“Until just a few years ago we doctors believed that the brain stopped making new neural connections ? meaning that your memory began to get irreversibly worse ? when the body stopped developing usually in your early 20s. And we knew that like any other body part neurons weaken as we age. Loss of brain function due to neural breakdown was assumed to be a normal unavoidable part of aging.

It turns out we were wrong. In the past few years it has become clear that you can in fact make new neurons starting in your 20s and continuing well into old age. You can literally rewire the brain with new parts as the older parts wear out. How? Simple: Keep learning. Just as your body can pack on and condition new muscle your brain can rebuild used-up neurons.

How strong is the evidence for this? Strong enough that a $200 million industry devoted to brain-boosting software ? products like Brain Age MindFit and Lumosity that supposedly improve your memory function ? has sprung up out of nowhere. The jury is still out on whether these programs actually sharpen the noggin as much as they claim to. But frankly you don’t need a fancy video game. All “mental fitness” means is keeping your memory intact ? everything from phone numbers to how to throw a football. 

Mehmet Oz is a heart surgeon and the coauthor of You: Staying Young (Free Press $26).