Basics of MEG (Magnetoencephalography)

Screenshots of Brainstorm (neuroimage.usc.edu/brainstorm)

CTF MEG Scanner @ McGill / MNI MEG is a state-of-the-art non-invasive functional brain imaging technology. This extremely sensitive technology measures the faint magnetic fields produced by electrical neuronal activity at numerous different positions around the head (typically about 300 sensor locations). It allows researchers to track moment-to-moment brain activity (at the millisecond time scale, or better) and determine when, where, and how the brain functions enable sensation, perception, memory, language, decision-making, thinking, and controlled action. It also has the unique ability to detect brain dysfunction and dysrhythmia of ongoing brain oscillations, with a great amount of research dedicated to multiple neurological syndromes (movement disorders, cognitive impairments, epilepsy, brain tumors, etc.). It is in particular well-suited to investigated processes of functional connectivity in the brain, to elucidate the function of cerebral networks.

MEG technology is the safest of all 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 and clinical research, and especially in investigations involving young children (a care giver can attend the subject in the scanning room).

The advantage of sensing magnetic fields – as opposed to the related electrical fields, as with electroencephalography(EEG) – is that they pass through the skull and other head tissues 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 scanner monitorMEG 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).

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.

Read more about MEG brain imaging

We have assembled under the links below the equivalent of 50 book pages, where you can learn more about instrumentation, MEG techniques and applications to clinical and fundamental cognitive neuroscience. Enjoy!
  1. Introduction to functional brain imaging
  2. MEG/EEG Principles and Instrumentation
  3. Scenarios of typical MEG/EEG session
  4. Data preprocessing
  5. Electromagnetic neural source imaging
  6. References