Figure 9.

A, top, Correlation between the cascade magnitude and the BOLD-CA amplitude (Fig. 4B,C, blue and green lines) for different time lags in several EEG/fMRI trials extracted from a Human cohort of resting subjects. Negative lag is associated with a shift backward of the BOLD signal. A, bottom, The cross-correlation averaged across trials shows a clear trend (blue line). The peak of correlation at lag –2 sampling points (1 pt = 1.94 s), as well as the rapid fall for positive lags, confirms that the EEG precedes the BOLD activity by few seconds. The same profile is evaluated by comparing the largest cascades with the BOLD-CA signals extracted from 1000 time-shuffled (example in green), 1000 phase-randomized (cross-spectrum preserved, example in orange), and 1000 phase-randomized (cross-spectrum not preserved, example in red) BOLD surrogates for every subject (see Extended Data Fig. 9-1A,B for surrogate properties). B, The distribution of the mean, maximum, and variance of the cross-correlations for each surrogate model is displayed and compared with the empiric values. In particular, the variance plot shows a clear significance of the results (single subject results in Extended Data Fig. 9-1C).