Magnetoencephalography (MEG) Core Facility

Magnetoencephalography Core (MEG)  is a non-invasive procedure similar to electroencephalography (EEG) in terms of basic principles and analysis. However, while EEG measures the electric fields generated by the brain, MEG measures magnetic fields. An MEG exam consists of sitting in a chair or lying on a bed while your head is inside a helmet shaped device which contains magnetic field sensors. These superconducting quantum interference device (SQUID) sensors passively detect weak magnetic fields (10^-14 Tesla) outside the head produced by brain activity. The 275 SQUID sensors are uniformly distributed, in a grid, over the inner surface of the helmet that covers the entire head. Head position within the MEG system will be determined before and after the session by digitizing the position of three indicator coils that are attached to the pre-auricular and the nasion fiducial points. The positions of these coils define the coordinate system for the signals. Digital photographs of the fiducial points are also taken to localize the same points on the participant’s anatomical MRI scan.

A key advantage of MEG over EEG is the ability to better localize the source of signals accurately in the brain. In addition, compared to EEG systems, MEG systems allow higher spatial sampling resolution. Under favorable conditions, spatial localization of current sources with whole head MEG is on the order of 2-3 mm at a temporal resolution better than 1 ms. Thus MEG is an important tool in the search to better understanding of the functioning of the brain.