Figure 2. Oscillatory signatures of NREM sleep.

(A) Uncorrected EEG power spectra (mean ± standard error of the mean [SEM]) during NREM (NREM2 and NREM3) sleep at Cz during childhood (blue) and adolescence (red). Grey overlays indicate significant differences (cluster-corrected). Note the overall power decrease from childhood to adolescence. (B) Z-normalized EEG power spectra. Same conventions as in (A). Significant differences indicate a change in the fractal component of power spectra (0.3–8.4 Hz) and a spindle frequency peak shift (10.6–14.8 Hz) from childhood to adolescence. (C) Extracted 1/f fractal component. Same conventions as in (A). Decrease of the fractal component (0.3–10.8 Hz) from childhood to adolescence. (D) Oscillatory residual of the NREM power spectra obtained by subtracting the fractal component (C) from the z-normalized power spectrum (B). Oscillatory residual shows clear dissociable peaks in the SO and sleep spindle frequency range (dashed boxes) during both time points, indicating true oscillatory activity. (E) Spindle amplitude development. Spindle amplitude (exemplary depiction at Cz, left, mean ± SEM) as extracted from the oscillatory residuals (D) indicating an increase in 1/f corrected amplitude within a centro-partial cluster (right) from childhood to adolescence. Grey dots represent individual values. Asterisks denote cluster-corrected two-sided p<0.05. T-scores are transformed to z-scores to indicate the difference between childhood and adolescence. (F) Spindle frequency peak development. Spindle frequency peak (mean ± SEM) as extracted from the oscillatory residual (D). Same conventions as in (E). Spindle peak frequency increases at all electrodes from childhood to adolescence.

Figure 2—figure supplement 1. SO feature development and correlations between oscillatory features and behavior.

(A) SO amplitude development. SO amplitude (exemplary depiction at Cz, lower panel, mean ± SEM) as extracted from the oscillatory residual (peak <2 Hz, Figure 2D) indicating a decrease in 1/f corrected amplitude within a central cluster (top panel) from childhood to adolescence. Grey dots represent individual values. Asterisks denote cluster-corrected two-sided p<0.05. T-scores are transformed to z-scores to indicate the difference between childhood and adolescence. (B) SO frequency peak development. Spindle frequency peak (mean ± SEM) as extracted from the oscillatory residual (Figure 2D). Same conventions as in (A). SO peak frequency decreases at all sensors but Fz from childhood to adolescence. (C) Cluster-corrected correlations between developmental change in sleep spindle amplitude (left) and peak frequency (right) with recall performance improvement in the delayed recall from childhood to adolescence. No significant clusters emerged. (D) Same convention as in (C) but for SO amplitude (left) and peak frequency (right). No significant clusters emerged. (E) To extract theta oscillatory features, we detected the peaks in the oscillatory residual (Figure 2D) during NREM sleep in theta frequency range (4–7 Hz) and extracted the maximum (theta amplitude) and corresponding frequency (peak frequency). Cluster-corrected correlations between developmental change in theta amplitude (left) and peak frequency (right) with recall performance improvement in the delayed recall from childhood to adolescence. No significant clusters emerged.

Figure 2—figure supplement 2. Individual oscillatory residuals and spindle frequency gradient.

(A) Exemplary NREM oscillatory residual during childhood (blue) and adolescence (red) for 10 subjects at Fz and Cz. Note, most subjects did not express two clear spindle frequency peaks (Fz: 16/66 nights; Cz 8/66 nights). (B) Topographical plots of spindle peak frequency during childhood (left) and adolescence (right) during NREM sleep showing the typical antero-posterior spindle frequency gradient with slower frontal and fast centro-parietal spindles. Note the change in the colorbar scaling due to the overall spindle frequency increase (Figure 2F).