MEG  [ back to Neuroimaging ]
MEG or magneto-encephalography is a new technique which detects, measures and maps the extremely tiny magnetic fields generated by the flow of micro-electric current in brain cells which are actively firing. These fields are one-billion times weaker than the earth’s, but can be accurately measured using an exquisitely sensitive magnetic energy scanner called SQUID (superconducting quantum interference device). From SQUID measurements of local magnetic field strengths through the 3 dimensions of the patient’s brain, the computer can back calculate the strength of the micro-electric current which generated those miniature magnetic fields and locate them within the space occupied by the brain in the form of a neural map of brain activity. Such a map is important not only for what it shows (activity) but for what it does not show (lack of activity). In this way one can presumably establish that small areas of the brain which should be actively firing in response to a given mental stimulus (and generating tiny but measurable magnetic fields as a consequence of firing) are silent and therefore damaged or dead.