Alzheimer’s can begin changing the brain years, even decades, before memory problems become noticeable. That has made finding the disease as early as possible one of the biggest goals in Alzheimer’s research. But what if some of the changes scientists currently consider “early” are actually arriving relatively late?
For years, the buildup of amyloid plaques has been treated as one of the earliest detectable biological signs of Alzheimer’s disease. PET scans can reveal that buildup before someone develops obvious cognitive symptoms, potentially providing a window into the disease while a person still feels completely healthy.
Now, a 2026 study published in Nature Neuroscience suggests the brain may be changing even earlier. Researchers at the University of Oslo found differences in cortical thickness among cognitively healthy adults at least seven years before they developed the high levels of amyloid detectable on PET scans.
The finding doesn’t mean scientists have discovered a new Alzheimer’s screening test. But it raises a much bigger question about the disease itself: If the brain is already changing before amyloid plaques become detectable, what is actually happening at the very beginning of Alzheimer’s?
The Disease That Starts Long Before You Notice Alzheimer’s Early Signs in the Brain
Alzheimer’s disease is a progressive neurodegenerative disorder characterized by the buildup of amyloid plaques and neurofibrillary, tau-based tangles, with these neuropathological features beginning 15 to 20 years before obvious cognitive symptoms. By the time a person walks into a clinic with memory concerns, the damage has typically been accumulating for well over a decade.
The proposed research consensus in Alzheimer’s disease, as outlined in the Nature Neuroscience study, holds that the presence of amyloid-beta plaques at sufficiently high levels is considered sufficient to establish a biological diagnosis of Alzheimer’s disease. Amyloid-related abnormalities are thought to be the first pathological marker of the disease. Accordingly, changes in amyloid detectable on PET scans are considered the earliest imaging marker, while brain structural alterations detectable with MRI are thought to occur later.
The Oslo study directly challenges that ordering. New imaging data suggest that changes in the brain’s cortical thickness – the thickness of the brain’s outer layer – could precede high levels of amyloid plaques by up to seven years. The study combined longitudinal MRI data with amyloid-beta PET imaging to identify subtle structural changes in the brains of individuals who went on to develop Alzheimer’s.
Anders M. Fjell, Ph.D., co-author and a professor at the University of Oslo, described the finding as examining “changes in brain structure in the years before the first scan revealed plaques.” The participants involved were cognitively well-functioning older adults throughout this period.
What the Scans Actually Show
Amyloid PET imaging represents a significant advance in the assessment of cognitive impairment. The scan visualizes plaques present in the brain – the prime suspects in damaging and killing nerve cells in Alzheimer’s. Before amyloid PET, these plaques could only be detected by examining the brain at autopsy. It’s genuinely powerful technology, but it has a ceiling: it can only detect plaques that have already accumulated above a certain threshold.
MRI works differently. It measures the structure of the brain itself – including cortical thickness, the depth of the brain’s outer layer (the cortex), and the size of specific regions like the hippocampus, the area most associated with memory. Changes in amyloid detectable on PET scans are considered the earliest imaging marker for Alzheimer’s, while brain structural alterations on MRI are thought to occur later – consistent with models of how biomarkers sequence during disease progression. The Oslo finding turns that sequence on its head.
The analysis found that people who eventually showed elevated amyloid plaques had thicker cortical regions and slower rates of cortical thinning compared with individuals who remained amyloid-negative. In people who later developed amyloid positivity, cortical thickness diverges from normal aging trajectories years before plaques reach detectable levels on PET — and the timing of that divergence is what distinguishes it from ordinary age-related change. The difference was detectable years before those same people crossed the threshold to amyloid positivity.
If you’re interested in how other early cognitive shifts can emerge years before a clinical diagnosis, early warning signs of cognitive decline offer additional context on what subtle changes may look like long before a doctor flags anything.
The differences were detectable as early as seven years before participants were deemed amyloid-positive. Some of the cortical thickness differences persisted even after researchers accounted for quantitative amyloid levels, prompting the team to signal that at least some structural changes may occur independently of measurable amyloid accumulation.
The Two Explanations – and Why One Changes Everything
Researchers can’t yet say definitively what’s driving these early structural changes, and the answer matters enormously for how the disease might one day be treated.
The first explanation is that amyloid processes are already underway but simply haven’t reached the level that PET scanning can detect. Amyloid may be present at lower concentrations or affecting the brain through mechanisms that precede large-scale plaque formation. Under this interpretation, the Oslo findings don’t rewrite the biology of Alzheimer’s – they just reveal that amyloid’s effects begin earlier than current technology can see.
The second explanation is more disruptive: something else may be altering brain structure first, before amyloid becomes the dominant driver. As Professor Fjell of the University of Oslo noted, “if the latter is true, it suggests it is important to continue developing drugs that target processes other than amyloid plaque accumulation.” More research is needed to determine which explanation holds.
Alzheimer’s drug development has centered on clearing or preventing amyloid, and treatments that slow progression of early Alzheimer’s disease have been approved by the FDA and other regulatory agencies. Those drugs target amyloid. If some of the earliest brain damage is being driven by something other than amyloid – inflammation, vascular changes, tau processes, or other mechanisms – treating amyloid alone may not be enough to stop the disease at its true beginning.
