Figure 1

Representative double-plotted actograms of wheel-running activity in mice from Experiment #1 exposed to T24 LDLD, T30 LDLD and DD where the T24 and T30 phases included dim scotophase illumination (DSI) (a, LD^im7:5/LD^im10:5) or complete darkness (b, LD^ark7:5/LD^ark10:5). The actogram shown in C is not representative of the group, but illustrates anomalous bifurcation in dark nights (LD^ark7:5/LD^ark10:5) resembling the pattern shown in a. The same data from T30 are double-plotted modulo-24 h in (a–c) and again modulo-30 h in (d–f). Shading reflects times of relative darkness (dark shading is complete darkness; lighter shading is DSI). Shading in T30 LDLD is omitted in actograms plotted modulo-24 h (a–c) to aid in visualization of the underlying activity pattern, but shown for modulo-30 h plots (d–f). Dashed white lines illustrate best-fit lines to determine free-running period and projected activity onset phase in DD. In b, dark line shows best-fit line through free-running activity onsets in LDLD. Lomb-Scargle periodograms (g,h) for the final 14 complete LDLD cycles in T24 (Phase 1) and T30 (Phase 2) are shown for the same three animals shown above.