AIBRIEF
A small change in cortical thickness, the brain's outer layer, shows up on MRI up to seven years before PET scans flag amyloid beta, the protein buildup that defines Alzheimer's today.
MRI scans can pick up a small change in the brain's outer layer up to seven years before the protein buildups used to diagnose Alzheimer's appear on PET scans. The change is the opposite of what researchers expected: a slightly thicker, not thinner, cortex.
In a study of more than a thousand participants in long-term brain-aging cohorts, published in Nature Neuroscience on Aug. 19, 2026, people who later developed high amyloid-beta levels started with a cortex a few hundredths of a millimeter thicker than their peers. The average cortex is about 2.5 millimeters thick, so the difference is a research signal, not a screening tool.
Amyloid-beta is the sticky protein fragment whose buildup defines Alzheimer's under current PET-scan criteria. PET imaging, not the MRI used here, is what clinicians rely on today, and most people without symptoms do not get a PET scan.
The trajectory reverses: future amyloid-positive participants showed a thicker cortex early, then thinned less with age than controls. No link was observed between this early thickness difference and memory problems at the pre-symptomatic stage, and the team cautions the effect is too small for clinical use.
Victor Montal, a co-author, told Science News the finding reframes how researchers think about early Alzheimer's. The authors say the payoff is for how scientists model the disease and recruit into trials, not for today's patients.