Proper exercise can help--especially breathing. The brain needs oxygen to function properly.
There are also memory games and brain exercises which will help to keep the memory sharp or to improve memory. The brain is a muscle and has to be used in order for it to stay in shape. As we get older we have to workout more to keep our minds sharp, just as we have to work harder to keep our bodies functioning properly. The saying, "if you don't use it, you lose it" is very true when it comes to brain function. Doing puzzles, problem-solving, doing routines differently, learning something new, etc will help keep the brain active and alert.