Circadian Disruption Alters Rhythmic Gene Expression in the Hippocampus Without Changing Overall Levels
New research in rats shows that environmental circadian disruption rewrites the daily rhythm of clock and memory genes in the hippocampus without altering how much of those genes are expressed. The finding suggests that cognitive deficits linked to shift work and jet lag arise not from a simple decrease in gene activity but from a collapse of coordinated timing among the brain’s molecular clocks.
The modern world is a circadian warzone. Shift workers rotate between day and night schedules. Travelers cross time zones in hours. Screens flood the retina with blue light deep into the evening. All of these behaviors disrupt the brain’s internal 24-hour timing system, and a growing body of evidence links that disruption to poor memory, impaired learning, and an elevated risk of neurodegenerative disease. But exactly how a broken circadian clock translates into a broken memory has been surprisingly difficult to pin down at the molecular level.
A team of researchers led by Scott Deibel at the University of Lethbridge has taken a detailed look inside the hippocampus, a seahorse-shaped brain region critical for memory formation, to find out what actually happens to gene expression when the circadian system is thrown into chaos.
The experiment: forcing desynchrony
The researchers used a well-established “forced desynchrony” model in rats. Instead of a standard light-dark cycle, the animals were kept on a 22-hour day (11 hours of light, 11 hours of dark) for three weeks. This schedule is too short for the brain’s master clock to entrain to, so the internal circadian system falls out of alignment with the external environment and, critically, different clocks within the brain begin to drift out of sync with one another.
After three weeks on this disrupted schedule, the team collected hippocampal tissue from both the experimental animals and a control group on a normal 24-hour cycle. They sampled across multiple time points throughout the day, then used quantitative real-time PCR to measure the expression of eight key genes: four core clock genes (Per2, Cry2, Bmal1, Rev-ErbA) and four genes associated with memory and synaptic plasticity (NGFI-A, Arc, BDNF, CREB).
What they found: rhythm rewritten, volume unchanged
The results were striking, and counterintuitive. When the researchers measured the average expression level of each gene across the entire day, there was essentially no difference between the disrupted and control groups. The total amount of each gene product produced over 24 hours was the same.
But the rhythm was profoundly different.
In control animals, each gene showed a clear daily oscillation: expression would rise to a peak at a predictable time and fall to a trough hours later. In the disrupted animals, the rhythmic pattern was reconfigured. Some genes shifted their peak timing by several hours. Others lost amplitude, meaning the daily swing between high and low expression was blunted. A few showed changes in period length, the biological equivalent of a clock running slightly fast or slow.
In short, the cells were still making the same amount of each gene product, but they were making it at the wrong times relative to each other and to the outside world.
“The rhythmic properties changed, but the mean expression didn’t,” the authors write. “This indicates that cognitive deficits associated with circadian disruption may be driven by a failure to maintain circadian synchrony rather than by changes in overall expression magnitude.”
Why it matters: timing is the message
The finding reframes how we think about circadian disruption. For years, the implicit assumption has been that disrupting the clock must suppress or degrade something, less BDNF, less Arc, less synaptic support. The new data suggests that the problem is not one of quantity but of coordination.
Think of the hippocampus as an orchestra. Each gene is a musician playing a part in a complex symphony that unfolds over 24 hours. Circadian disruption does not tell the musicians to play more quietly or to stop playing. It hands them a different sheet of music, one where the entries are mistimed and the cues are scrambled. The volume is the same. The piece is unrecognizable.
This distinction matters for treatment. If the core deficit were simply reduced expression of memory-related genes, the therapeutic approach would be straightforward: boost the levels. But if the problem is a breakdown of temporal coordination, the solution is more subtle and more interesting. It may involve resetting the timing of gene expression, strengthening the coupling between cellular clocks, or developing interventions that protect rhythmic synchrony against environmental disruption.
Limits of the study
Several caveats are important. This work is a preprint posted on bioRxiv and has not yet undergone peer review. The sample size is modest, and the study used only male rats, which limits generalizability. The forced desynchrony model, while well validated, is an extreme protocol that may not perfectly mirror the milder circadian disruption experienced by most human shift workers or frequent travelers. Finally, the study measured gene expression at the RNA level, which does not always predict protein levels or functional changes in the neurons themselves.
The bottom line
Circadian disruption does not silence the hippocampus’s memory-related genes. It unmoors their daily rhythm, scattering the coordinated peaks and troughs that the brain depends on for healthy function. The message of this study is simple yet profound: in the molecular biology of memory, when you say something may be just as important as how much you say.
Source: Deibel SH, Lehr AB, Michalopoulou S, Husain I, Fornasiero EF, Bye C, Hong N, Kovalchuk O, McDonald R. “Circadian rhythm disruption alters rhythmic properties of clock and memory gene expression in the hippocampi of rats.” bioRxiv (preprint), posted July 21, 2026. DOI: 10.64898/2026.07.15.738771
Data availability: figshare, https://figshare.com/s/3a03395842661be6db25
Funding: Natural Sciences and Engineering Research Council (NSERC) 06347, PDF-517352-2018; University of Gottingen; NIH Common Fund 1R21AG085062-01
Competing interests: Andrew B Lehr is co-founder and shareholder of Circulant Labs (Circulant GmbH). Other authors declare no competing interests.