It's been shown that intellectually stimulating activities are good for the gray matter. It may also be good for the white matter.
Researchers at Rush University Medical Center and Illinois Institute of Technology in Chicago found that reading, writing or playing games such as chess and checkers may help keep the area of the brain known as white matter healthy. White matter transmits information throughout the central nervous system and the brain. Keeping white matter healthier helps preserve the structural integrity of the entire brain, researchers said. In their study of 152 participants with an average age of 81 and without signs of dementia, those who participated in what researchers called "more frequent cognitive activity in late life" displayed healthier brain patterns.