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You did not sleep through the night. Nobody does.
Several times an hour, while you were unconscious, your brain briefly surfaced. Not enough to open your eyes. Not enough to leave a memory. Just a short burst of faster electrical activity, a few seconds long, and then back down again. Sleep scientists call these arousals, or micro-awakenings, and they are a standard feature of ordinary human sleep. You have had them every night of your life and you have never once noticed one.
Which is what makes a recent finding out of Belgium worth sitting with for a minute.
What Micro-Awakenings Actually Are
Sleep is not a switch. It is closer to a tide.
Across the night you move between lighter and deeper stages, and the passage between them is not smooth. Your brain repeatedly lifts toward the surface, hovers there for a few seconds, and sinks back. A noise outside, a shift in temperature, a slight change in your breathing, or nothing identifiable at all — any of it can trigger one.
These are measured in a sleep laboratory with electrodes on the scalp, because that is the only place they exist as far as you are concerned. There is no felt experience of a micro-awakening. If you were asked in the morning how many you had, you would have no way to guess.
That is the strange part, and it is worth naming plainly before anything else: a real, repeated, measurable event happens inside you every single night, and you have no access to it whatsoever.
They are a different thing from the waking you do remember — the long, annoyed, staring-at-the-ceiling kind that has its own, much less mysterious explanation. Micro-awakenings never reach that far up.
What the Study in Belgium Found
A team at the University of Liège, working through its GIGA neuroscience institute, studied the sleep of more than 500 healthy people. Nobody in the group had memory problems. Nobody had a diagnosis. The results were published in the journal Sleep.
The participants fell into two groups: younger adults, roughly 18 to 31, and middle-aged adults, roughly 50 to 69. Alongside the sleep recordings, the researchers calculated a polygenic risk score for each person — a single number summarising how a large set of common gene variants stacks up with respect to Alzheimer’s disease.
In the older group, people who had more frequent micro-awakenings tended to carry a higher genetic risk score.
In the younger group, that pattern was not there at all.
“These micro-awakenings are therefore not insignificant,” said Puneet Talwar, one of the researchers, adding that certain profiles could “promote the accumulation of proteins involved in Alzheimer’s disease.”
The Part That Is Very Easy to Read Wrong
Here is where most coverage of a study like this quietly goes off the road, so it is worth being slow and exact.
This is an association. It is not a cause, and it is not a test.
The researchers did not find that broken sleep gives anyone Alzheimer’s. They did not find that people with more micro-awakenings will develop it. They found that two things measured in the same group of healthy people moved together — and only in the older half of that group.
The team said so themselves. The findings are statistical associations that need confirmation, and they do not, at this stage, allow the disease to be predicted in any individual person. A polygenic risk score is not a diagnosis either. It cannot tell you whether you will get a disease. It describes a tilt across a population, not a fate for a person.
So if you are reading this at two in the morning having just woken up, this study does not have anything to say about you specifically. Nothing here is a warning sign to check yourself against.
What it might eventually offer is something more useful and far less frightening: a cheap, non-invasive signal that could help researchers spot who to study decades earlier than they currently can.
The Detail Almost Nobody Leads With
Buried in the same work is the thing that actually made me stop.
The Liège team did not only count arousals. They also imaged a structure called the locus coeruleus, using an unusually powerful 7-Tesla scanner, and looked at the quality of REM sleep.
The locus coeruleus is tiny — a smudge of cells in the brainstem, a few millimetres across. It is the brain’s main source of noradrenaline, and it is, functionally, a large part of what wakes you up. Arousal runs through it. When your brain surfaces in the night, this is one of the structures doing the lifting.
And it happens to be the place where, according to a wide body of published work on how Alzheimer’s spreads through the brain, the very earliest traces of the disease’s tau protein tend to appear. Not in the memory centres. There, first — possibly decades before anyone notices anything wrong.
Sit with the shape of that for a second. The structure that runs your waking may be the same structure where the trouble starts.
Nobody has proven that the one explains the other. That is a hypothesis, not a finding, and the honest position right now is that it is unresolved. But it is a much more interesting reason to care about micro-awakenings than “bad sleep is bad for you,” and it explains why researchers keep circling back to this particular corner of the brain.
It also runs in the opposite direction to most of what gets written about sleep and dementia. The more familiar story is about people who already have the disease, and what it does to their nights — including the brain’s own immune cells pulling their sleep apart. This work starts at the other end, with people who are perfectly well.
Getting Older Is Not the Same as Getting Sick
One more number, because it reframes everything above.
A systematic review pooling 169 studies of more than 5,000 healthy adults found that the rate of arousals during sleep climbs steadily with age — by roughly two additional events per hour for every decade of life.
Read that again. In healthy people. With no illness at all.
Your sleep is supposed to get lighter as you get older. A sixty-year-old who wakes more than they did at twenty is not failing at sleeping. They are sixty. The fragmentation is part of the ordinary arc of a human life, not evidence that something has gone wrong in it.
This is exactly why the Liège result is interesting rather than alarming. Everybody in the older group had more arousals than the younger group. The question the researchers were asking was narrower and more careful than “who wakes up too much.”
