NOTE: This article is based on a preprint (DOI: 10.64898/2026.01.06.697926) that has not yet undergone peer review. The findings should be considered preliminary until validated through the formal peer review process.
Lead
You have likely been told that a good night’s sleep helps you remember what you learned during the day. But the mechanism behind that familiar advice has remained surprisingly mysterious. Now a team of neuroscientists has traced the link between your heart and your memory to a single, tiny cluster of neurons deep in the brainstem. In a new preprint posted to bioRxiv, researchers led by Sofie Jacobsen at the University of Copenhagen and the University of California, Irvine show that infraslow rhythms of norepinephrine released by the locus coeruleus during non-rapid eye movement (NREM) sleep are the critical bridge connecting heart rate fluctuations to memory consolidation. The finding opens the door to using simple, wearable heart rate monitors as a window into the brain’s memory machinery.
What they found
The locus coeruleus, or LC, is a small nucleus in the brainstem that acts as the brain’s arousal hub. During wakefulness, it releases norepinephrine to keep you alert. But the LC does not switch off during sleep. Instead, it fires in slow, rhythmic bouts every 30 to 60 seconds, producing an infraslow oscillation of norepinephrine that pulses through the cortex at roughly 0.02 Hz. Previous work had shown that these infraslow norepinephrine waves gate the appearance of sleep spindles, brief bursts of brain activity during NREM sleep that are essential for transferring memories from short-term storage in the hippocampus to long-term storage in the cortex.
In this study, Jacobsen and colleagues asked whether the same norepinephrine rhythm also drives the very-low-frequency fluctuations of heart rate visible on an electrocardiogram. They used optogenetics in mice to answer the question with causal precision. When they inhibited LC activity during NREM sleep, the normally present slowing of heart rate was blunted. When they activated LC neurons directly, the heart rate accelerated almost immediately. The connection was direct and unambiguous: the locus coeruleus controls heart rate dynamics during sleep.
The team then showed that this relationship carries functional significance for memory. In mice, the amplitude of heart rate decelerations during NREM sleep correlated with spindle activity and with how well the animals performed on memory tasks the next day. The same pattern held in human participants. People with stronger very-low-frequency heart rate variability during NREM sleep showed increased spindle expression and better overnight memory retention.
The study brings together three major players in sleep neuroscience: the locus coeruleus, the noradrenergic infraslow rhythm, and heart rate variability. Each has been studied in isolation, but this is the first time the causal chain from LC firing to cardiac signal to memory outcome has been demonstrated in a single, cross-species framework.
Why it matters
The potential clinical applications are significant. The locus coeruleus is one of the first brain regions to degenerate in Alzheimer’s disease and Parkinson’s disease, often years before other symptoms appear. Currently, detecting early LC dysfunction requires expensive PET imaging or invasive cerebrospinal fluid analysis. If the infraslow heart rate fluctuations that the LC drives during sleep can be captured with a simple wearable device, it could provide an early, noninvasive indicator of neuromodulatory decline.
“There is a critical need for early markers of neurodegenerative disease that are accessible, affordable, and scalable,” said senior author Celia Kjaerby, a researcher at the Center for Translational Neuromedicine at the University of Copenhagen. “Sleep is a window into brain health that we have only begun to exploit.”
The study also adds an intriguing new dimension to the relationship between heart and brain. We tend to think of the heart as a pump and the brain as a computer, but the two are locked in a continuous, rhythmic dialogue that persists even when we are unconscious. The infraslow norepinephrine wave is the conductor of that dialogue, and its rhythm appears to be essential for the brain to file away the day’s experiences.
The author list includes Maiken Nedergaard, the neuroscientist who pioneered the discovery of the glymphatic system, the brain’s waste clearance pathway that is also active during sleep, and Sara Mednick, a leading sleep and memory researcher. Their presence underscores the interdisciplinary nature of the work.
Limits
As a preprint, this study has not yet been peer reviewed, and the findings should be regarded as preliminary. The human data is correlational: while the mouse experiments establish causation, the human arm of the study demonstrates association between heart rate variability and memory performance, not direct causality. The sample sizes in both the animal and human experiments, while adequate for the reported effects, are modest and will need replication in larger cohorts. Additionally, translating a heart rate-based biomarker of LC function into a clinically useful tool will require validation in diverse populations and against established biomarkers of neurodegeneration over longitudinal timescales.
Bottom line
Your heart rate during sleep is not random noise. It is a signature of the brain’s norepinephrine rhythm, driven by the locus coeruleus, and it is directly tied to how well your brain consolidates memories. This study provides the clearest mechanistic link to date between cardiac activity during NREM sleep and the neural processes that support memory. It also suggests that the pulse you feel on your wrist at night might one day tell your doctor something about the health of your deepest brain structures, years before any symptoms arise.
Source
Jacobsen SS, Morehouse AB, Chen PC, Qian Y, Gomolka RS, Andersen M, Nedergaard M, Mednick SC, Kjaerby C. Noradrenergic infraslow rhythm during sleep is the critical link between heart-rate dynamics and memory consolidation. bioRxiv [Preprint]. 2026 Jun 25:2026.01.06.697926. DOI: 10.64898/2026.01.06.697926. PMID: 42395575. PMCID: PMC13321006.