Fig. 1:

Schematic single and double plotted actograms and masking. (A) Wheel-running activity is plotted as an actogram with each horizontal line corresponding to one day. Black vertical bars plotted side-by-side represent the activity, or number of wheel revolutions. The height of each vertical bar indicates the accumulated number of wheel revolutions for a given interval (e.g. 5 min). The rho- and alpha-phase marked at the bottom of the actogram refer to rest and activity, respectively. The white and black bar at the top of the scheme depicts light (12 h) and darkness (12 h), respectively. (B) To better visualize behavioral rhythms, actograms are often double plotted by aligning two consecutive days horizontally (e.g. day 1 left and day 2 right). (C) Schematic actogram of a nocturnal animal kept in very short photoperiods (LD 6:6). Since the animal is only showing activity during the dark phases it seems to entrain to the prevailing LD cycle. (D) Parallel monitoring of body temperature reveals that this apparent entrainment is only masking. Although the readout parameter "activity" seemingly adapts to the new schedule, body temperature continues to cycle with its free-running period length implicating that the circadian clock of the animal is not entrained. LD, light-dark cycle.