THURSDAY, Oct. 5, 2006 (HealthDay News) -- Civil society may hinge on a tiny piece of tissue at the front of the human brain, a new study suggests.
Experiments involving a "fairness" game show that the right side of this region -- called the dorsolateral prefrontal cortex -- helps people suppress selfish urges in obviously unjust situations, even at their own expense.
When researchers used a mild electric current to temporarily short-circuit this area, the law of the jungle quickly reasserted itself.
People with disabled right-side dorsolateral prefrontal cortexes grabbed whatever money they could from lopsided transactions -- even when they knew the deal they were getting was grossly unfair.
"They understood the unfairness of it all, but they simply couldn't inhibit their need for getting the money," said Paul Sanberg, director of the Center of Excellence for Aging and Brain Repair at the University of South Florida College of Medicine in Tampa.
Sanberg was not involved in the study, which is published in the Oct. 6 issue of Science.
The Swiss and American team behind this research noted that, despite a long history of crime, wars and rapaciousness, human beings are innately cooperative. In fact, Homo sapiens is the only species to exhibit "reciprocal fairness" -- the punishment of others' unfair behaviors, even in situations where doing so hurts the punisher.
This behavior is demonstrated in an oft-used tool in behavioral science called the "Ultimatum Game."
In this game, one player is given a set amount of money. He is then instructed to hand over, at his own discretion, a share of the money to a second player.
Player 2 can either accept the amount offered or refuse the deal altogether, in which case both players receive no money.
When Player 1's offer is very low -- for example, $2 out of a total of $20 -- it would still behoove Player 2 to accept the offer, since $2 is better than nothing.
However, under normal circumstances, participants put in this position in the game overwhelming refuse such low offers, which they perceive as grossly unfair. Instead, they forfeit their own self-interest so they can "punish" Player 1.
Why might this be so? Humans are highly socially evolved, and punishing unfairness "helps sustain cooperation in groups," said study lead researcher Ernst Fehr, director of the Institute for Empirical Research in Economics at the University of Zurich.
Because more cohesive groups tend to have better survival prospects, humans who suppress their immediate urges end up on the "winning team," evolutionarily speaking.
Fehr's group sought to find the seat of this selfishness-override in the brain.
In prior brain-imaging studies, the dorsolateral prefrontal cortex (DLPFC) lit up during the game, so the researchers focused there.
In the study, they had participants play the game under two conditions. In the first condition, the researchers passed a mild electric current through the right or left hemispheres of Player 2's DLPFC, temporarily deactivating these brain regions. Other participants took on the Player 2 role under sham conditions where no real electric current was flowing.
"The big surprise," Fehr said, "is that a relatively minor inhibition of the right DLPFC removes or weakens the subject's ability to override their self-interest."
Players whose right-side DLPFC's were "switched off" accepted even very low amounts of cash nearly half (45 percent) of the time -- even though they knew the offer was terribly unfair.
But under normal conditions, barely one in 10 players accepted such insulting low offers, the researchers found.
The experiment shows that this part of the cortex "is clearly very important for our social behavior, our societal evolution," Sanberg said. The right side of the DLPFC helps people resist those strong urges for sex, money and general acquisitiveness that come from more primitive sites outside the cortex, he said.
"It provides modulation of those urges, so that you can have control over them," Sanberg added. "As we evolved, we somehow developed this control over our basic needs."
One intriguing line of research is whether the right-side DLPFC functions similarly in everyone -- even hardened criminals or sociopaths.
"This is a very interesting question which we are just exploring now," Fehr said. "Preliminary results suggest that the right DLPFC has very different activation across individuals."
His team also noticed that the left side of the DLPFC also sprang to life during the game, although its role remains much more mysterious. "We are just in the process of studying this now," Fehr said.
More information
There's more on the brain and brain imaging at the U.S. National Institutes of Health.
