Point and distributed current density analysis of interictal epileptic activity recorded by magnetoencephalography

Equivalent current dipole (ECD) analysis and fully three-dimensional distributed source solutions have been applied to interictal multichannel magnetoencephalographic recordings of a patient with complex partial epilepsy (CPE). Averaged signals were used. At certain instances ECD solutions could be found with a very high cross-correlation coefficient between the measurements and the field, produced by the current dipole solution, typically in excess of 0.97. At these instances a highly localized distribution, very close to the ECD location, was obtained from the distributed source analysis. The ECD solution started to move when the distributed source solution began to develop activity at more than one centre. This clearly contrasted with the way the activity of the distributed source solutions changed, which turned out to be highly stable. Stringent selection criteria for using the different solutions therefore seem mandatory, especially in identifying pathological areas and volumes of the human brain.