It’s as inevitable as grey hair and wrinkles—when we get old, our memories decline, even if Alzheimer’s or dementia doesn’t accelerate that process. But there are a select few whose memories seem to remain as hale as those decades younger. Scientists call them superagers. And now, there is some clarity as to how these superagers hold on to their robust memory.

In superagers, the brain networks used for memory, learning, and resilience are nearly untouched by age. While other areas of their brains atrophied, the memory networks of superagers aged 60 to 80 were as healthy as those of the average 18-to-32-year-old’s brain, researchers at Massachusetts General Hospital reported recently in the Journal of Neuroscience. “We were surprised by that,” said Alex Touroutoglou, a researcher in neurology at Massachusetts General Hospital and a co-author of the study.

While some earlier evidence of “superaging” had been found in the brains of patients older than 80, the new results show how the trait can appear in brains up to two decades younger.

By watching how superagers avoid some of the consequences of normal aging, the researchers hope to understand and alleviate both the slow decline of healthy aging and the diseases that accelerate it.

To measure brain health, Touroutoglou and her collaborators examined the cortex, the layer on the surface of our brains rich in grey matter. Only a few millimeters thick, the cortex coats the brain’s distinctive folds and is involved in many of the advanced thought patterns that are hallmarks of our humanity—like language, memory, and consciousness. But as we age, that cortex grows thinner, reducing the brain’s cognitive resources. By measuring the thickness of this cortex, then, scientists can see how much aging has degraded that part of the brain.