6 Methods for Functional Connectivity Analysis
135
Fig. 6.3 Examples of spurious connectivity (PLV) due to the volume conduction. a Distributions
of phase differences between two EEG channels in gamma band (30–50 Hz), solid lines denote the
phase difference between two channels at a single temporal point, the length of the black arrow
corresponds to the magnitude of average PLV. b Correlation between PLV and inter-electrode
distance in gamma band. c Correlation between PLV and spectral power in gamma band
the potential problem of the FC analysis using surface EEG, at least they should be
checked to verify whether the conclusions are made by spurious effects of volume
conduction.
6.4.2 Spatial Filtering
Surface Laplacian is a method to estimate the amount of current source density (CSD)
at the scalp, and behaves as a spatial highpass filter [43]. The potential distribution
of EEGs on the scalp usually have low spatial frequency component due to volume
conduction. When the surface Laplacian is properly used, the spurious low spatial
frequency components may be reduced. As a result, its confounding effect on FC
may be eliminated as well (For review of the algorithm of surface Laplacian, see [28,
43]).
135
Fig. 6.3 Examples of spurious connectivity (PLV) due to the volume conduction. a Distributions
of phase differences between two EEG channels in gamma band (30–50 Hz), solid lines denote the
phase difference between two channels at a single temporal point, the length of the black arrow
corresponds to the magnitude of average PLV. b Correlation between PLV and inter-electrode
distance in gamma band. c Correlation between PLV and spectral power in gamma band
the potential problem of the FC analysis using surface EEG, at least they should be
checked to verify whether the conclusions are made by spurious effects of volume
conduction.
6.4.2 Spatial Filtering
Surface Laplacian is a method to estimate the amount of current source density (CSD)
at the scalp, and behaves as a spatial highpass filter [43]. The potential distribution
of EEGs on the scalp usually have low spatial frequency component due to volume
conduction. When the surface Laplacian is properly used, the spurious low spatial
frequency components may be reduced. As a result, its confounding effect on FC
may be eliminated as well (For review of the algorithm of surface Laplacian, see [28,
43]).