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In Lab Turned Casino, Gambling Monkeys Help Scientists Find Risk-Taking Brain Area

The fix was in for this rhesus macaque drinking juice on the Ganges River in Rishikesh, Uttarakhand, India. No gambling was required to get the reward.
Getty Images/Westend61 RM
The fix was in for this rhesus macaque drinking juice on the Ganges River in Rishikesh, Uttarakhand, India. No gambling was required to get the reward.

Experiments with two gambling monkeys have revealed a small area in the brain that plays a big role in risky decisions.

When researchers inactivated this region in the prefrontal cortex, the rhesus monkeys became less inclined to choose a long shot over a sure thing, the team reported Thursday in the journal Current Biology.

"They did not like the gambles anymore," says Veit Stuphorn, an author of the study and an associate professor at Johns Hopkins University.

The finding in our fellow primates adds to the evidence that human brains are capable of constantly adjusting our willingness to take risks, depending on factors such as what's at stake.

"For a long time, people thought that this is like a personality trait, that some people are risk-takers and others are not," Stuphorn says. But recent research has shown that the same person who is very cautious about personal investments may be an avid bungee jumper.

This study involved two monkeys that learned to play a computer game that gave them drops of juice when they won. The monkeys played voluntarily because they liked to gamble, Stuphorn says.

The game offered two options. The first was a juice reward that was guaranteed, but usually small. The second was a gamble: It might bring a lot of juice, or none.

The monkeys moved their eyes to indicate their choice in each round.

"They're always tempted to go for it," Stuphorn says. "They're going for the big win every single time," even when safe bets would have won them more juice overall.

Stuphorn's team suspected that this preference for long shots was linked to activity in a small area of brain in the prefrontal cortex that's involved in eye movements. When a monkey won big, brain cells in this area got really active.

But that jump alone didn't prove that these cells were affecting the monkey's behavior. So the researchers did another experiment that temporarily inactivated the brain area by cooling it.

And once the area was inactivated, the gambling monkeys played it safe. The monkeys were more likely to choose the guaranteed juice option, Stuphorn says

The finding shows at least one way the brain can change an individual's willingness to take risks, says Alireza Soltani, who studies decision-making at Dartmouth College and wasn't involved in the study. And the change probably depends on a lot of factors, he says, including what's at stake.

"The monkeys are playing for a drop of juice and that's not a big deal," Soltani says. So they take big risks just to keep the game interesting.

Other studies have found that both monkeys and people are more likely to hedge their bets when the stakes are higher. And scientists think the brain circuitry is probably similar.

The idea that the brain is constantly adjusting our view of risk has big implications for society, Soltani says.

"If you look at risk preference as not something that is fixed and set in stone," he says, "then we can actually think about what we can do to help people to change their risk preference to something that is better for them."

The brain area identified in the monkey study is involved in eye movement. But it's unclear whether this same area affects risk preferences that involve other types of movement, says Michael Platt, James S. Riepe University Professor of neuroscience, marketing and psychology of the University of Pennsylvania.

He suspects that different brain areas with a similar function may influence other risky behaviors, "whether that's reaching out to pull the handle on a slot machine or walking to the casino in the first place."

Understanding the circuits that influence risk-taking could have some important practical applications, Platt says.

"One would be to help people who have decision-making disorders, whether that's problem gambling or addiction, or other things like that," he says. "So we might be able to develop more effective therapies."

Understanding why our brains sometimes tell us to do something risky also could help all of us make better decisions, Platt says.

Copyright 2020 NPR. To see more, visit https://www.npr.org.

Jon Hamilton is a correspondent for NPR's Science Desk. Currently he focuses on neuroscience and health risks.