Magnetoencephalography (MEG) is a non-invasive neuroimaging technique. During cognitive processes, the simultaneous activation of a large number of cerebral neurons (pyramidal cells) gives rise to a dendrite electric current. These synchronized currents induce tiny magnetic fields that can be measured outside the skull. The magnitude of this magnetic field is typically within a femtotesla range. It is a thousand times weaker than the magnetic field generated by electric devices or moving magnetic objects and about one billion times smaller than the Earth’s static magnetic field. Therefore, measurement of the brain’s magnetic fields requires extremely sensitive sensors and an optimal shielding provided by the magnetically shielded room (MSR). The MEG at CIPP is equipped with 306 of these sensitive sensors and a state-of-the-art MSR. MEG allows inside into the dynamic interactions between cortical modules during perceptual, cognitive, motor, motivational and emotional brain processes.
Advantages / disadvantages compared to other methods
The signals measured by MEG are very similar to those measured by EEG. Unlike EEG, MEG is a reference-free method characterized by higher source localization (where in the brain) and source reconstruction (what is the temporal profile at a given location) accuracy. Participant’s preparation is typically less than 5 minutes and there is no application of abrasive or conductive gel prior to the MEG acquisition unless simultaneous EEG is performed. Combined with MRI, MEG provides the best of both worlds: good spatial resolution in the millimeter range and temporal resolution in millisecond range. However, MEG’s sensitivity to cortical currents depends on their location and orientation. MEG signals are typically stronger on sulcus walls as compared to gyral crowns. Moreover, sources located deeper in the brain are challenging to image and require a reasonable increase in signal-to-noise ration to be detected by MEG. In contrast, EEG signals do not depend on the orientation and location of the underlying sources.
Risks / Limitations
There are no known risks associated with MEG acquisition.
Bankim Subhash Chander, PhD., Core Facility ZIPP
Zentralinstitut für Seelische Gesundheit (ZI) - https://www.zi-mannheim.de