- Lizards and mice share a ~0.02 Hz sleep rhythm that may have evolved 320 million years ago.
- This infraslow oscillation drives the brain's glymphatic waste-clearance system in mice.
- A common sleep medication (zolpidem) suppresses glymphatic clearance by roughly 30%.
Paul-Antoine Libourel’s team of neuroscientists at CNRS in Lyon recorded brain activity from panther chameleons, when they noticed something odd. As the lizards slept, their skin flickered between light and dark in a slow, steady pulse, one cycle roughly every 50 seconds.
The rhythm wasn’t random. It synchronized precisely with fluctuations in the chameleons’ brain waves, eye movements, heart rate, and breathing.
The same rhythm appeared in bearded dragons, Argentine tegus, and tokay geckos. Paul-Antoine Libourel’s team studied seven lizard species in total. Their findings, published December 29, 2025 in Nature Neuroscience, showed this infraslow oscillation organizing the sleeping brain and body into a single coordinated system.
This would be a curiosity about reptile sleep, except for what another team discovered earlier this year.
Key figure
30%
drop in glymphatic clearance caused by zolpidem (a common sleep medication) in mice
The Brain’s Cleaning Cycle
In January 2025, Maiken Nedergaard’s group at the University of Copenhagen and Rochester published findings in Cell. They showed that the same 0.02 Hz rhythm drives the brain’s waste-clearance system in mice. During deep sleep, norepinephrine pulses from the brainstem trigger rhythmic contractions in blood vessels, roughly once every 50 seconds.
It’s like turning on the dishwasher before you go to bed and waking up with a clean brain.
Maiken Nedergaard, University of Copenhagen and University of Rochester
These contractions pump cerebrospinal fluid through the brain, flushing out metabolic debris including the proteins linked to Alzheimer’s disease.
What is the glymphatic system?
The glymphatic system is the brain’s waste-disposal network. While you sleep, cerebrospinal fluid flows through channels surrounding blood vessels, flushing out toxic proteins and metabolic byproducts that accumulate during waking hours. It works mainly during deep sleep, which is why poor sleep has been linked to a build-up of the proteins associated with Alzheimer’s disease.
The critical finding was precision. Random fluctuations didn’t work as well. The brain needed that specific slow rhythm to maximize waste clearance.
When the researchers tested zolpidem, one of the most commonly prescribed sleep medications, they found it suppressed glymphatic clearance by roughly 30%. The drug induced unconsciousness without preserving the oscillations that drive the cleaning cycle.
An Ancient Mechanism
Reptiles and mammals last shared a common ancestor roughly 320 million years ago, during the Carboniferous period. That’s 90 million years before the first dinosaurs.
If both lineages retained this infraslow sleep rhythm, the mechanism is genuinely ancient.
If both lineages retained this infraslow sleep rhythm, the mechanism is genuinely ancient. It predates the evolution of the neocortex. It predates the split between warm-blooded and cold-blooded metabolisms.
In bearded dragons, Libourel’s team observed pulsatile fluctuations in cerebral blood volume during sleep, synchronized to the infraslow oscillation.
This mirrors exactly what Nedergaard’s team documented in mice: vascular pulsations that drive fluid through the brain. The lizard researchers noted that their findings “may advance the glymphatic hypothesis,” suggesting reptiles might use this rhythm for brain clearance too.
Two research programs, developed independently on different continents. One ancient rhythm.
What Remains Unknown
The connection between these papers remains an inference. The lizard study documented vascular coupling but did not test glymphatic function directly. Whether reptiles actually clear brain waste using this rhythm remains to be demonstrated.
The REM sleep question adds complexity. Some researchers argue that eye movements in sleeping reptiles represent a primitive form of REM sleep. Antoine Bergel, the study’s lead author, proposed that the infraslow rhythm might be more fundamental than the REM/non-REM distinction itself.
These cycles are a central thing, maybe a core building block of sleep.
Antoine Bergel, Centre National de la Recherche Scientifique
The human implications also require caution. A 2018 PNAS study found evidence that a single night of sleep deprivation increased amyloid-beta accumulation in the human brain. But establishing direct causation between sleep disruption and neurodegeneration is methodologically difficult.
The Signal
The chameleons can’t help but show us what’s happening in their brains, wearing their sleep rhythms on their skin. For humans, the signal is quieter.
But two papers now point at the same ancient mechanism. The rhythm that cleans your brain tonight may have cleaned your ancestors’ brains before there were mammals.
The next step is clear: test whether reptiles actually use this rhythm for glymphatic clearance.
And test whether preserving our natural sleep architecture protects against neurodegeneration better than pharmacological intervention.
Sources
- Primary Research:
- Bergel, A., Schmidt, J.M., Barrillot, B. et al. (2025). Sleep-dependent infraslow rhythms are evolutionarily conserved across reptiles and mammals. Nature Neuroscience. https://www.nature.com/articles/s41593-025-02159-y
- Hauglund, N.L., Andersen, M., Tokarska, K. et al. (2025). Norepinephrine-mediated slow vasomotion drives glymphatic clearance during sleep. Cell, 188(3), 606-622. https://www.cell.com/cell/fulltext/S0092-8674(24)01343-6
- Additional Context:
- Discovery of an essential sleep rhythm that appeared 300 million years ago (CNRS)
- How deep sleep clears a mouse’s mind, literally (EurekAlert/Cell Press)
- Researchers discover the pump for the brain’s washing machine (University of Copenhagen)
- Snoozing dragons stir up ancient evidence of sleep’s dual nature (The Transmitter)
- Shokri-Kojori, E. et al. (2018). Beta-Amyloid accumulation in the human brain after one night of sleep deprivation. PNAS, 115(17), 4483-4488. https://www.pnas.org/doi/10.1073/pnas.1721694115
Fact Check: Claim-by-Claim Verification Verified
Limits and uncertainties
The core scientific claims are well-supported by peer-reviewed research in Nature Neuroscience and Cell. The evolutionary timeframe is established paleontological consensus. The key uncertainty, which the article explicitly acknowledges, is that the synthesis connecting these two papers is inferential. The lizard study documented vascular coupling but did not test glymphatic function directly. Whether reptiles actually use this rhythm for brain waste clearance remains to be demonstrated experimentally.
Bottom line
The article is factually accurate. Both primary research papers are peer-reviewed and published in top-tier journals. The synthesis connecting them is clearly framed as reasonable inference rather than proven fact, maintaining appropriate epistemic calibration throughout.
Fact-checked by Perplexity Sonar Pro on 2025-12-31
