Figure 2.

Id4−/− mice show a reduction in the magnitude of phase delays in response to a 10-h extension of the light phase. (a) Locomotor activity records of wild-type (Id4+/+) and Id4−/− mice exposed to a 10-h extension of the light phase of the light/dark (LD) cycle. Actograms are shown in double-plotted format with each horizontal line representing a 48-h period, and the second 24-h period plotted to the right and below the first. Vertical bars represent periods of wheel-running activity. Mice were exposed to 10 h of prolonged light exposure on day 1 and transferred to constant darkness (DD) for the remainder of the experiment. The line above DD on the right indicates the transition from LD to DD. The timing of the LD cycles is indicated by the white/black bars above the records. The arrow on the left indicates the actual day of treatment (Day 1). A line is fitted to the phase of activity onset for several days before and after the transfer to DD. (b) Mean ± SEM magnitude of the phase shifts produced by light treatment. Extrapolated activity onsets of the first day following the 10-h light treatment was used to determine the size of resultant phase delays. Wild type (WT; white), n = 19; Id4−/− (orange), n = 15. * p < 0.05.