New insights into how the brain processes social, economic reward

Apr 23 2008

Researchers have mapped the brain regions that process social standing and money rewards, yielding new insights that they said will aid understanding of the basis of social behaviors.

They published their findings in two papers in the April 24, 2008, issue of the journal Neuron, published by Cell Press.

In one paper, Norihiro Sadato and colleagues found that making money and making a reputation engage much of the same reward circuitry in the brain-a finding that they say yields insight into what drives complex social behaviors.

In the other paper, Caroline Zink and colleagues mapped brain regions that are active when a person is processing information on social status. The researchers said their findings could yield insight into why social status can so profoundly affect behavior and health.

Also, the papers' findings could offer an understanding of why drug treatments for such neurological disorders as Parkinson's disease can trigger abnormal money-related behaviors such as compulsive gambling, commented Rebecca Saxe and Johannes Haushofer in a preview of the two papers in the same issue of Neuron.

In the first paper, Sadato and colleagues compared the activation of specific areas of volunteers' brains as they took part in two experiments in which they received either money or social rewards. During the experiments, the researchers scanned the subjects' brains using functional magnetic resonance imaging (fMRI), in which harmless magnetic fields and radio waves are used to measure blood flow in brain regions, which reflects activity.

In the monetary reward experiments, the subjects were told they were playing a gambling game, in which they chose one of three cards to receive a payoff. However, the researchers manipulated the game so that they could determine the brain activity triggered by high rewards.

In the social reward experiment, the subjects were told that strangers would be evaluating them based on information from a personality questionnaire and a video they made introducing themselves. The subjects were shown a picture of themselves, along with the word or phrase indicating how the strangers had evaluated them. However, the strangers did not really exist, and the researchers showed the subjects predetermined evaluations that allowed the researchers to manipulate the level of social reward experienced by the subjects.

Sadato and colleagues found that both the monetary and social rewards activated a reward-related area of the brain called the striatum.

"By directly contrasting the brain activities of the same subjects in relation to the delivery of social and monetary rewards, our results clearly show that social approval shares the same neural basis as monetary rewards, thus providing strong support for the idea of a 'common neural currency' of reward," concluded the researchers.

They wrote that their findings "indicate that the social reward of a good reputation should be incorporated into the neural model of human decision making in a similar manner to monetary rewards." Thus, they wrote, experiments on decision making that use money-related games need to take into account that the subjects are exchanging more than money; they are also dealing in approval and reputation.

"Our findings indicate that the social reward of a good reputation in the eyes of others is processed in an anatomically and functionally similar manner to monetary rewards, and these results represent an essential step toward a complete neural understanding of human social behaviors," concluded Sadato and colleagues.

In the second Neuron paper, Zink and colleagues explored the neural regions activated when people process information on their social status. Such insights, they said, are significant because social hierarchies are important factors in social behavior, and "in humans, social status strongly predicts well-being, morbidity, and even survival."

In their experiments, the researchers set up artificial social hierarchies by asking volunteers to play simple interactive games for a money reward. Each of the volunteers was told that they were playing the games along with two other players, one of whom was a superior player and one an inferior player. However, in reality, the other players did not exist, and the game outcomes were manipulated so that the researchers could control the social status of the player. To give the illusion that the other players existed, the subjects saw the other players' images on the screen during play. Importantly, the games were noncompetitive, so that the researchers could measure only social status and its change.

During the games, the subjects' brains were scanned using fMRI, so the researchers could map the brain regions active during different conditions of social hierarchy.

In the first experiment, the researchers kept the social hierarchy stable. The subjects were asked to respond as quickly as possible when a blue circle on a computer screen changed to green. Throughout the game, the players' status did not change relative to the other "players."

In the second experiment, the researchers made the social hierarchy unstable, manipulating the outcome so that the player might do better or worse than the other "players." In that game, the player was asked to respond as quickly as possible to indicate which of two boxes on the computer screen contained the most black dots. Periodically during the game, the player would be told whether his/her status was rising or falling compared to the other "players."

In the third experiment, the researchers told the players they were playing against a computer, allowing the researchers to pinpoint the brain regions specifically activated by social behavior.

The researchers found they could distinguish brain regions that were more active when the subjects thought they were viewing a superior person compared with an inferior person, implicating these brain regions in the neural encoding of hierarchical rank.

Also, the researchers could distinguish brain areas that were particularly active when social hierarchy was changing. These areas included those involved in social emotional processing and social cognition.

"We conclude that activity in these regions represents an emotional arousal response to the superior player that only arises when the hierarchy is dynamic, i.e., when relative performance, although irrelevant for the game outcome, can have social hierarchical consequences," wrote the researchers.

Zink and colleagues wrote that "our findings demonstrate that brain responses to superiority and inferiority are dissociable, even in the absence of explicit competition, both when encountering an individual of a particular status and when faced with an outcome that can affect one's current position in the hierarchy. We hope that this research leads to identification of neural mechanisms mediating the enormous impact of social status on decision-making, health, and survival in humans."

"One immediate implication of these results is for patients with dysfunction of these brain regions," wrote Saxe and Haushofer in their preview. "The striatum is among the targets of some neurological disorders, such as Parkinson's disease (PD). Overtreatment of PD with dopamine agonists is known to induce abnormal economic decision-making, including compulsive gambling. If the same brain structures are responsible for the reward-value of love and reputation, pharmacological manipulation of the striatum may also have social consequences."