LOCATION OF ELECTRIC-CURRENT SOURCES IN THE HUMAN BRAIN ESTIMATED BY THE DIPOLE TRACING METHOD OF THE SCALP-SKULL-BRAIN (SSB) HEAD MODEL

Using a realistic, 3-shell head model including the scalp (S), skull ( S) and brain (B) with conductivity ratios of 1:1/80:1, respectively, t he electrical activity in the human brain recorded by conventional ele ctroencephalography was approximated by 1 or 2 equivalent current dipo les. The dipole locations and vector moments were estimated by minimiz ing the squared difference between the potentials actually recorded fr om the scalp and those theoretically calculated from the equivalent di poles. The validity of this dipole tracing method (the DT of the SSB h ead model) was tested in patients with focal epileptic seizures underg oing presurgical evaluation with intracranial subdural strip electrode s. Weak currents were passed through 1 or 2 pairs of subdural electrod es to create artificial dipoles. The dipole estimations correctly dist inguished between single and double generator sources, but there were certain dislocations of the calculated dipoles. The average error of d islocation was found to be 8.5 mm for the 1-dipole model. That for the 2-dipole model was 6 mm for one of the components and 18 mm for the o ther. It was concluded that the DT method of the SSB head model can be a valuable clinical tool in 3-dimensional localization of focal epile ptic discharges in the human brain.