The most fundamental problem of MEG or EEG localization is that the inverse problem is ill-posed. Both for the MEG and for the EEG source configurations exist that do not contribute to the recorded potentials or magnetic field gradients. It follows that there is not a unique source configuration for each recording. What the character of silent sources is depends on the symmetries present in the volume conductor model. It can for instance be shown that when the volume conductor and current sources have rotation symmetry the magnetic field outside the conductor is zero even in the case of anisotropia (de Munck and van Dijk 1991). To solve the problem of ill-posedness there is only one way out: put in a priori knowledge about possible solutions. For in-

EEG localization, the most fundamental problem is that there is not a unique source configuration for each recording, and the solution is to put in a priori knowledge about possible solutions.

Equivalent dipole source localization of EEG and evoked potentials: Sources of errors or sources with confidence?

Key Takeaway: EEG localization, the most fundamental problem is that there is not a unique source configuration for each recording, and the solution is to put in a priori knowledge about possible solutions.