Four male (ID: 7609, 7648, 7666, 7667) and one female (ID: 7608) Per1-/-;Per2-/-;Per3-/- mice with hemizygous Nr1d1-luciferase transgene, ages 4-5 months old were used for this study. All mice were bred and group housed in a 12L:12D cycle.

Circadian behaviour recordings were conducted in a light-tight ventilated box (Phenome Technologies, Skokie, IL, USA). The mice were singly housed in plastic cages (length×width×height: 29.5×11.5×12.0 cm) with running wheels (diameter: 11 cm) in constant darkness with ad libitum access to regular chow (2018 Teklad Global 18% Protein Rodent Diet; Harlan, Madison, WI, USA) and water throughout behaviour recordings for 272 days. Wheel revolutions were continuously recorded every minute by the ClockLab system (ver. 3.604, Actimetrics, Wilmette, IL, USA). For a small number of data points (0.09%) the PC recorded no value; this occurred at the same time for all mice and appears as NaN.