Abstract
The goal of this study was to investigate the influence of the brain-to-skull conductivity ratio (BSCR) on EEG source localization accuracy. In this study, we evaluated four BSCRs: 15, 20, 25, and 80, which were mainly discussed according to the literature. The scalp EEG signals were generated by BSCR-related forward computation for each cortical dipole source. Then, for each scalp EEG measurement, the source reconstruction was performed to identify the estimated dipole sources by the actual BSCR and the misspecified BSCRs. The estimated dipole sources were compared with the simulated dipole sources to evaluate EEG source localization accuracy. In the case of considering noise-free EEG measurements, the mean localization errors were approximately equal to zero when using actual BSCR. The misspecified BSCRs resulted in substantial localization errors which ranged from 2 to 16 mm. When considering noise-contaminated EEG measurements, the mean localization errors ranged from 8 to 18 mm despite the BSCRs used in the inverse calculation. The present results suggest that the localization accuracy is sensitive to the BSCR in EEG source reconstruction, and the source activity can be accurately localized when the actual BSCR and the EEG scalp signals with high signal-to-noise ratio (SNR) are used.
Highlights
The electroencephalogram (EEG) measures scalp electrical potential which is propagated from neuronal source activity within the brain through the head volume conductor
We focused on elaborating the effect of different brain-to-skull conductivity ratio (BSCR) on EEG source localization accuracy by using huge amounts of dipole sources on the cortical surface and a 3-dimensional (3D) head model based on realistically shaped head volume conductor
When the BSCRs used in the inverse calculation were 15, 20, and 25, the source localization errors showed the same trends that the localization errors decreased as the depth of dipole sources increased
Summary
The electroencephalogram (EEG) measures scalp electrical potential which is propagated from neuronal source activity within the brain through the head volume conductor. The EEG signals can be recorded on the scalp of human head via appropriate electrodes, and they provide important information about brain electrical activity. In the majority of the EEG source localization methods, a piecewise homogenous head model is used to represent the physical properties of the human head volume conductor. This model usually consists of three compartments (brain, skull and scalp), which are segmented from MR images. The conductivities of different tissues are assigned to each compartment [7] These conductivity values play a critical role in determining the relationship between the recorded scalp potentials and neuronal currents within the brain. It is very important to specify the brain-to-skull conductivity ratio (BSCR) in EEG source localization
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