Abstracts

Rationale: Most clinical MEG centers record both MEG and EEG, but model only MEG sources. This may be related to the belief that MEG spikes are more prevalent, MEG is more sensitive, or proprietary software limitations. Biophysics would contend, however, that EEG, being sensitive to radial as well as tangential source orientations, would provide complementary data.Methods: We recorded 306 channels of MEG and 25 channels of EEG simultaneously in 130 consecutive patients over 16 months. We inspected the MEG and EEG recordings separately, identified spikes in both, determined if their voltage and/or magnetic fields were dipolar, and segregated them into types based on similar and distinct field topography. We categorized each spike type as 1) having both a model-worthy MEG and EEG field, 2) having only an MEG field, and 3) having only an EEG field.Results: 110 patients (85%) had a total of 301spike types identified (average of 2.7 per patient). 50% of spike types (151) were present in both MEG and EEG. However, 40% of spike types (121) were only evident in EEG and 10% (29) only in MEG. At least one spike type failed to be identified by MEG or EEG in 66% and 23% of patients, respectively. 11 patients had only EEG spikes; 4 patients had only MEG spikes.Conclusions: To obtain an optimal yield of diagnostic information, EEG should also be subjected to source analysis in any clinical MEG study. EEG and MEG data are indeed complementary.