EEG dipole tracing

Mathematical processes are described for constructing the SSB head model and estimating the equivalent current dipoles from scalp potentials, which is called the Dipole Tracing (DT) method. The SSB head model is a 3-compartment head model in which uniform electric conductors replace scalp, skull and brain which have different electric conductivities. Accuracy of the estimated dipole locations is calculated in the presence of noise. The electric conductivities of the three shells differ from subject to subject, and conductivity ratios that optimize the SSB head model are determined experimentally by passing electric currents in the head and analyzing the resulting surface potentials. This technique allows more accuracy of the estimated dipole location. Accuracy of the SSB/DT method in a real head was obtained with intracranial subdural electrodes implanted in epileptic patient brains. Finally the physiological meaning of the goodness-of-fit of the dipole approximation of electric activity of the brain cortex is discussed. It is found by computer simulation that it is tightly connected with the degree of impairment of the cortex