Figure 1.

Representative single-plotted wheel-running actograms of individual hamsters exposed to LDLD cycles incrementally lengthening or shortening from T=24 h to T=30 h (A) or T=18 h (B), respectively. In both cases, the length of each of the two dark phases was fixed at 4 h. To align the entire actogram vertically and highlight the changes in entrainment with respect to dark onset, the representation of intervening light phases is systematically distorted. White areas represent light while blue areas are space holders that represent no time but allow alignment of the scotophases throughout the transition from T24 to T30 or T18, respectively. In all LDLD cycles in this study scotophases (D) were dimly illuminated (561 nm LEDs provided constant dim illumination of < 0.1 lux). The actograms illustrate the robust control of activity throughout the experiment in both groups, the more variable pattern of activity onsets in T18 versus T30 and the absence of apparent free-running rhythmicity.