A method for combining MEG and EEG to determine the sources.

A three-step method is presented which combines an MEG and EEG map over the head to solve the inverse problem (to determine the sources). This method uses the feature that the MEG does not see a radial source, but only a tangential source, while the EEG sees both. A first test is also made of the method, using computer simulation, and the results presented. The purpose of the test is to see if the method is valid with noisy MEG and EEG data, and when some modelling errors are present; a single dipole source was used in a spherical head. It was found that the method works well when the RMS noise at each map location is 5% of the maximum MEG and EEG (readily attained in practice), but breaks down when the noise is 10% (quite noisy data). The modelling errors involved grid size, head radius and distance to the MEG coil, and were studied only through the first step of the method; with errors in a reasonable range, this limited test again worked well.