Deep in the hippocampus of an 83-year-old woman whose memory rivals that of someone half her age, something quietly extraordinary is happening. New neurons are being born. Not the tentative, stuttering output you might expect from a brain eight decades old, but a robust, continuous generation of fresh cells — roughly twice as many as in the brains of her sharp-but-typical peers, and orders of magnitude more than in the brain of someone with Alzheimer’s disease.
How that woman ended up with such a neurologically fertile hippocampus, and what it means for the rest of us, is what a team at the University of Illinois Chicago, Northwestern University and the University of Washington has spent years trying to understand. Their findings, published this week in Nature, don’t just settle a long-running debate about whether adult human brains can grow new neurons at all. They map, for the first time, the precise molecular signature that distinguishes a brain ageing gracefully from one sliding towards dementia.
The debate itself has been bruising. For decades after researchers first observed neurogenesis — the birth of new neurons — in adult rodents, many scientists doubted it happened in humans at all. The hippocampus, the brain’s memory hub, seemed like a plausible candidate; that’s where neurogenesis had been found in mice, where it played a demonstrable role in learning and forgetting. But human brain tissue is notoriously difficult to work with, and early studies using different methods reached contradictory conclusions. Some researchers couldn’t find newborn neurons in adult human hippocampi at all.
The new study cuts through that controversy using technology unavailable even five years ago. The team analysed nearly 356,000 individual cell nuclei extracted from the hippocampi of 38 donated brains, spanning five distinct cognitive groups: young adults in their twenties and thirties; healthy older adults with normal-for-age cognition; so-called superagers; individuals with preclinical signs of cognitive decline; and people diagnosed with Alzheimer’s disease.
The superagers are the star of this story. Defined by the Northwestern SuperAging Programme as adults aged 80 or older whose performance on episodic memory tests equals or exceeds that of people in their fifties, these donors had agreed not only to regular cognitive testing in life but to donating their brains afterwards. In their hippocampi, Orly Lazarov and her colleagues went looking for three developmental stages of new neurons: neural stem cells, neuroblasts — adolescent precursors on their way to becoming neurons — and immature neurons not yet fully integrated into circuits. “Think of the stages of adult neurogenesis like a baby, a toddler and a teenager,” says Lazarov. “All are signs that these hippocampi are growing new neurons.”
What they found in the superager brains was unambiguous. Immature neurons were roughly two-and-a-half times more abundant than in the other aged cohorts. Neuroblasts were significantly elevated compared with Alzheimer’s brains. And crucially, the pattern held even after the team excluded one donor who was a clear outlier. “Superagers had twice the neurogenesis of the other healthy older adults,” Lazarov says. “Something in their brains enables them to maintain a superior memory. I believe hippocampal neurogenesis is the secret ingredient, and the data support that.”
The brains with Alzheimer’s disease told the opposite story. Neural stem cells were present — in fact, somewhat more numerous than in healthy older adults — but the pipeline from stem cell to functional new neuron had broken down almost completely. Neuroblasts and immature neurons were vanishingly rare. The stem cells were there but going nowhere. Even more striking was where the disruption started: in the preclinical group, people who showed no symptoms during life but whose brains carried the earliest biological signs of Alzheimer’s pathology, the neurogenic pipeline was already faltering. The factory had started shutting down before anyone noticed the lights were dimming.
That early signal comes primarily not from changes in gene expression but from something more fundamental — the physical architecture of DNA itself. Using a technique that reads which stretches of chromatin are accessible to gene-activating proteins, the team found thousands of regions that were differentially open or closed depending on cognitive status. These epigenetic changes, it turns out, are a more reliable indicator of neurogenic health than which genes are actually switched on. DNA accessibility shifts early and robustly; gene expression shifts later and more variably. The implication is that the brain’s fate may be written in its chromatin long before any cognitive symptom appears.
For Jalees Rehman, who led the computational side of the study, the research reflects something larger than one paper about memory cells. “Modern medicine has revolutionised health care such that life expectancy is greater now than ever before,” he says. “We need to ensure that this overall increased life expectancy goes along with a high quality of life, including cognitive health.” Ahmed Disouky, the study’s first author, puts it more directly: “The aging brain is not fixed or doomed to decline. Understanding how some people naturally maintain neurogenesis opens the door to strategies that could help more adults preserve memory and cognitive health as they age.”
What those strategies might be remains open. The team’s next step is to examine which lifestyle and environmental factors — diet, exercise, inflammatory load — correlate with the neurogenic signatures they’ve identified. The epigenetic patterns they’ve mapped now offer specific molecular targets: transcription factors, gene regulatory networks, chromatin-remodelling machinery that seems to keep the neurogenic conveyor belt moving in superager brains and grinds it to a halt in Alzheimer’s. Some of these targets, like the signalling molecule BDNF, are already familiar from animal studies. Others are newly identified from this human data.
There is, of course, a chicken-and-egg question lurking here. Do superagers have exceptional memory because their hippocampi keep producing new neurons, or do they produce new neurons because some deeper biological advantage is at play — genetics, lifetime habits, sheer luck? The study cannot fully answer that. What it can say is that the difference is real, measurable and molecularly specific, and that the same signature that defines exceptional ageing is also, in mirror image, the signature of Alzheimer’s disease. Somewhere in that gap between a brain that keeps making new cells and one that stops, there may be a door worth prying open.
Study link: https://www.nature.com/articles/s41586-026-10169-4
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I am 83. I am an Analyst/Programmer who has never stopped doing analysing and programming. My best work has been in the last few months. I strong suspect my brain has benefitted from my A/P work to the point where it is now a Super-brain.