Some time ago, I forgot where I parked my car. After walking aimlessly around the parking garage for a while, I realized I had carpooled to work that day. I felt silly, and attributed my mistake to habituation (unfortunately, I can't carpool very often).
However, if this same incident would have happened to an older person, they would likely become worried about their brain health. According to the New York Times, there is a growing "brain fitness" industry (link to story). There is commercial "neurosoftware" that trains your brain with memory and math problems, and there are monthly-fee websites that offer tailored brain exercises.
Today, as Eric and I were driving to meet the Sunday group run, we were listening to a radio interview on the matter (it is funny how sometimes you receive information about a topic in clusters). John Medina, a researcher at Seattle Pacific University, studies the brain. He wrote a book ("Brain Rules") describing 12 principles for "surviving and thriving at work, home, and school."
The first rule is "Exercise boosts brain power". His theory is that the brain evolved while humans were in almost constant motion (our ancestors probably walked 15-20 miles a day). Thanks to this research, there is a new trend of having a treadmill at the office, and walk while you work on your computer (see this story).
If you want to learn more about this interesting topic, visit http://www.brainrules.net/. You can find the rest of the rules there.
So, now you know, exercise is not only about improving your physical performance, moving helps you upstairs too.