If you want your brain to stay sharp, you have to work it. "I write complex code every day of the week. That's all the brain exercise I need." you say. But you're wrong. If you want to keep your brain alive, you have to do things your brain doesn't expect. The cortex forms new patterns... new synaptic connections in response to novel activity, and PET scans show that far fewer pathways are activated when the brain processes a routine task... even a complex one.
The point is to do something different.
Turn your world upside down
"Turn pictures of your family, your deskclock, or an illustrated calendar upside down. Your brain is quite literally of two minds when it comes to processing visual information. The analytical "verbal" part of your brain (sometimes called "the left brain") tries to label on object after just a brief glance: "table", "chair", "child". The "right brain", in contrast, perceives spatial realtionships and uses nonverbal cues. When you look at a familiar picture right side up, your left brain quickly labels it an diverts your attention to other things. When the picture is upside down, the quick labeling strategy doesn't work--and your right-brain networks kick in, trying to interpret the shapes, colors, and relationships of a puzzling picture."
See things in a new light
"Place different-color geletain filters over your desk lamp. Colors evoke strong emotional associations that can create completely different feelings about ordinary objects and events. In addition, the occasionally odd effects of color (a purple styrofoam coffee cup) jars your brain's expectations and lights up more blips on your attentional "radar screen."
So what are you doing to blow your own mind on a regular basis?