Mapping the signal-to-noise-ratios of cortical sources in magnetoencephalography and electroencephalography

• Published in: Human brain mapping Vol. 30; no. 4; pp. 1077 - 1086
• Main Authors: Goldenholz, Daniel M., Ahlfors, Seppo P., Hämäläinen, Matti S., Sharon, Dahlia, Ishitobi, Mamiko, Vaina, Lucia M., Stufflebeam, Steven M.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.04.2009; Wiley-Liss
• Subjects: Action Potentials - physiology; Adult; Biological and medical sciences; brain; Brain Mapping; Cerebral Cortex - physiology; cortex; dipole; EEG; Electric Stimulation; Electroencephalography; epilepsy; Evoked Potentials - physiology; Female; forward model; Hamartoma - pathology; Humans; Hypothalamus - physiopathology; Investigative techniques, diagnostic techniques (general aspects); Magnetoencephalography; Male; Medical sciences; MEG; Models, Neurological; Nervous system; Nervous system (semeiology, syndromes); Nervous system as a whole; Neurology; Noise; Radiodiagnosis. Nmr imagery. Nmr spectrometry; Signal Processing, Computer-Assisted; simulation; SNR; Young Adult; cortex; Cartography; Nervous system diseases; Radiodiagnosis; Magnetoencephalography; Epilepsy; EEG; forward model; Central nervous system; Electrophysiology; Electroencephalography; brain; MEG; Cerebral disorder; Encephalon; Simulation; SNR; Central nervous system disease; Dipole; Models; Signal to noise ratio
• ISSN: 1065-9471; 1097-0193; 1097-0193
• DOI: 10.1002/hbm.20571

Although magnetoencephalography (MEG) and electroencephalography (EEG) have been available for decades, their relative merits are still debated. We examined regional differences in signal‐to‐noise‐ratios (SNRs) of cortical sources in MEG and EEG. Data from four subjects were used to simulate focal and extended sources located on the cortical surface reconstructed from high‐resolution magnetic resonance images. The SNR maps for MEG and EEG were found to be complementary. The SNR of deep sources was larger in EEG than in MEG, whereas the opposite was typically the case for superficial sources. Overall, the SNR maps were more uniform for EEG than for MEG. When using a noise model based on uniformly distributed random sources on the cortex, the SNR in MEG was found to be underestimated, compared with the maps obtained with noise estimated from actual recorded MEG and EEG data. With extended sources, the total area of cortex in which the SNR was higher in EEG than in MEG was larger than with focal sources. Clinically, SNR maps in a patient explained differential sensitivity of MEG and EEG in detecting epileptic activity. Our results emphasize the benefits of recording MEG and EEG simultaneously. Hum Brain Mapp 2009. © 2008 Wiley‐Liss, Inc.