Take a careful look at the image of two brains on this page. The picture is of the brains of two three-year-old children. It’s obvious that the brain on the left is much bigger than the one on the right. The image on the left also has fewer spots, and far fewer dark “fuzzy” areas. To neurologists who study the brain, and who have worked out how to interpret the images, the difference between these two brains is both remarkable and shocking...