Dipole source localization of interictal epileptiform activity in temporallobe epilepsy with medial temporal lesion

Dipole sources of interictal epileptiform activities recorded by convention al electroencephalogram (EEG) were estimated using the dipole tracing metho d. Four cases of temporal lobe epilepsy with medial temporal lesions were s tudied. Two patients with hippocampal sclerosis, one patient with granulati on in the hippocampus and one patient with cavernous angioma were involved in the study. Interictal epileptiform activities were classified into two p atterns according to the topography of spikes. They were widespread spikes over the parasagittal electrodes (parasagittal spikes) and restricted spike s at the temporal electrodes (temporal spikes). Dipole sources of parasagit tal spikes were localized in the medio-basal temporal lobe with vertically orientated vector moment. Dipole sources of temporal spikes were localized in the medio-basal temporal lobe with horizontally orientated vector moment . Locations of dipoles and directions of vector moments were consistent wit h topography and polarity of spikes. The difference in the two patterns of interictal epileptiform activities was derived from the difference in the d irection of the vector moment of dipole sources. There was no difference in the location of dipole sources. Both the dipole sources and the lesions we re localized in the same medio-basal temporal lobe. Dipole tracing was very useful in localizing the dipole sources of interictal epileptiform activit ies and in understanding the neurophysiological background.