Computational and Mathematical Methods in Medicine
Volume 8 (2007), Issue 3, Pages 173-189
Original Article

Model-Based Analysis and Optimization of the Mapping of Cortical Sources in the Spontaneous Scalp EEG

1Signal Processing Systems Group, Department of Electrical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
2Department of Clinical Neurophysiology, Epilepsy Center Kempenhaeghe, Heeze, The Netherlands
3Center for Electrophysiological Diagnostics, Vlijmen, The Netherlands
4Laboratory for Clinical and Experimental Neurophysiology (LCEN), Department of Neurology, Reference Centre for Refractory Epilepsy, Ghent University Hospital, Ghent, Belgium

Received 19 March 2007; Revised 13 June 2007; Accepted 20 June 2007

Copyright © 2007 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The mapping of brain sources into the scalp electroencephalogram (EEG) depends on volume conduction properties of the head and on an electrode montage involving a reference. Mathematically, this source mapping (SM) is fully determined by an observation function (OF) matrix. This paper analyses the OF-matrix for a generation model for the desynchronized spontaneous EEG. The model involves a four-shell spherical volume conductor containing dipolar sources that are mutually uncorrelated so as to reflect the desynchronized EEG. The reference is optimized in order to minimize the impact in the SM of the sources located distant from the electrodes. The resulting reference is called the localized reference (LR). The OF-matrix is analyzed in terms of the relative power contribution of the sources and the cross-channel correlation coefficient for five existing references as well as for the LR. It is found that the Hjorth Laplacian reference is a fair approximation of the LR, and thus is close to optimum for practical intents and purposes. The other references have a significantly poorer performance. Furthermore, the OF-matrix is analyzed for limits to the spatial resolution for the EEG. These are estimated to be around 2 cm.