Use it lose it!

"Research on the physical results of thinking has shown that just using the brain actually increases the number of dendritic branches that interconnect brain cells. The more we think, the better our brains function – regardless of age. The renowned brain researcher Dr. Marian Diamond says, "The nervous system possesses not just a 'morning' of plasticity, but an 'afternoon' and an 'evening' as well."

In fact, older brains may have an advantage. She discovered that more highly developed neurons respond even better to intellectual enrichment than less developed ones do. The greatest increase in dendritic length occurred in the outermost dendritic branches, as a reaction to new information.

As she poetically describes it: "We began with a nerve cell, which starts in the embryo as just a sort of sphere. It sends its first branch out to overcome ignorance. As it reaches out, it is gathering knowledge and it is becoming creative. Then we become a little more idealistic, generous, and altruistic; but it is our six-sided dendrites which give us wisdom."

http://www.fi.edu/learn/brain/exercise.html#top