Fig. 1.

Actograms and periodograms for wheel-running activity of individual WT (a) and Vipr2^−/− (b and c) mice expressing the Per1::GFP transgene. Both WT and Vipr2^−/− mice synchronize locomotor activity to a 12 h : 12 h LD cycle. All WT mice free-run in constant darkness with a clear, coherent circadian rhythm (a) but Vipr2^−/− mice express a continuum of behavioral phenotypes from clearly rhythmic (b) to arrhythmic (c). Actograms are double plotted showing two consecutive days data on each line, light and shaded areas represent lights on and off, respectively. Straight diagonal line on periodogram indicates significance at p < 0.001.