1. A method of estimating cerebral sources of electrical activity from a set of EEG channels comprising the steps of: obtaining M channels of measured EEG signal data and N-M channels of synthetic EEG signal data, where M<N; creating sets of N-M channels of synthetic EEG signal data; calculating an inverse solution from a combination of said sets of N-M channels of EEG signal data and said M channels of EEG signal data.