Figure 13.

Values of connectivity among the ROIs estimated with the spectral Granger causality, with reference to the network in Figure 2A but with the input to ROIα increased from 200 to 400. The values are plotted as a function of frequency (note the use of different y-axes to emphasize the different cases). From the comparison of these panels with those in Figure 11 emerges that: the α rhythm transmitted from ROIα to the other regions becomes almost sinusoidal (high and sharp spectra (d–f)); the rhythm exchange between ROIβ and ROIγ (a) and between ROIθ and ROIγ (c) are significantly altered, with the presence of components in the α range; finally, spurious connections appear between ROIβ and ROIθ (b), both in the β and α ranges. Comparing this figure with the corresponding bottom panel in Figure 10, the spectral Granger causality provides similar information as the temporal Granger causality, but with emphasis on the frequency bands.