Check out this fascinating story by Benedict Carey that explores the reasons why certain older people (90 and over) are able to maintain their mental sharpness. In a nutshell: researchers have found little evidence that diet or exercise makes a difference (kind of surprising). So who makes it into the club? People who spend their days “engrossed in mental activities” like playing cards, trying new things, and maintaining rich social connections.  

Beyond giving insight into why my Grandma Kuhl and all her friends stayed so sharp well into their nineties (with pinochle, not bridge), this also makes abundant sense: Fire the circuit, and you earn more myelin.