Exogenous Timing of Rat Spontaneous Activity Periods. †

Summary

1. A white rat displayed in constant low illumination a rhythm of spontaneous running of precise lunar-day frequency over 60-day study. This obviously resulted in accurate monthly recurrence of daily running patterns. 2. Activity was high during hours the moon was below the horizon, and low when above. Spontaneous running at first lunar hour was 6 times that at 11th hour. Correlation between average lunar-day cycles for 2 consecutive months was +0.70 ± 0.11. and mean cycle for each month was quite similar to earlier published lunar-day cycle in the rat. 3. Superimposed upon the dominant lunar-day periodism were minor, transient, solar-day patterns of locomotor activity, terminating spontaneously or through apparent submergence in the larger amplitude, lunar-day cycles. 4. Since these 2 basic periodisms in rat activity, solar-day and lunar-day, are the same frequencies as the widely, and probably universally, distributed exogenous metabolic periodisms, they are considered simple behavioral expressions of a fundamental exogenous “clock-system” from which regular physiological rhythms of other than natural frequencies, often present, may be derived by the organism.