A team of neurobiologists at Duke University Medical Center believes it has identified the circuitry in the brains of rhesus macaque monkeys that assesses level of risk in a given action. Published in the online version of Nature Neuroscience, their findings may provide insights into why humans compulsively engage in risky behaviors such as gambling, unsafe sex, drug use and overeating.
In their experiments, researchers gave monkeys the chance to look at either of two target lights on a screen. One of the targets offered the same amount of juice every time, while the other target randomly yielded either a larger or smaller juice reward. The monkeys overwhelmingly preferred to gamble by looking at the risky target, even after researchers made the average payoff for the risky target less than that for the safe target.
"If they got a big reward one time on the risky choice, but then continued to get small rewards," researcher Michael Platt explained, "they would keep going back as if they were searching or waiting or hoping to get that big payoff. It seemed very, very similar to the experience of people who are compulsive gamblers.
"While it's always dangerous to anthropomorphize, it seemed as if these monkeys got a high out of getting a big reward that obliterated any memory of all the losses that they would experience following that big reward."
The researchers located the region of the brain excited by the risk decision by threading microelectrodes into the monkeys' posterior cingulated cortex.