From the article:
Good mental and physical exercises are thought to help with brain functioning as we age. But the devil is in the details and inside the brain itself, which has a mind of its own—in a manner of speaking—that is difficult to read. Researchers have many theories about how our brains change as we grow older. Their discoveries have overturned some old assumptions, but scientists necessarily are cautious about applying to humans the findings from experiments done on animals. The brain still is largely a frontier.