Magnetoencephalography (MEG) is the magnetic counterpart of EEG.
History of MEG
The first MEG recordings of brain activity were measured in 1968 by David Cohen et al. at the MIT in Boston (Cohen 1968). Cohen was able to detect the magnetic equivalent of the electric alpha-rhythm using conventional coils. To record the exceptionally small magnetic fields produced inside the brain, the measurement was done in a magnetically shielded room. The data was averaged, time-locked to the simultaneously recorded EEG, to increase the signal-to-noise ratio.
In 1962, the British physicist Brian David Josephson, then a graduate student, discovered what was later called the Josephson Effect. This describes the phenomenon of current flow across two superconductors separated by a very thin insulating barrier.
The principle of MEG
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Modern MEG systems cover the entire head with coils that pick up the small magnetic field changes produced by the brain. The picture shows the sensor arrangement of the Elekta Neuromag 306 whole-head system. Earlier systems consisted of a single channel, eight channels or 37 channels (BTi Magnes).
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Lorem ipsum dolor sit amet, consectetuer adipiscing elit. In accumsan dictum purus. Mauris nec massa eget nulla suscipit tincidunt. Ut rutrum molestie velit. Etiam rutrum. Nullam nonummy. Nulla facilisi. Aliquam dignissim turpis vitae tellus. In sagittis. Suspendisse nulla. Duis ornare congue mauris. In et pede. Fusce viverra euismod nisl. Fusce ac ante non sem aliquet ultrices. Nam ultrices metus a mauris. Mauris magna nulla, eleifend sed, scelerisque ac, ornare feugiat, urna.
MEG software
BrainStorm is a Matlab toolbox for MEG and EEG visualization and analysis.
NUTMEG uses an adaptive eigenspace vector beamformer to reconstruct the time series of neural activity at every grid point within a brain volume of interest. A short paper describing NUTMEG appeared in Neurology and Clinical Neurophysiology 2004. pdf
BESA (Brain Electrical Source Analysis). Software for source analysis and dipole localization in EEG and MEG research. For combined analysis of MEG / EEG and MRI / fMRI data, BESA has an easy link to BrainVoyager. Besa is a commercial programme and runs only under Windows.
SAM (Synthetic Aperture Magnetometry), provided by CTF.
Own work
Sörös P, Dziewas R, Manemann E, Teismann IK, Lütkenhöner B. No indication of brain reorganization after unilateral ischemic lesions of the auditory cortex. Neurology 2006;67:1059-1061. PubMed Reprint
Sörös P, Michael N, Tollkötter M, Pfleiderer B. The neurochemical basis of human cortical auditory processing: Combining proton magnetic resonance spectroscopy and magnetoencephalography. BMC Biology 2006;4:25. PubMed Reprint
Sörös P, Cornelissen K, Laine M, Salmelin R. Naming actions and objects: cortical dynamics in healthy adults and in an anomic patient with a dissociation in action/object naming. Neuroimage. 2003;19(4):1787-801. PubMed Reprint
Sörös P, Teismann I, Manemann E, Michael N, Pfleiderer B, Ross B, Pantev C. Interindividual and interhemispheric differences of brain function: an MEG study of auditory short-term adaptation. In: Nowak H, Haueisen J, Gießler F, Huonker R, editors. Proceedings BIOMAG 2002, 13th International Conference on Biomagnetism. Berlin: VDE; 2002. p. 125 – 127. Reprint
Sörös P, Knecht S, Bantel C, Imai T, Wüsten R, et al. Functional reorganization of the human primary somatosensory cortex after acute pain demonstrated by magnetoencephalography. Neurosci Lett. 2001;298(3):195-8. PubMed Reprint
Sörös P, Knecht S, Manemann E, Teismann I, Imai T, Lütkenhöner B, Pantev C. Hemispheric asymmetries for auditory short-term habituation of tones? In: Nenonen J, Ilmoniemi RJ, Katila T, editors. Biomag2000, Proceedings 12th International Conference on Biomagnetism. Espoo: Helsinki University of Technology; 2001. p. 47 – 49. Reprint
Sörös P, Knecht S, Imai T, Gürtler S, Lütkenhöner B, et al. Cortical asymmetries of the human somatosensory hand representation in right- and left-handers. Neurosci Lett. 1999;271(2):89-92. PubMed Reprint
Further Reading
Cohen D. Magnetoencephalography: evidence of magnetic fields produced by α-rhythm currents. Science. 1968 Aug 23;161(843):784-6.
Cohen D. Boston and the history of biomagnetism. Neurology and Clinical Neurophysiology 2004:114 pdf
Josephson BD. The discovery of tunnelling supercurrents. Nobel Lecture 1973. pdf
Vrba J. Multichannel squid biomagnetic systems. 2000. pdf
Introduction to MEG
Biomagnetism by Jaakko Malmivuo and Robert Plonsey, online edition. This book is an excellent introduction to the physiology of biomagnetic phenomena, to the methods of biomagnetic recording and to the applications of those methods.
The basic mechanisms behind MEG. Short text provided by 4D Neuroimaging. pdf
A general overview about MEG and its applications. Presentation provided by 4D Neuroimaging, 10 MB. pdf
An MEG examination, step by step. Short text provided by 4D Neuroimaging. pdf
Links
Magnetoencephalography at Wikipedia
SQUIDs at Wikipedia
Biomagnet Abstracts Database. A small collection of MEG papers.