Figure 5.

Effects of sleep deprivation on NREM sleep, EEG delta power, and sleep-onset latency as a function of time of day. (A) Mean (± SEM) time course of EEG delta power during NREM sleep (triangles; % of the last 4 h of the baseline light periods), simulated values of “Process S” (lines; right y-axis), and time spent in NREM sleep (circles; min/ recording h; left y-axis) during 48-h baseline (gray symbols and lines) and during and after four 6-h sleep deprivations (SDep) starting either at 48 h (ZT0: orange), at 54 h (ZT6: yellow), at 60 h (ZT12: green), or at 66 h (ZT18, blue) after the start of the recording. Gray areas delineate the dark periods. Note that for baseline, all 4 experimental groups were pooled (n = 33), rendering SEM smaller than symbol size. (B) Loss of time spent in NREM sleep varied among the 4 sleep deprivations. Vertical bars represent mean (± SEM) difference between NREM sleep during the sleep deprivation and during the corresponding 6-h interval during baseline and thus reflect mainly the distribution of NREM sleep during baseline. Asterisks mark significant differences among sleep deprivations (post hoc Tukey; P < 0.05; ZT0 = ZT6 > ZT18 > ZT12). Color coding for sleep deprivation timing as in panel A. ZT times indicated refer to the start of the sleep deprivations. (C) Sleep onset latency, calculated from the end of the sleep deprivation to the first consolidated NREM sleep bout, importantly varied among sleep deprivations. See panel B for details. (D) Differences between empirical and simulated levels of EEG delta power calculated for the first 20 min of NREM sleep after sleep deprivation. Asterisk indicates significant differences between observed and predicted values (post hoc, paired t-tests; P < 0.05). See panel B for details.