Source localization of two evoked magnetic field components using two alternative procedures.

The purpose of this study was to compare the relative efficacy of two methods in assessing the location of the sources of the N100 and P200 components of evoked magnetic fields (EMFs) to transient tone stimuli. EMFs to left ear stimulation, containing both components, were recorded over the right hemisphere of six normal subjects. The magnetic scalp distributions calculated at several adjacent time points, covering the duration of each component's peak, were used to estimate the source parameters of each component. Good estimates of the source of both components were obtained from all magnetic field distributions. The averaged spatial parameters derived from all distributions of each component as well as the parameters derived from the distribution that gave the best source estimate for each component were projected onto magnetic resonance images of subject's head. It was found that the source of each component is located on the superior surface of the temporal lobe and that the source of the P200 component is anterior to the N100 source in all subjects using both procedures.