MEG MEASUREMENT IN EPILEPSY

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Because of a number of unique properties of neuromagnetic fields, magnetoencephalography (MEG) promises to be a valuable tool for the non-invasive study of epileptic phenomena in man and animals. Neuromagnetic measures have recently been applied to the practical localization of epileptic foci in the three dimensional cranial space of patients with focal seizure disorders. Yet, the capacity of MEG to measure intracellular currents, and to record both rapid and extremely slow changes of these currents, make MEG not just a practical localization tool but a means of noninvasively studying the cellular mechanisms of epilepsy. To realize this potential, we propose to study penicillin epilepsy in the rat. Three initial experiments are proposed to establish an empirical foundation for the neurogenesis of neuromagnetic fields in epilepsy. In these studies, the relationship between magnetic field strength and the size of the epileptic focus, the orientation of magnetic fields and cells within the focus, and possible contributions of secondary sources will be examined. The fourth experiment examines the relationship between magnetic field patterns and known intracellular currents produced by direct cortical stimulation, for comparison to the fields of penicillin epilepsy. The remaining experiments draw upon this empirical data to explore the intracellular currents of interictal spiking, rapid seizure spiking, slow ictal field shifts, and possible interictal standing fields. This work will introduce an entirely new area of biomagnetism, animal magnetometry. The empirical foundation for the neurogenesis of neuromagnetic fields established in this work will substantiate the interpretation of all studies in the growing field of neuromagnetism. Exploratory studies in the magnetic fields of penicillin epilepsy will serve as a necessary starting point for future neuromagnetic studies of the cellular mechanisms of epilepsy. Finally, the investigation of slow and standing fields in the rat may introduce a powerful new method of localizing and studying seizure foci in patients with focal seizure disorders.