The waltz won’t do. Nor will the rumba. Looks like the good old-fashioned square dance, AKA contra dancing, accompanied by a fiddle and a helpful caller, could keep older brains firing on all pistons. At least that’s the conclusion of a Colorado State University study that tracked what happens to “white matter” in the brains of older adults. The CSU research team found that dance training in contra or English country dancing — think square dancing, but in lines — seems to have a positive effect on the fornix, a white-matter tract in the middle of the brain that is basically the brain’s wiring.