ON THE SENSITIVITY OF THE HUMAN BRAIN TO MAGNETIC-FIELDS - EVOCATION OF EPILEPTIFORM ACTIVITY

Evocation of epileptiform activity by DC magnetic fields of between 0. 9 and 1.8 millitesla (mT) has been demonstrated in 6 epileptic patient s undergoing presurgical evaluation. The activity was monitored by ele ctroencephalography (EEG) recording from both electrodes attached to t he scalp as well as from intracranial electrodes inserted via the fora men ovale. Epileptiform activity evoked by the magnetic field applicat ion was distinguished from background levels by comparing the number o f epileptiform discharges in the 10-s intervals before and after field applications. In nearly all cases, a delay of up to several seconds w as observed between the application of the magnetic field and the onse t of epileptiform firing. Removal of the field also appeared to cause firing in some instances, but this has not yet been investigated syste matically. In all 6 patients, subsequent seizures confirmed that the e pileptiform activity monitored during the experiments was originating from the primary epileptogenic zones of the patients.