Stress may cause long-term cognitive deficiencies, too. Coe subjects pregnant monkeys to three loud car-horn bursts at unpredictable intervals over a 10-minute period, and he does it daily for one-quarter of their pregnancy. "Certainly women living in the Congo or in Iraq have a much more stressful pregnancy than anything I ever studied," he says. Yet even this moderate amount of stress results in infant monkeys that are less able to hold up their heads or scrutinize novel objects. At three years old, their hippocampus, a brain area responsible for learning and memory, is 10 percent smaller than normal, which likely translates into worse functioning.