Several functional imaging techniques are now available which provide the possibility to look non-invasively inside the brain in vivo and to study human brain function. Magnetoencephalography is one such functional brain imaging technique, which is truly non-invasive and allows the localization of the electrical activity of nerve cells within the brain with a few mm accuracy and fast time resolution (~1 msec).

During the MEG recording, the subject is lying on a bed and the MEG system is placed close to the subject's head. The MEG system is located in a magnetically shielded room and consists of a dewar filled with liquid helium, containing detection coils and superconducting electronics.

The magnetic field generated by intracellular currents from an individual neuron is extremely small, too small to be detected outside the head. In fact, several thousand synchronously active neurons are needed to generate the field measured by the MEG. The magnetic fields being measured from the brain are in the range of 50-1000 femtotelsa (fT), which is an extremely weak signal and is about one billion times smaller than the earth's magnetic field. The MEG technique has very sophisticated instrumentation sensitive enough to detect these weak signals, while simultaneously discriminating against interference from strong background noise.