoencephalography (MEG); Minimum norm estimates (MNE)