Alzheimer’s disease is driven by a buildup of a toxic protein called Tau that kills neurons. As toxic Tau spreads to new regions of the brain, symptoms worsen and ultimately become fatal.

Now, researchers have discovered that, in mice, a brain protein called Arc helps spread Tau from sick brain cells to healthy ones.

If therapies could be designed to target the spread, they could be a powerful tool to stop Alzheimer’s disease from getting worse.