Figure 2.

Resynchronization of sleep–wake states and SWDs to an 8-h phase shift in the photoperiod. WAG/Rij rats (n = 8) were kept in baseline, 12:12 light–dark cycle. Next, the timing of the light phase was once delayed for 8 h followed by again a 12:12 light–dark cycle. The process of adjustment to the new photoperiod was observed during 10 postshift days. The speed of resynchronization was found rhythm-specific; however, some rhythms, such as active wakefulness and deep slow-wave sleep, and SWDs and light slow-wave sleep resynchronized together, which may indicate that a common circadian mechanism is responsible for those pairs of rhythms. Total duration of sleep–wake states (in minutes) and the number of SWDs during particular postshift days were plotted with respect to the baseline. The dark phase of the 12:12 light–dark cycle is marked by gray rectangles. ^*p < 0.05, acrophase of the baseline vs. acrophase on the postshift day; #p < 0.05, nadir of the baseline vs. nadir of the postshift day, analysis of variance for repeated measures, Bonferroni post hoc test or Friedman analysis of variance, and Dunn multiple comparison post hoc test (122 with permission from Elsevier).