- Magnetoencephalography (MEG): This test records magnetic field changes produced by brain activity. During the test, the subjects are seated in the MEG recording room and a cone containing magnetic field detectors is lowered onto their head. Electrodes (small metal disks) are placed on both sides of the face near the jaw. The recording may be made while the subject receives small currents from the electrodes on the jaw. Subjects may be asked a few questions about what they felt during the procedure.