This simulated magnetoencephalographic study was designed to determine the variability in source parameters with real subject background activity when applying multidipole spatial-temporal dipole analyses, for which the correct model was compared with undermodeled and overmodeled cases. The simulated sources were created from patches of the cortical surface of each subject's MRI. One- and two-source frontal lobe spikes were generated in two cortical regions seen commonly in frontal lobe epilepsy patients tested at our site (orbital frontal and premotor cortex). In general, the modeling results were adequate for the correct model order and the correct model order plus one. In addition, if the localization error was less than 10 mm from the simulated source, the peak latency of the spike and orientation were very reliable, but the peak amplitude was not. The additional source in the overmodeled condition, on the other hand, was not localized reliably across the different epochs within subjects. The results suggest that consistency of the spike localization and inconsistency of other sources will allow one to determine reliably the appropriate model order in real data, and therefore determine single and multifocal spike generators.
Departments of *Radiology,†Neurology, and‡Neuroscience, University of New Mexico School of Medicine;§New Mexico VA Health Care System, Albuquerque, New Mexico; and |Biophysics Group, Los Alamos National Laboratory, Los Alamos, New Mexico, USA
Supported in part by National Institutes of Health/NCRR COBRE grant 5-P20-RR15636-02; the Department of Radiology, University of New Mexico School of Medicine; and the Research Service of the New Mexico VA Healthcare System, Albuquerque, NM, USA.
Presented in part at the 13th International Conference on Biomagnetism; Jena, Germany; August 10 to 14, 2002.
Address correspondence and reprint requests to Dr. Jerry J. Shih, Departments of Neurology and Neuroscience, University of New Mexico, 915 Camino de Salud NE, Albuquerque, NM 87131 USA; e-mail: firstname.lastname@example.org