Fig. 1. Time-varying entropy/complexity of the electroencephalographic signal. The sets of  curves corresponding to Higuchi fractal dimension (HFD), Lempel-Ziv complexity (LZC), approximate entropy (ApEn), and spectral entropy (SpEn) are plotted below each other, with corresponding  scales at the left of each panel.  Red , green , and  blue curves correspond to subject groups remi0, remi2, and remi4, respectively. The nine  panels correspond to the nine frequency bands as indicated at the top of each panel. The signal frequency band is shifted from low frequencies toward higher frequencies while moving from the upper left panel toward the lower right panel of the figure. Monotonic behavior of the presented electroencephalographic measures is lost when high frequencies are cut off and/or low frequencies are preserved.