Monkeys show regret when they lose at rock, scissors, paper...

We humans tend to think of ourselves as the only sentient beings capable of regret, a key emotion that helps keep us from making the same mistakes over and over. Now a new study shows that rhesus monkeys may be saddled with the same feelings of disappointment — at least when they lose at rock, paper, scissors.

A duo of researchers from Yale School of Medicine taught the animals to play a modified version of the popular childhood game. When the monkey won, it got a large container of juice as a reward. If the monkey and the researcher tied, the monkey was given a smaller reward. Monkeys that lost were given nothing. These monkeys displayed regret about their missteps, said Daeyeol Lee, a professor of neurobiology at Yale School of Medicine and the Kavli Institute for Neuroscience, and Hiroshi Abe of Yale medical school's department of neurobiology.

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How do they know? Because each time a monkey lost, it was more likely in the next round to use the gesture that would have won in the previous one (so, for instance, if the researcher's rock beat the monkey's scissors, the monkey was more likely to throw a rock in the next round). That suggests the monkeys were capable of analyzing past results and imagining a different outcome, the researchers said.

In a second experiment, Lee and Abe recorded the monkeys' neuronal function as they played the game, hoping to get a better understanding of how regret registers in the brain. When the monkeys lost, they showed activity in two regions of the brain associated with the rational and emotional components of regret: the dorsolateral prefrontal cortex, which is involved in working memory, and the orbitofrontal cortex, which is associated with the emotional aspect of regret.

Lee and Abe hope their findings can be used to help treat patients who suffer from pathological regret, such as mental illnesses that lead patients to obsess over past decisions that led to poor outcomes. "Regret serves us well most of the time, by helping us recognize choices that lead to bad outcomes," said Lee in a statement. "But sometimes regret can be very damaging."

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