FIGURE 1.

Representative examples of locomotor activity patterns that were used to designate hamsters as entrained (ENT, a1) or circadian-arrhythmic (ARR, a2). Vertical black hash marks indicate daily locomotor movement in the home cage and are double-plotted on a 48-hr time scale with data from consecutive days plotted from top to bottom. Most cage activity occurs at night for ENT hamsters as indicated by the black and white rectangles that indicate night (8 hr) and day (16 hr), respectively. By contrast, locomotor activity in ARR hamsters is distributed equally across 24 hr, indicating the loss of circadian timing. These observations were confirmed by chi-square time series analysis showing a robust daily rhythm with a peak at 24 hr with harmonics at 12 and 36 hr in ENT animals (b1), and a lack of periodicity in the ARR animal (b2)