3 Your plane has been taken over by a terrorist. He has taken a passenger’s baby hostage and is holding a knife to his throat. Do you rush the terrorist to subdue him, knowing that the baby will die before you get there? |
When neuroscientists first started scanning brains in the early 1990s, they studied the basic building blocks of thought, such as language, vision, and attention. But in recent years, they’ve also tried to understand how the brain works when people interact. Humans turn out to have special neural networks that give them what many cognitive neuroscientists call social intelligence. Some regions can respond to smiles, frowns, and other expressions in a tenth of a second. Others help us get inside a person’s head and figure out intentions. When neuroscientist Jonathan Cohen came to Princeton to head the center, he hoped he could dedicate some time with the scanner to study the interaction between cognition and emotion. Greene’s morality study was a perfect fit.
Working with Cohen and other scientists at the center, Greene decided to compare how the brain responds to different questions. He took the trolley problem as his starting point, then invented questions designed to place volunteers on a spectrum of moral judgment. Some questions involved personal moral choices; some were impersonal but no less moral. Others were utterly innocuous, such as deciding whether to take a train or a bus to work. Greene could then peel away the brain’s general decision-making circuits and focus in on the neural patterns that differentiate personal from impersonal thought.
Some scenarios were awful, but Greene suspected people would make quick decisions about them. Should you kill a friend’s sick father so he can collect on the insurance policy? Of course not. But other questions—like the one about the smothered baby—were as agonizing as they were gruesome. Greene calls these doozies. “If they weren’t creepy, we wouldn’t be doing our job,” he says.
As Greene’s subjects mulled over his questions, the scanner measured the activity in their brains. When all the questions had flashed before the volunteers, Greene was left with gigabytes of data, which then had to be mapped onto a picture of the brain. “It’s not hard, like philosophy hard, but there are so many details to keep track of,” he says. When he was done, he experienced a “pitter-patter heartbeat moment.” Just as he had predicted, personal moral decisions tended to stimulate certain parts of the brain more than impersonal moral decisions.
The more people Greene scanned, the clearer the pattern became: Impersonal moral decisions (like whether to throw a switch on a trolley) triggered many of the same parts of the brain as nonmoral questions do (such as whether you should take the train or the bus to work). Among the regions that became active was a patch on the surface of the brain near the temples. This region, known as the dorsolateral prefrontal cortex, is vital for logical thinking. Neuroscientists believe it helps keep track of several pieces of information at once so that they can be compared. “We’re using our brains to make decisions about things that evolution hasn’t wired us up for,” Greene says.
Personal moral questions lit up other areas. One, located in the cleft of the brain behind the center of the forehead, plays a crucial role in understanding what other people are thinking or feeling. A second, known as the superior temporal sulcus, is located just above the ear; it gathers information about people from the way they move their lips, eyes, and hands. A third, made up of parts of two adjacent regions known as the posterior cingulate and the precuneus, becomes active when people feel strong emotions.
Greene suspects these regions are part of a neural network that produces the emotional instincts behind many of our moral judgments. The superior temporal sulcus may help make us aware of others who would be harmed. Mind reading lets us appreciate their suffering. The precuneus may help trigger a negative feeling—an inarticulate sense, for example, that killing someone is plain wrong.
When Greene and his coworkers first began their study, not a single scan of the brain’s moral decision-making process had been published. Now a number of other scientists are investigating the neural basis of morality, and their results are converging on some of the same ideas. “The neuroanatomy seems to be coming together,” Greene says.
Another team of neuroscientists at Princeton, for instance, has pinpointed neural circuits that govern the sense of fairness. Economists have known for a long time that humans, like capuchin monkeys, get annoyed to an irrational degree when they feel they’re getting shortchanged. A classic example of this phenomenon crops up during the “ultimatum game,” in which two players are given a chance to split some money. One player proposes the split, and the other can accept or reject it—but if he rejects it, neither player gets anything.
If both players act in a purely rational way, as most economists assume people act, the game should have a predictable result. The first player will offer the second the worst possible split, and the second will be obliged to accept it. A little money, after all, is better than none. But in experiment after experiment, players tend to offer something close to a 50-50 split. Even more remarkably, when they offer significantly less than half, they’re often rejected.
The Princeton team (led by Alan Sanfey, now at the University of Arizona) sought to explain that rejection by having people play the ultimatum game while in the MRI scanner. Their subjects always played the part of the responder. In some cases the proposer was another person; in others it was a computer. Sanfey found that unfair offers from human players—more than those from the computer—triggered pronounced reactions in a strip of the brain called the anterior insula. Previous studies had shown that this area produces feelings of anger and disgust. The stronger the response, Sanfey and his colleagues found, the more likely the subject would reject the offer.
