Fig. 2

Power spectral analysis and comparison of group-level spectrograms. A Group-level median frontal spectrogram showing prominent power in the slow wave and alpha band ranges. B Group-level median frontal spectrogram showing a distinct decrease in power in the α frequency band. White solid lines in A and B represent SEF95. C Medians of 21 superimposed power spectra from 5 min before Dex injection (blue line) versus 10 min after (red line). From the pre- to the post-injection time points, the α peak showed a power reduction and slight left-shifting of frequency, while the power of slow waves increased sharply. D Median spectral power difference curve across the two periods at each frequency; shading represents 95% CI range. Approximately 10 min after Dex injection, EEG power was greater in the range of 0~4.8 Hz and lesser in the range of 6.8~40 Hz. The horizontal lines above the x-axis in C and D represent the frequency range at which the power differed significantly across evaluation time periods. E Comparison of mean α peaks (± SDs) before versus after Dex injection for 21 cases; ***p < 0.001, paired t test. F Comparison of frequencies of α peaks plotted as box plots. Horizontal lines in the boxes indicate the median values, the box top/bottom indicates 25% and 75% quartiles, and whiskers indicate the minimum and maximum values for the 21 cases. The means are shown with the end points of the solid diagonal line, the shading around which reflects standard errors of the means; ****p < 0.0001, paired t test