Some people walk into a casino and head to the nickel slots; others march straight to the roulette table with their life savings.

Why? What makes us more prone to take risks?

The answer, according to research out Wednesday from Stanford University, is the failure of specific nerve cells in the brain to send out a signal that inhibits gambling behavior.

The discovery was made in an experiment aimed at studying brain chemistry in rats as they made decisions about whether to get a steady, regular reward or a rare, much larger reward.

“Humans and rats have similar brain structures involved,” says senior author and practicing psychiatrist Karl Deisseroth. “So every indication is that these findings are relevant to humans.”

High-Rolling Rodents

Researchers reached their conclusions after devising a task where rats poke their nose in a hole, at which point two levers pop out. When the rats pulled one lever, they received a dependable dose of sugar water. Pulling the other lever most of the time yielded a much smaller amount of sugar water, but a big rush of sugar water every once in a while.

Once they had learned the system, about two-thirds of the rats consistently chose the steady-paying dose. The other third preferred the occasional windfall. Like some people, a high-rolling rat doesn’t seem to be fazed by a losing streak.

The Brain and Risk

Heading into the study, researchers were fairly certain that a specific region of the brain called the nucleus accumbens was implicated in gambling behavior.

To test this, they gave the rats a drug called pramipexole; it’s prescribed for Parkinson’s disease, restless leg syndrome and other brain or nervous system disorders, and it can cause gambling problems.

The drug turned rats that chose the steady lever into rats looking for a big reward.

“We found that a drug known to increase risk preference in people had the same effect on the rats,” Deisseroth says.

Zeroing in on nucleus accumbens, scientists then discovered that a small group of nerve cells in the region lit up in the risk-averse rats, but not in those who were risk-prone.

That meant a rat was really bummed out after getting the smaller dose, and was more likely to choose the steadier payout the next time. But the risk taking rodents didn’t seem to care if they were disappointed most of the time as long as a big sugar rush arrived occasionally. In other words, the risk-prone rats were less sensitive to loss signals — they care less when they lose so they’re more likely to keep going for the win.

“It looks as though we have found a brain signal that, in most individuals, corresponds to a memory of a failed risky choice,” Deisseroth says. “It seems to represent the memory of that recent unfavorable outcome, manifested later at just the right time when it can — and does — modify an upcoming decision.”

Through a couple of different techniques, the researchers then manipulated the rats’ brains and found they could influence their choices, turning risk avoiders into risk seekers.

Could the Same Be True for People?

The researchers say the findings could inform human therapy down the road.

Brian Knutson, a professor of psychology at Stanford and a study co-author, says the research offers insight into both pharmacotherapy or even environmental cues that influence gambling addicts.

“Having this knowledge,” says Knutson, “knowing which chemicals, which receptors in the brain are responsible means that we can make better predictions about which drugs would increase risk-taking and which won’t.”

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