Repeated sleep restriction in rats leads to homeostatic and allostatic responses during recovery sleep

Kim et al. 10.1073/pnas.0610351104.

Supporting Information

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SI Figure 4
SI Table 2
SI Figure 5

Fig. 4. Schematic diagram of experimental design. A 24-h baseline (BL) sleep-wake recording was collected beginning 4 h after light onset (zeitgeber time 4, ZT 4). Over the next 5 consecutive days, animals were sleep-deprived for 20 h (SD1-SD5) followed by a restricted 4-h sleep opportunity (SR1-SR5). Thereafter, animals had a 3-day ad libitum sleep recovery (R1-R3) opportunity. The protocol was designed so that the 4-h sleep opportunity blocks occurred during the first 4 h of the light phase (ZT0-4). The 12:12 light:dark cycle is indicated at the bottom (open bar = light phase, dark bar = dark phase).

Fig. 5. Cumulative sleep loss and gain across the sleep deprivation/restriction and recovery periods. The amount of sleep during the baseline (BL) period was used to determine the amount of sleep deprivation that occurred during the 20-h (ZT4-24) time blocks on SD1-SD5. The amount of sleep lost was accumulated over the 5 days and plotted as net sleep loss. The amount of sleep regained over BL levels during the restricted 4-h (ZT0-4) sleep opportunities was also summed over SD1-SD5 and plotted as net sleep gain. It is clear that despite a large amount of accumulated sleep loss, animals only regained a small portion of their potential net recovery during the 4-h sleep opportunities. These same calculations were continued across the 3 days of ad libitum recovery sleep opportunity (R1-R3). The data are presented in hours (±SEM) for total sleep time.

Table 2. Delta energy during ZT4-24 time block

Cumulative energy in the EEG delta (0.5-4.0 Hz) frequency range (i.e., summed delta power over all epochs) was determined during the 20-hr time blocks (ZT4-24) for baseline (BL), sleep deprivation (SD1-SD5), and recovery (R1-R3) days. Delta energy was used because it provides a measurement of the total delta activity achieved during the 20-h time block regardless of (i) whether any NREM sleep, as achieved and (ii) the number of mixed wake-NREM epochs. The use of delta energy eliminates the potential confound of overestimating wake delta power and underestimating NREM delta power because of the mixed wake-NREM epochs (i.e. micro-sleeps) that frequently occurred in the sleep deprivation wheel. The total energy was divided by the total number of epochs included in the analysis (delta energy per 10-sec epoch) in order to adjust for epochs that were eliminated from analysis because they contained EEG artifact. These data indicate that delta energy during the 20-h time blocks was similar across BL, SD, and R days (F_(8,56) = 0.70, P = 0.68) and that despite losing a large amount of NREM sleep in the wheel, animals did not compensate by increasing overall delta energy during the 20-h time interval.

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