Journal of biological rhythmsMay 16, 2022

Detailed Timing Analysis Shows Ongoing Daily Behavior Rhythms in Mice Without Normal Body Clocks

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗OA ↗

Updated Mar 29, 2026

Abstract

Four rhythmic components with periods of ∼17 h, ∼8 h, ∼4 h, and ∼20 min were identified in mice lacking the canonical circadian clock.

Circadian rhythms are internal processes repeating approximately every 24 hours, primarily synchronized to environmental light-dark cycles.
, which are shorter than circadian rhythms, are less understood in terms of their biological mechanisms and significance.
In the absence of the canonical circadian clock, distinct rhythmic components were observed, including periods of approximately 17 hours, 8 hours, 4 hours, and 20 minutes.
The presence of the ∼17-h rhythm correlated with a low amplitude of the ∼8-h rhythm, occurring in a periodic manner every 2-3 weeks.
The ∼4-h and ∼20-min rhythms were found to be harmonics of the ∼8-h rhythm, indicating a structured relationship among these oscillators.
Strong was observed from slower rhythms (∼17, ∼8, and ∼4 h) to faster rhythms (∼20 min), while coupling in the reverse direction was weak.

Simplified

Circadian rhythms are internal processes repeating approximately every 24 hours in living organisms. The dominant circadian pacemaker is synchronized to the environmental light-dark cycle. Other circadian pacemakers, which can have noncanonical circadian mechanisms, are revealed by arousing stimuli, such as scheduled feeding, palatable meals and running wheel access, or methamphetamine administration. Organisms also have , which have periods shorter than circadian rhythms. However, the biological mechanism, origin, and functional significance of ultradian rhythms are not well-elucidated. The dominant circadian rhythm often masks ultradian rhythms; therefore, we disabled the canonical circadian clock of mice by knocking outgenes, whereandare essential components of the mammalian light-sensitive circadian mechanism. Furthermore, we recorded wheel-running activity every minute under constant darkness for 272 days. We then investigated rhythmic components in the absence of external influences, applying unique multiscale time-resolved methods to analyze the oscillatory dynamics with time-varying frequencies. We found four rhythmic components with periods of ∼17 h, ∼8 h, ∼4 h, and ∼20 min. When the ∼17-h rhythm was prominent, the ∼8-h rhythm was of low amplitude. This phenomenon occurred periodically approximately every 2-3 weeks. We found that the ∼4-h and ∼20-min rhythms were harmonics of the ∼8-h rhythm. Coupling analysis of the ridge-extracted instantaneous frequencies revealed strong and stable from the slower oscillations (∼17, ∼8, and ∼4 h) to the faster oscillations (∼20 min), and weak and less stable phase coupling in the reverse direction and between the slower oscillations. Together, this study elucidated the relationship between the oscillators in the absence of the canonical circadian clock, which is critical for understanding their functional significance. These studies are essential as disruption of circadian rhythms contributes to diseases, such as cancer and obesity, as well as mood disorders. Per1/2/3Per1Per2

Key numbers

17 h, 8 h, 4 h, 20 min

Oscillation Periods

Four distinct rhythmic components were observed.

192

Coupling Strength

Mean coupling strength between oscillations when above the surrogate threshold.

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Detailed Timing Analysis Shows Ongoing Daily Behavior Rhythms in Mice Without Normal Body Clocks

Abstract

Key numbers

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