Spatial filtering or beamforming approaches have recently been developed for the field of electro- (EEG) and magnetoencephalography (MEG) source analysis and opened up new applications within various fields of neuroscience that could previously not be explored by traditional techniques relying on averaged evoked responses. While the number of beamformer applications thus increases fast-paced, fundamental methodological considerations, especially the dependence of beamformer performance on leadfield accuracy, is still quite unclear. In this paper, we present a systematic study on the influence of improper volume conductor modeling on the source reconstruction performance of an EEG-data based synthetic aperture magnetometry (SAM) beamforming approach. A finite element model of a human head is derived from multimodal MR images and serves as a realistic volume conductor model. By means of a theoretical analysis followed by a series of computer simulations deep insight is gained into beamformer performance with respect to reconstruction errors in peak location, peak amplitude and peak width resulting from geometry and anisotropy volume conductor misspecifications, sensor noise and insufficient sensor coverage. We conclude that depending on source position, sensor coverage, and accuracy of the volume conductor model localization errors up to several centimeters must be expected. The spatial distribution of peak amplitude and width, important for the assessment of the local relevance of beamformer results, strongly depends on the noise level in the case of inaccurate volume conductor models and becomes nearly unpredictable if the signal-tonoise ratio is high.

@TechReport{SSJBW09,
  author       = {Steinstraeter, O. and Sillekens, S. and Junghoefer, M. and Burger, M. and Wolters, C.},
  title        = {Sensitivity of beamformer source analysis to deficiencies in forward modeling},
  institution  = {WWU Muenster},
  year         = {2009},
  url          = \{/2009/SSJBW09},
}