The estimation of time varying dipoles on the basis of evoked potentials

When a stimulus is presented to a subject, different cortical areas are activated simultaneously. These cortical sources are the generators of evoked potentials. The geometry parameters and the amplitude time course of each source can be estimated on the basis of EP data and the appropriate mathematical model. In the present paper, a model is proposed which describes EPs as the result of a set of stagnant dipoles, with time varying amplitude. It is shown how the parameter estimation problem can be solved efficiently. The method automatically solves the problem of separating overlapping components. A lower limit for the residual is derived, which can be used to determine the minimum number of sources required to describe observed responses adequately.