Multiple Source Modeling of the Human Epileptic Spike Complex in the Magnetoencephalogram
Interictal spikes are a common characteristic of human focal epilepsy. These spikes are of both clinical interest as they can help to localize the epileptic focus as well as scientific interest as they provide evidence of altered cortical excitability. As localization by the scalp-EEG is not always conclusive and invasive techniques like stereotaxically placed electrodes or subdurally implanted grid or strip electrodes bear medical risks (e.g. infection, subdural hematoma or intracranial bleeding), new non-invasive techniques are required for the study of the epileptic spike complex. Investigation of the epileptic spike complex with the magnetoencephalogram (MEG) has shown initial promising results and good agreement with localizations obtained from invasive recordings (Barth et al., 1984; Ricci et al., 1987; Rose et al., 1987; Sutherling et al., 1988). Single dipole modeling was applied in these studies as source localization method. However, as evidenced from recordings of the surface of the brain, epileptiform discharges vary both in space in time within an extended epileptogenic zone (Graf et al., 1984) and the interictal spike complex is thus clearly not generated by a single equivalent dipole.
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