Neuromagnetic localization of epileptiform spike activity in the human brain.

Local paroxysmal discharges of epileptic tissue within the human brain, which may be electrically recorded as voltage spikes in the electroencephalogram, also generate extracranial magnetic fields. These fields were assessed by means of recently developed neuromagnetometric techniques. Surface measurements of magnetic spike field strength in the region of the focus appear sufficient to establish the location, depth, orientation, and polarity of currents underlying the paroxysmal discharge.