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Representative double-plotted home-cage locomotor activity records of two hamsters housed in each photoperiod (15 L,left column), (13 L, center column), and (9 L, right column). Clock time is indicated on the horizontal axis at the top of each actogram, along with light (white) and dark (black) phases of the photocycle. The shaded area overlapping the activity record denotes the daily dark phase.
