A study reported in Science Daily (read it here) out of the University of Arizona demonstrates by MRI increased connections between neural areas in endurance runners (cross country runners) compared to non-runners.

My question is whether the people with more connections somehow select running preferentially.  The only way to know is to do a cross over study and get some of the couch potatoes out running and convince some of the runners to stop for a year (not likely) and then re-image their brains.