Jim Holt has a great article on the strange neural anatomy of mathematics in the new New Yorker:
One morning in September, 1989, a forme sales representative in his mid-fortie entered an examination room with Stanisla Dehaene, a young neuroscientist based in Paris Three years earlier, the man, whom researcher came to refer to as Mr. N, had sustained a brai hemorrhage that left him with an enormous lesion in the rear half of his lef hemisphere. He suffered from severe handicaps: his right arm was in a sling; h couldn’t read; and his speech was painfully slow. He had once been married, wit two daughters, but was now incapable of leading an independent life and live with his elderly parents. Dehaene had been invited to see him because hi impairments included severe acalculia, a general term for any one of severa deficits in number processing. When asked to add 2 and 2, he answered “three. He could still count and recite a sequence like 2, 4, 6, 8, but he was incapable o counting downward from 9, differentiating odd and even numbers, or recognizin the numeral 5 when it was flashed in front of him.
Read the whole thing. Math, like reading, is a fascinating example of an innate cognitive talent that has been utterly transformed by culture. We’ve taken this crude ability to count and turned it into calculus. The problem is that, even as the human species has learned to deal with increasingly complex kinds of numbers, we are trapped inside a brain that’s the messy product of evolution. The Pleistocene era didn’t have algebra. (As Gary Marcus puts it, we are kluge.) This means that even the most abstract of equations are intertwined with seemingly irrelevant psychological variables:
A few years ago, while analyzing an experiment on number comparisons, Dehaene noticed that subjects performed better with large numbers if they held the response key in their right hand but did better with small numbers if they held the response key in their left hand. Strangely, if the subjects were made to cross their hands, the effect was reversed. The actual hand used to make the response was, it seemed, irrelevant; it was space itself that the subjects unconsciously associated with larger or smaller numbers. Dehaene hypothesizes that the neural circuitry for number and the circuitry for location overlap. He even suspects that this may be why travellers get disoriented entering Terminal 2 of Paris’s Charles de Gaulle Airport, where small-numbered gates are on the right and large-numbered gates are on the left. “It’s become a whole industry now to see how we associate number to space and space to number,” Dehaene said. “And we’re finding the association goes very, very deep in the brain.”