PICTURE YOURSELF AT a Las Vegas poker table, holding a bad hand – one with a very low chance of winning. Even so, the sight of the large stack of chips that piled up during a recent lucky streak nudges you to place a large bet anyway.

Why do people make high-risk decisions – not just at casinos, but also in other aspects of their lives – even when they’re aware that the odds are stacked against them? 

A team at John Hopkins University has found that the decision to “up the ante”, even in the face of long odds, is the result of an internal bias that adds up over time and involves a “push-pull” dynamic between the brain’s two hemispheres. 

Whether you are suffering from a losing streak or riding a wave of wins, your cumulative feelings from each preceding hand all contribute to this nudge factor, the author said. 

The research has been published in the Proceedings of the National Academy of Sciences journal. 

“What we learned is that there is a bias that develops over time that may make people view risk differently,” senior author Sridevi Sarma said. 

Risk game 

Sarma’s group sought to understand why people tend to take risks even when the odds are against them or avoid risk even when the odds are favourable. They also sought to learn where in the human brain such behaviour originates. 

To do so, they asked patients at the Cleveland Clinic’s Epilepsy Monitoring Unit to play a simple card game involving risk-taking.

The patients had undergone stereoelectroencephalography, a procedure in which doctors implanted multiple deep-seated electrodes in their brains, that was designed to allow the doctors to locate the source of seizures for future surgical treatment. 

The electrodes also allowed Sarma and her team an intimate look at the patients’ brains in real time, as they made decisions while gambling against a computer in a card game.

The game was simple – the computer had an infinite deck of cards with only five different values – 2, 4, 6, 8 and 10 – each of which was equally likely to be dealt. Following every found, the cards went back into the deck, leaving odds unchanged. 

Participants were shown two cards on a computer screen, one face up (the player’s) and the other face down (the computer’s). Participants were asked to bet low ($5) or high ($20) that their card had a higher value than the computer’s facedown one.

When dealt a 2, 4, 8, or 10, participants bet quickly and instinctively, the research team found.

When dealt a 6, however, they wavered and were nudged into betting higher or lower depending on their bias – even though the chances of picking a higher or lower card were the same as before.

In other words, participants’ betting behaviour was based on how they fared on past bets even though those results had no bearing on the outcome of the new bets.

Taking the risk

After examining neural signals recorded during the game, Sarma’s team found a predominance of high-frequency gamma brain waves. 

They were able to localise these to particular structures in the brain. It turns out that these regions – excluding any implicated in drug-resistant epilepsy – were associated positively or negatively with risk-taking behaviour.

“When your right brain has high-frequency activity and you get a gamble, you’re pushed to take more of a risk,” Pierre Sacré, co-author of the study, said.

He expressed surprise at the symmetry of the patients’ brain reactions under these conditions. 

“But if the left side has high-frequency activity, it’s pulling you away from taking a risk. We call this a push-pull system.” 

To assess that internal bias, the researchers developed a mathematical equation that successfully calculated each patient’s bias using only their past wagers. 

“We found that if you actually solve for what this looks like over time, the players are accumulating all the past card values and all the past outcomes, but with a fading memory,” Sarma said. 

“In other words, what happened most recently weighs on a person more than older events do. This means that based on the history of a participant’s bets, we can predict how that person is feeling as they gamble.”