Like a draft of wind, the smell of lunch moves across the mess hall at the Senior Life Center in Gainesville on a recent afternoon, tickling the nostrils of dozens of hungry visitors. So, when someone yells “Bingo!” it feels like an act of mercy to end the game and begin the feast. This moment, however, captures what medical researchers have come to learn about how a good diet, regular exercise and an active brain can stave off the onset of dementia. And this lesson is not lost on the Senior Center patrons, some of whom worry about the prospect of cognitive decline as they age.