What is Magnetoencephalography (MEG)?

MEG unit

MEG is a state-of-the-art non-invasive functional brain imaging technology. This extremely sensitive technology measures very faint magnetic fields produced by electrical neuronal activity at numerous different positions around the head (a distribution of about 100 to 300 points). It allows researchers to track moment-to-moment brain activity and determine when, where, and how the brain functions enable sensation, perception, memory, language, decision-making, thinking, and controlled action.

MEG technology is the safest of all the brain imaging techniques. Because it is totally passive and deposits no energy in, and does not even touch, the individual whose brain activity is being monitored, MEG is particularly important for routine use in basic research, for clinical research, and especially in investigations involving young children.

EM fields Image

The advantage of sensing magnetic fields – as opposed to the related electrical fields, as is done in Electroencephalography(EEG) – is that they pass through the skull and other tissues between the active neurons and the MEG sensors without distortion (unlike EEG, where substantial signal smearing occurs). This property of magnetic fields enables accurate and precise localization of neuronal sources in the brain.

MEG Dipole image

MEG uses a high temporal sampling rate – e.g. 1000 samples per second (hertz, Hz), or even faster. This fine temporal resolution (in the order of milliseconds), contrasts with that of functional Magnetic Resonance Imaging (fMRI), which essentially senses blood oxygen changes (indicative of brain activity), a much slower response system in the human brain (with lags of seconds).

MEG overlaid on anatomical MRI

This combination of the fine temporal and spatial resolutions of modern MEG systems allows neuroscientists to discover where (to within a few millimeters) and when (to less than one thousanth of a second) the brain is active in various situations. This exceeds the capabilities of any other non-invasive brain imaging method (fMRI, EEG, PET, SPECT, NIRS). Furthermore, the MEG data collected can be combined with, and overlayed on, that from anatomical MRI, fMRI, and even simultaneous EEG scans to provide an even more complete spatio-temporal analysis of brain activity.

Links :

University of Montreal MEG Laboratory website
Canada MEG Consortium website

Last update: Feb. 11, 2011.