Anatomically and functionally constrained MEG/EEG source estimates:

Theoretical background and practical implementation in the MNE

software

Matti S. Hämäläinen

Independently, electromagnetic and hemodynamic measurements of brain activity offer compromises
between spatial and temporal resolution. Functional Magnetic Resonance Imaging (fMRI) is temporally
limited by the slow time course of the hemodynamic response, but can provide a spatial sampling on a
millimeter scale. Electroencephalography (EEG) and magnetoencephalography (MEG) in turn provide a
temporal resolution of milliseconds, but the localization of sources is more complicated because of the ill-
posed electromagnetic inverse problem.
This presentation will cover the theoretical and technical background of MEG/EEG source estimation
with emphasis on the weighted l2-norm solutions and on the use of anatomical and fMRI data to constrain
the solutions. In addition, our novel sparse but temporally smooth l1l2-norm approach as well as our
recently proposed fMRI-Informed Regional EEG/MEG source Estimation (FIRE) will be discussed. The
region-based approach makes FIRE computationally efficient and comparisons with several joint fMRI-
EEG/MEG algorithms demonstrate the robustness of FIRE in the presence of sources silent to either
fMRI or EEG/MEG measurements. The talk will conclude with an overview and demonstrations of the
capabilities of the MNE software.