Figure 2.

Early runner mice exhibit early daily awakening when tested on a piezoelectric system in the absence of a wheel. Data for 4 consecutive LD 12:12 cycles recorded from 4 (B6 × CAST) × CAST backcross mice are shown. Timing of light/dark is indicated both by gray shading and the white/black bar at the top of each panel. Dashed lines show the computer-defined onset for the major wake period within each LD cycle. Sleep-wake patterns and wake onset assessed by the piezoelectric system closely matched wheel-running patterns and onsets, as shown by these 4 examples: (A) A mouse with previous wheel running onset approximately 1 h before dark; (B) and (C) Mice with previous wheel running onsets 3 h prior to dark; (D) Mouse with wheel running onset 5 h before dark. In general, all mice examined had similar activity onsets whether assessed by wheel running, or, several weeks later, by piezoelectric defined sleep and wake.