This new “plastic” understanding has major practical implications for how we treat brain problems and maintain brain health. And it has led to some surprising discoveries.

Consider dementia, which in some form affects some 15% of people in the U.S. over age 70 and advances rapidly as we age. A brain with Alzheimer’s, the most common form of dementia, turns out, by various measures, to be a brain that is losing its overall plasticity. It shrinks and loses connections. But a growing body of research has found that exercise, both mental and physical, can lower the risk of experiencing dementia.

Last year, Peter Elwood and a team from the Cochrane Institute of Primary Care and Public Health at Cardiff University in the U.K. released results from the most detailed study ever done on the effect of lifestyle and exercise on the risk of getting dementia. The researchers followed 2,235 men—almost all the male inhabitants of Caerphilly, Wales, with initial ages between 45 and 59 years old—for 30 years.

They found that men who consistently did a few things reduced their risk for cognitive decline and dementia by a staggering 60%. These activities included eating a healthy diet (at least three to four servings of fruits and vegetables a day); maintaining a normal weight, with a body-mass index of 18 and 25; limiting alcohol to about a glass of wine a day; and not smoking.