Scientists have discovered a potential brain-based signal that may help detect early cognitive decline in Alzheimer’s disease.
A new study by researchers from Université Savoie Mont Blanc, Radboud University, and the University of Oxford reports that changes in the brain’s natural balance between two major systems—the default mode network (DMN) and the dorsal attention network (DAN)—may serve as a marker of Alzheimer’s risk.
Normally, these two networks operate in an on/off relationship. When a person is daydreaming or remembering the past, the default mode network is active. But when they are focusing on a task, the dorsal attention network takes over.
The two systems help the brain switch smoothly between rest and action. In healthy brains, these two networks typically do not activate at the same time.
However, the researchers found that in people with Alzheimer’s disease, this clear separation fades. Using brain scans from 182 participants in the Alzheimer’s Disease Neuroimaging Initiative (ADNI), the researchers measured how strongly the two networks were “anticorrelated”—meaning when one turns on, the other turns off.
In people with higher levels of amyloid plaques in the brain and signs of cognitive decline, the anticorrelation between these networks was weaker. In simple terms, their brain systems were more muddled, which could make it harder to concentrate or remember things.
This change in brain activity was found to be partly independent of tau protein buildup and a person’s education level (used as a marker of cognitive reserve). This means that the breakdown in the brain’s network separation may be an early warning sign of cognitive problems, even before major structural damage or symptoms occur.
The researchers used resting-state fMRI, a type of brain scan that looks at natural brain activity when the person is not performing any task. They compared this with other scans that show amyloid and tau buildup, as well as results from memory and cognitive tests.
They discovered that weaker DMN-DAN separation was linked to lower scores on a range of cognitive assessments, including the Mini-Mental State Examination and other memory and thinking tests.
Interestingly, even when adjusting for age, sex, tau levels, and education, this network imbalance still explained about 5% of the differences in cognitive performance. That’s a significant number for a single brain measure.
This discovery is important because Alzheimer’s disease has long lacked a single, reliable biomarker that can show exactly when and where brain damage starts. Most current tools focus on protein buildup, like amyloid and tau. But this new measure captures how well brain systems are working together, offering a more functional view of brain health.
The research team suggests that this brain network signal may help explain why some people with high tau levels stay sharp, while others experience rapid decline. It may also point toward new treatment targets—possibly aiming to restore balance between brain networks before memory loss begins.
In the future, scientists hope to explore whether these brain network changes come before or after protein buildup, and whether lifestyle changes or treatments can protect or restore normal brain activity patterns. They also want to build more complete models that combine brain scans, protein levels, and daily habits to better predict who is at risk.
In short, this study reveals that losing the balance between brain networks may be one of the earliest signs of Alzheimer’s disease—and it could help doctors detect and treat the disease much earlier than is currently possible.
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The study is published in NeuroImage.
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