Spatial resolution of neuronal generators based on EEG and MEG measurements.

A unique solution to the electromagnetic inverse problem of neurophysiology does not exist due to the fact that scalp measurements of electric potential differences and of magnetic field components contain only partial information about the sources. Three different information functionals are introduced in this paper and are based on the following intuitive ideas, where the amount of information is: (1) Directly related to the amount of change in the measurements due to a very small change in the source; (2) Directly related to the angle between two sets of measurements corresponding to two different sources; and (3) Inversely related to the distance between the minimum norm inverse solution and the actual source. These definitions are used for comparing the source resolution of EEG and MEG in an inhomogeneous spherical head model. The main conclusion is that in many realistic situations electric measurements are more informative than magnetic measurements.