Like most rhesus monkeys, Aragorn is small and smart. Unlike most of his peers, however, Aragorn is also a practiced gambler.

He’s one of several rhesus monkeys – all named after “Lord of the Rings” characters – that Johns Hopkins University neuroscientist Veit Stuphorn has trained to perform what is formally known as “decision-making under risk.” The goal has been to look at how those choices unfold in the brain. And Stuphorn says his lab’s gambling monkeys have led to the discovery that an area of the brain is associated with high-risk tendencies – a finding that eventually could help scientists better understand such behavior in humans.

Stuphorn began working with monkeys about a decade ago, and Aragorn was the first. While the research doesn’t involve poker or blackjack, it has nonetheless been illustrative.

Veit starts by teaching the monkey to understand both color schemes and probability. Then the monkey is put in front of a computer screen and presented with two square boxes: one on the left and another of equal size on the right. Inside each box are colors – red, blue, green or a green-blue called cyan – that correspond to increasing rewards. In this case, the monkey plays for drinks of water.

The proportion of the colors in the box indicates the probability of a particular payoff. For instance, an all-blue box guarantees a medium amount of water. A box that’s 80 percent cyan and 20 percent green indicates a high chance of getting small amounts of water but a low chance of getting a lot of water. With each round, the monkey must decide between two options.

“The monkey used his eyes to make the choice,” said Stuphorn, explaining that researchers use sensors to track the animal’s eye movements. Whichever box its gaze fixes on indicates the animal’s choice, and the monkey then receives the associated reward – more water if the gamble pays off, less if it doesn’t. The trials last until the monkey has gotten its fill of water or gotten bored, which it sometimes makes very clear, Stuphorn said.

“They close their eyes and snore,” he said.


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