Want to have the brain of a 25-year-old when you reach your 70th birthday? All you have to do is exercise your grey matter. Here are the details:

Researchers at the University of California gave healthy senior citizens PET scans to measure the buildup of certain proteins in their brains, which have been linked to cognitive diseases like dementia and Alzheimer’s. They measured the same chemicals in groups of college students and Alzheimer’s patients. They also asked participants about their work and hobbies in order to see how often they engaged in intellectually-challenging activities.

The result: The seniors who regularly pursued activities, like learning a language, taking up an instrument, or solving puzzles, had lower levels of brain-harming proteins. In fact, those who were the most mentally active had levels similar to the 25-year-olds. Those who didn’t challenge themselves had chemical levels closer to those of the Alzheimer's patients.

The study’s lead author, Dr. William Jagust, says it’s not yet clear why stimulating your mind reduces the risk of Alzheimer’s. He suspects that mental exercise makes your brain more efficient at removing the damaging proteins, and if it helps, we should all keep our brains more active.