What to Actually Do About It
Honestly? Almost nothing. And that is not a dodge.
You cannot feel micro-awakenings, so you cannot count them, so there is nothing to monitor. If you take one practical thing from this article, let it be this: do not start trying. Lying in bed auditing your own sleep is a reliable way to sleep worse, and the thing you would be auditing for is invisible to you anyway.
The unglamorous basics still help, and none of them cost anything:
- A consistent wake-up time does more than a consistent bedtime.
- Cooler is better than warmer. Heat pulls you toward the surface.
- Alcohol in the evening reliably fragments the second half of the night, even when it helps you fall asleep faster.
- Light in the morning — even ten minutes of it, even through cloud — steadies the whole system more than anything you do at night.
If your daytime tiredness is severe, or someone has told you that you stop breathing in your sleep, that is worth raising with a doctor. That is a different conversation from this one, and a more urgent one.
If you want a starting point rather than a rule, our free How Much Sleep Do I Need? calculator works out a realistic target from your own schedule instead of repeating the same number at everyone.
The Hours You Never Get to See
There is something in this I have not been able to put down.
Roughly a third of your life happens in a state you have no witness to. You are not absent during those hours — a great deal is going on, some of it consequential, as this research keeps showing. You are simply not there to observe it. Whatever you are at three in the morning, you are it without any input from the part of you that manages how you come across.
Most of us are quietly uneasy about that, and it surfaces in odd ways: people who cannot sleep in an unfamiliar house, people who apologise for snoring, people who feel obscurely embarrassed at being seen asleep. Being unobserved by yourself is a strange kind of exposure.
It is worth noticing that when people across history have talked about being known by God, this is much closer to what they meant than a supervisor keeping score. Not being watched at your best. Being accompanied in the hours you have no access to — the ones where you are not performing, not deciding, not managing anything at all, and are simply a person, breathing, surfacing and sinking, being kept.
You can take that or leave it. It sits there either way.
The Thing Worth Keeping
Tonight your brain will lift toward the surface, hover, and sink again, over and over, and you will remember none of it. That has always been true. The only thing that changed recently is that somebody is finally able to look at it properly.
The waking was never the problem. It is how sleep has always worked. And for the first time, the fact that it can be watched at all is starting to look less like a curiosity and more like a door — the kind researchers may one day walk through years before a single symptom shows up.
That is not a reason to lie awake. If anything, it is the opposite.
One Question for You
Do you think we would sleep better if we stopped treating “sleeping through the night” as the standard — given that, by every measurement we have, nobody has ever actually done it? Tell us what you think in the comments below.
Share This
“Nobody sleeps through the night. Your brain surfaces repeatedly, every night, for seconds at a time — and you have never noticed one of them. They’re called micro-awakenings.”
“Healthy adults get roughly two more sleep arousals per hour for every decade they age. If you wake more at sixty than you did at twenty, you are not failing at sleeping. You are sixty.”
“The tiny brainstem structure that wakes you up in the night is also where the earliest traces of Alzheimer’s tend to show up. Nobody has proven the two are connected. I can’t stop thinking about it.”
Common Questions About Micro-Awakenings
What are micro-awakenings?
Micro-awakenings, also called arousals, are brief bursts of faster brain activity that interrupt sleep for a few seconds without waking the person fully. They are detected with electrodes on the scalp during a sleep study and are not consciously felt or remembered. They occur several times an hour in normal, healthy sleep and are considered a standard feature of it rather than a disorder.
Are micro-awakenings normal, or a sign something is wrong?
They are normal. Every sleeper has them, every night. A systematic review pooling 169 studies of more than 5,000 healthy adults found the rate of arousals rises with age by roughly two additional events per hour for each decade of life, in people with no illness at all. Lighter, more fragmented sleep is part of ordinary ageing rather than evidence of disease.
What did the University of Liège study on micro-awakenings find?
Researchers at the University of Liège in Belgium studied the sleep of more than 500 healthy people in two age bands, roughly 18 to 31 and roughly 50 to 69, and published the results in the journal Sleep in 2026. Among the older participants, more frequent nocturnal micro-awakenings were associated with a higher polygenic risk score for Alzheimer’s disease. No such association appeared in the younger participants. All participants were healthy and none had symptoms.
Do micro-awakenings mean I will get Alzheimer’s disease?
No. The Liège finding is a statistical association observed across a group, not a cause and not a diagnostic test. The researchers stated explicitly that the results require confirmation and do not, at this stage, allow the disease to be predicted in any individual. A polygenic risk score summarises the combined effect of many common gene variants across a population and cannot determine whether a particular person will develop Alzheimer’s.
What is the locus coeruleus, and why does it come up in sleep and Alzheimer’s research?
The locus coeruleus is a small cluster of cells in the brainstem, a few millimetres across, that supplies most of the brain’s noradrenaline and plays a central role in arousal and waking. It draws attention in Alzheimer’s research because a substantial body of published work indicates it is among the earliest sites where the disease’s tau protein appears, potentially decades before symptoms. The Liège team imaged it using a 7-Tesla scanner as part of their sleep study. Whether its role in waking and its role in early disease are connected has not been established.
