Alzheimer's disease begins quietly: deep in the brain, two proteins, tau and amyloid-beta, start to accumulate. They behave like weed seeds: one clump that appears causes neighboring cells to produce similar clumps. Gradually, the proteins spread along nerve fibers, like water through the capillaries of a paper towel, and invade new areas.
The brain shrinks as a result. In a healthy person, it's like a sponge filled with water; in Alzheimer's, it's like a dried-out sponge: it loses volume, the sulci become deeper, and the ventricles enlarge. Scientists have long seen this on scans but couldn't link the picture to microscopic processes.
Now, in Oxford, they've built a computer model that bridges both levels. You load a patient's MRI into it, and the program automatically reconstructs the brain's shape and the directions of nerve fibers. Then a simulation runs: proteins spread along the fibers, and the tissue responds by losing volume. After a few virtual years, the model shows exactly how this person's brain will change.
It's like a weather forecast for the brain. Instead of cyclones and precipitation, there's a map of protein spread and zones of future shrinkage. A doctor could see in advance which areas will be hit hardest and choose therapy before obvious symptoms appear. And the model itself, along with the software for processing scans, has been made open access: any researcher can download and adapt it to their own needs.
The speed at which tau protein spreads through the brain is roughly 1–2 millimeters per year: that's a hundred times slower than a fingernail grows.