Most of us picture Alzheimer's risk in familiar terms. Age, family history, what we eat, how we sleep, how much we move. The idea that the shape of your own brain could matter is new.
That is the question a team of researchers is beginning to ask. In a study published in October 2026 in Alzheimer's & Dementia, scientists at Columbia University, Mount Sinai and Northwell Health took a hard look at the question.
They examined whether the way the brain fits inside the skull could change the odds of developing Alzheimer's disease.
The research is at an early stage. But the finding is unusual enough that it has drawn attention outside the lab.
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Why a thin fold of tissue above the brain stem matters
Inside the skull, a tough membrane called the tentorium cerebelli separates the cerebellum from the rest of the brain. It has a hard, horseshoe-shaped opening known as the tentorial notch.
Just above that opening sits the entorhinal cortex. It is a small memory hub, and one of the first regions damaged in Alzheimer's.
The Columbia team built a measurement they call the Neuroanatomical Contact Coefficient. It captures how closely the entorhinal cortex sits to the rigid edge of the tentorial notch.
They then followed 47 older adults with mild cognitive impairment, a stage of memory trouble that sometimes progresses to Alzheimer's. Over three years, 24 of them developed the disease. 23 did not.
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In people whose entorhinal cortex sat tight against the tentorial notch, a buildup of tau was linked to developing dementia over the next three years. Tau is a toxic protein that forms tangles inside brain cells and is a signature of Alzheimer's.
In people with more space between the two structures, the same tau signal did not predict who would decline.
What the researchers think is going on
The team proposes what they call a biomechanical cascade. Chronic, low-level pressure from the hard edge of the tentorial notch against the soft tissue of the entorhinal cortex may act a little like repetitive mild head trauma.
Over decades, that pressure could nudge the region toward tau damage sooner than it would otherwise.
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This is a hypothesis, not a proven mechanism. The study was small and did not test treatments. The architecture of the brain alone did not predict who would get Alzheimer's. It only mattered when combined with tau buildup.
The work builds on a larger study of brain geometry. In October 2025, Michael Yassa and colleagues reported in Nature Communications that the brain quietly reshapes itself with age. Yassa directs the Center for the Neurobiology of Learning and Memory at UC Irvine.
They analyzed more than 2,600 scans from adults aged 30 to 97. The lower and front parts of the brain pushed outward, while the upper and back regions pulled inward. The UCI group suggested this shift may press the entorhinal cortex closer to the hard base of the skull.
How this fits next to what we already know
An estimated 7.4 million Americans aged 65 and older are living with Alzheimer's dementia, according to the Alzheimer's Association's 2026 Facts and Figures report.
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The best-established risk factors remain age, genetics and a set of modifiable habits. Sleep, diet, physical activity, mental stimulation, protecting the head from injury, and not smoking.
Head shape is not on that list. The new work does not change what people should do day to day. It is not a test anyone can take at a clinic, and no one is recommending scans to measure the tentorial notch.
The research does open a different question. Why does the entorhinal cortex, out of the whole brain, so often become the first place tau tangles appear?
The Columbia team drew its data from the ADNI database, a long-running US study of memory and aging. The authors describe the proximity score as a potential new biomarker of Alzheimer's risk that will need to be tested in larger groups before any clinical use.
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This article is made and published by Aksel Kryhlmand, who may have used AI in the preparation.