updated 7/5/2012 2:19:49 PM ET 2012-07-05T18:19:49

Interacting with a person really is different from interacting with a computer — and the brain knows it.

Researchers have discovered that a region of the brain known to be important for understanding others' minds only gets active when people have to make decisions about social situations, but not when they have to make similar decisions without other human involvement.

"Basically, it's triggering the brain to play by different rules," said study researcher Scott Huettel, a neuroscientist at Duke University.

Making decisions

A long line of economics and psychology studies have found that humans tend to make different decisions when they're interacting with people than when they're interacting with a computer, Huettel told LiveScience. People are usually very good at weighing social information in decision-making: They focus on key players when making group decisions, they can tell the different between someone employing a strategy and someone acting randomly, and when they need to compare themselves to others, they tend to draw conclusions based on similar people.

Huettel and his colleagues wanted to understand how the brain differs when it has to make decisions in a social context versus a non-social one. To find out, they arranged for 18 volunteers to play a series of simplified poker games with both computers and a human opponent.

In both cases, the decision to make was the same. Participants were given either a high or low card and had to decide whether to bet against their opponent. If their card beat out their opponent's, or if they bluffed with a low card so that their opponent folded, the participant won money. Otherwise, the opponent got paid.

Before the experiments, the participants met their opponent and shook hands, making the situation as obviously social as possible, Huettel said. They were also told which games would be against a person and which were against a computer. The games then took place as participants rested inside a functional magnetic resonance imaging machine (fMRI). The fMRI measured blood flow to various brain regions in real time. An increase in blood flow to a specific region is a sign that region is becoming more active. [ Images: Peering Inside the Brain ]

The social brain

The resulting brain images revealed that one particular region got flooded with blood only during play versus another human and never during a game against a computer. This region, the temporoparietal junction, sits at the side of the head, right about where the brain's temporal and parietal lobes meet. The researchers report their findings in this week's issue of the journal Science.

"That region was the only one that carried unique information in social context," Huettel said. "It was carrying information that would let us better predict what [move] the human would chose in the human case, but it wouldn't predict it when they were playing against the computer."

There were differences in individual players' brains, however. After the experiment, the researchers asked the players if they thought the computer or the person was the superior opponent. The people who thought the person was better were the only ones who showed temporoparietal activity when playing against that person.

That suggests that the region depends on social context, probably only becoming active when the other person in the situation seems relevant and important, Huettel said. Previous research has found that the temporoparietal junction lights up with activity when people look at photographs of others like them, but not when they look at pictures of people who seem distant, such as photos of homeless people.  

The researchers are now conducting follow-up experiments that will pit experts against non-experts to see if these stratifications produce any different brain responses. They expect that the more expert a person is at the game, the less the temporoparietal region will activate in response to non-experts.

"The non-expert might be seen as someone not worth paying attention to," Huettel said.


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