A Decades-Long Hidden Phase
Alzheimer’s disease begins long before the onset of cognitive symptoms, with pathological changes emerging more than a decade prior to diagnosis. The Oslo research is consistent with a body of work showing just how far back that process starts.
Research tracking genetic forms of the disease has pushed the timeline even further. A study published in Alzheimer’s & Dementia found that amyloid-beta levels significantly increased up to 22 years before symptoms were expected to develop, with an average of 18.9 years. That’s nearly two decades of silent biological activity before a person experiences their first cognitive symptom.
Even subtle thinking and memory changes that precede a clinical diagnosis can begin years before doctors flag anything. A prospective longitudinal study published in Neurology, involving 2,125 participants in Chicago, found that lower performance on tests of episodic memory, executive function, and global cognition was detectable as early as 18 years before a clinical Alzheimer’s dementia diagnosis. Most people in that window would feel entirely normal and pass standard cognitive tests without difficulty.
Pathological changes in the brain begin accumulating decades before cognitive symptoms appear in Alzheimer’s disease. The deposition of amyloid-beta proteins leads to disruption in functional connections between brain networks. Characterizing these changes in the preclinical phase has the potential to help treatment development by targeting the mechanisms that cause cognitive decline before dementia occurs.
Why This Study Is Harder to Dismiss Than Most
Many studies of Alzheimer’s biomarkers are limited by their timeframe. Following patients for three to five years gives a narrow window into a disease that develops across decades. The Oslo research had an unusually long runway.
The Nature Neuroscience study suggests Alzheimer’s disease may be detected by brain imaging more than seven years earlier than previously assumed, with the research led by scientists in the Department of Psychology at the University of Oslo. The paper, titled “Cortical thickness changes precede high levels of amyloid by at least 7 years,” combined data from 4,570 longitudinal MRI scans and 1,684 amyloid PET scans drawn from three cognitively healthy cohorts.
The team used MRI data collected from healthy participants over nearly 20 years – a rare data set in a field where longitudinal studies are expensive and difficult to run. They identified participants whose later PET scans eventually turned positive for amyloid, then looked backward at their MRI records from the years before that happened. That approach allows researchers to see what the brain looked like before the disease crossed the current diagnostic threshold.
The study was published on August 19, 2026, in Nature Neuroscience, volume 29. James Michael Roe, who led the research as a postdoctoral researcher at the Center for Lifespan Changes in Brain and Cognition at the University of Oslo and now serves as International Scientific Lead at Cercare Medical, noted that “structural changes in the brain occur many years before high levels of plaque are seen on PET scans, which is the brain scan currently used to identify the earliest signs of Alzheimer’s disease.”
What This Doesn’t Mean Yet
Clear findings deserve equally clear caveats.
The Nature Neuroscience paper was published as a peer-reviewed observational study – not as a clinical protocol. The study suggests that the current gold standard for Alzheimer’s imaging may not be sensitive enough to detect these earliest brain processes, such as the accumulation of amyloid plaques. But the structural MRI patterns identified in the research are not yet validated as a standalone screening tool.
Brain structure changes with age in everyone. Cortical thinning is a normal part of growing older, and distinguishing the subtle pattern identified in this research from normal aging – or from other neurological conditions – will require much larger studies and independent validation. Amyloid, tau, and FDG PET imaging together enable increasingly accurate diagnosis, staging, and therapeutic monitoring. In the United States, the FDA has approved treatments targeting amyloid, expanded Medicare reimbursement for amyloid PET imaging, and new therapies have ushered in a new era of personalized neuroimaging in Alzheimer’s disease. Routine MRI cannot replace that combination of tools simply because a structural signal appears earlier.
The Oslo researchers acknowledge that further work is needed to determine whether the pre-amyloid changes they found accurately predict future Alzheimer’s disease across diverse populations, and to understand how those changes interact with other known risk factors including tau accumulation, vascular health, genetics, and inflammation.
Read More: Scientists Find an Earlier Warning Sign of Alzheimer’s Than Memory Loss
What This Could Mean for Alzheimer’s Research
The biggest takeaway, then, isn’t that doctors can now detect Alzheimer’s seven years sooner. They can’t. It’s that the disease may be giving off signals earlier than our current tools have been able to see. And those signals could change what scientists consider the true beginning of Alzheimer’s disease.
For now, these findings are more important for researchers than they are for someone sitting in a doctor’s office. The structural patterns identified in the study are not a new screening test, and there is currently no routine way to determine whether a healthy person is experiencing these particular pre-amyloid changes.
What the research may change is where scientists look for the beginning of Alzheimer’s disease. If structural changes really do emerge years before amyloid reaches detectable levels, researchers will need to determine what is driving them. Amyloid could already be involved at levels PET scans cannot see, or other biological processes may begin changing the brain first.
Answering that question could eventually influence both early detection and treatment. Therapies aimed at Alzheimer’s are increasingly being used earlier in the disease process, making it especially important to understand what “early” actually means.
Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.
AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.
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