as always been a form of exile, of being cut off from the larger society. But the distance between the poor and the rest of us is much greater than it was 40 years ago, because most American incomes have risen in real terms while the official poverty line has not. To be poor in America today, even more than in the past, is to be an outcast in your own country. And that, the neuroscientists tell us, is what poisons a child’s brain.