Gambling Monkeys Reveal a Brain Area Responsible for High Risk Behavior

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A team of scientists from Johns Hopkins University taught monkeys how to gamble—and their experiments have revealed an area of the brain that plays an important role in risk-taking behavior.

The findings—which are published in the journal Current Biology—cast new light on the willingness of primates to take risks and could have important implications for the development of treatments for destructive, risky behaviors, such as gambling, in humans.

It is widely thought that one's willingness to take risks is a consistent trait in individuals, but research has shown that this isn't necessarily the case.

"A person can be risk-averse for some things but inclined to risk in others, like someone who saves a lot of money but also skydives," Veit Stuphorn, a co-author of the study from Johns Hopkins, said in a statement.

"The change in risk attitude happens in the prefrontal cortex and our findings for the first time identify one critically important area," he said.

The prefrontal cortex is a region at the front of the brain which is thought to be involved in planning complex cognitive behavior, the expression of personality, decision-making and moderating social behavior.

In their experiments, the team trained two rhesus monkeys over the course of several months to play a game in which they gambled against a computer to win a reward of water. They did this by indicating the amount of reward and the probability of of winning using specific visual cues.

"First, we trained the monkeys that a range of different colors indicated different amounts of water—for example, red equals one drop, blue equals two drops, etc.," Stuphorn told Newsweek. "The monkeys learned this very fast. When the monkeys had understood the color code, we presented them with reward options that contained two colors. These were the gambles, where two different outcomes were possible."

"The exact outcomes were indicated by the color combination—for example, a combination of red and blue would indicate either one or two drops of water," he said. "So, a visual cue that was filled half with red and half with blue would mean a 50 percent chance for either one or two drops. It took the monkeys much longer to learn the probability cue. That is likely, because it is harder to understand. The monkeys need to experience a particular gamble for a number of times to understand the different frequencies of outcomes."

All of the gamble visual cues were presented to the monkeys on a computer screen as two colorful squares on a grey background.

"Directly after presentation of the gamble cues, the monkeys could choose between them by looking at either a gamble cue or the other," Stuphorn said. "The unchosen gamble cue disappeared and they had to fixate on the chosen cue for a while before they were informed about the outcome. Then they received the water."

Interestingly, both primates appeared to be natural risk-takers, preferring gambles where the odds were against them but the reward was better, versus those where they had a much higher chance of winning but would get a smaller reward.

Specifically, when the monkeys were given a choice between a 20 percent chance to win 10 milliliters of water and a 80 percent chance to win three milliliters, they consistently, went for the riskier gamble, even if they weren't thirsty.

According to the researchers, this suggests that the monkeys simply liked the excitement of winning, because there was no rational reason to go for the bigger gamble when they didn't need to extra water.

However, the researchers found that when they temporarily deactivated a specific area in the prefrontal cortex of the monkeys, known as the "supplementary eye field" (SEF), the animals risk-taking behavior dramatically reduced. The precise function of the SEF, is not yet fully known.

"This was truly unexpected, to find a brain section so specifically tied to risk attitude," Stuphorn said. "The monkey's preference markedly changed from really liking risk to liking it much, much less."

Humans have very similar brain structures to monkeys, so the researchers think that these findings should also apply to us.

"We have just started to 'take apart' the circuits that control risky behavior," Stuphorn said. "By better understanding it, we might at some point be able to help people that have problems handling risk appropriately."

This article has been updated to include additional comments from Veit Stuphorn.