A decade ago, a neuroscientist named Charles Nelson traveled to Bucharest to visit Romania’s infamous orphanages. There, he saw a child whose brain had swelled to the size of a basketball because of an untreated infection and a malnourished one-year-old no bigger than a newborn. But what has stayed with him ever since was the eerie quiet of the infant wards. “It would be dead silent, all of [the babies] sitting on their backs and staring at the ceiling,” says Nelson, who is now at Harvard. “Why cry when nobody is going to pay attention to you?”

Nelson had traveled to Romania to take part in a cutting-edge experiment. It was ten years after the fall of the Communist dictator Nicolae Ceauşescu, whose scheme for increasing the country’s population through bans on birth control and abortion had filled state-run institutions with children their parents couldn’t support. Images from the orphanages had prompted an outpouring of international aid and a rush from parents around the world to adopt the children. But ten years later, the new government remained convinced that the institutions were a good idea—and was still warehousing at least 60,000 kids, some of them born after the old regime’s fall, in facilities where many received almost no meaningful human interaction. With backing from the MacArthur Foundation, and help from a sympathetic Romanian official, Nelson and colleagues from Harvard, Tulane, and the University of Maryland prevailed upon the government to allow them to remove some of the children from the orphanages and place them with foster families. Then, the researchers would observe how they fared over time in comparison with the children still in the orphanages. They would also track a third set of children, who were with their original parents, as a control group.

In the field of child development, this study—now known as the Bucharest Early Intervention Project—was nearly unprecedented. Most such research is performed on animals, because it would be unethical to expose human subjects to neglect or abuse. But here the investigators were taking a group of children out of danger. The orphanages, moreover, provided a sufficiently large sample of kids, all from the same place and all raised in the same miserable conditions. The only variable would be the removal from the institutions, allowing researchers to isolate the effects of neglect on the brain.

Prior to the project, investigators had observed that the orphans had a high frequency of serious developmental problems, from diminished IQs to extreme difficulty forming emotional attachments. Meanwhile, imaging and other tests revealed that some of the orphans had reduced activity in their brains. The Bucharest project confirmed that these findings were more than random observations. It also uncovered a striking pattern: Orphans who went to foster homes before their second birthdays often recovered some of their abilities. Those who went to foster homes after that point rarely did.