The electrophysiological basis of epileptiform magnetic fields in neocortex.

Electrical measurements of epileptiform cellular currents in a penicillin model of focal epilepsy were directly compared to the extracranial magnetic fields these currents produce. Our data support the hypothesis that epileptiform magnetic fields result from intradendritic currents oriented perpendicular to the cortical surface. Furthermore, magnetic fields could be detected from epileptic foci smaller than 3 mm2. This work provides an empirical foundation for physical models with which to interpret noninvasive neuromagnetic recordings of epileptic discharge in human focal seizure disorders.