An improved method for localizing electric brain dipoles

An improved method for noninvasive localization of equivalent dipoles in the brain is presented and evaluated. The method has been tested and evaluated on humans in vivo. The head is represented by a three-layer spherical model. The potential on any point on the scalp due to any source is found by a closed formula, which is not based on matrix rotations. The formulas will accept any surface electrode as the reference electrode. The least-squares procedure is based on optimal dipoles, reducing the number of unknowns in the iterations from six to three. The method was evaluated by localizing five implanted dipolar sources in the human sensorimotor cortex. The distances between the locations of the sources as calculated by the method and the actual locations were between 0.4 and 2.0 cm. The sensitivity of the method to uncertainties encountered whenever a real head has to be modeled by a three-layer model has also been assessed.