Here is one of mental exercises featured by everydayhealth.com that can keep your brain sharp:
The morning newspaper is a great place to start.
“Simple games like Sudoku and word games are good, as well as comic strips where you find things that are different from one picture to the next,” said John E. Morley, MD, director of St. Louis University’s Division of Geriatric Medicine and author of The Science of Staying Young.
In addition to word games, Dr. Morley recommends the following exercises to sharpen your mental skills:
Test your recall. Make a list — of grocery items, things to do, or anything else that comes to mind — and memorize it. An hour or so later, see how many items you can recall. Make items on the list as challenging as possible for the greatest mental stimulation.
Draw a map from memory. After returning home from visiting a new place, try to draw a map of the area; repeat this exercise each time you visit a new location.
Do math in your head. Figure out problems without the aid of pencil, paper, or computer; you can make this more difficult by walking at the same time.