Estimation of neural architecture in human brain by means of the dipole tracing method

The electric source locations of interictal spikes recorded with depth electrodes were estimated by the dipole tracing (DT) method. Three-dimensional coordinates of the active surfaces of the depth electrodes and head geometry of the patient were measured from frontal and sagittal X-ray images and by a special device, respectively. The estimated dipole locations were superimposed on MR images of the patients. The dipole locations estimated in the hippocampal or parahippocampal regions successively moved in a small limited region during the interictal spike's peak. It was suggested that an interictal spike is composed of summated equivalent dipoles generated by hypersynchronization of a cluster of neurons, and that the timing of such hyperexcitation is more or less delayed because of electrical propagation along neuronal clusters which might be separated by sclerotic tissues.